Will Keysight upgrade the 2000, 3000T X-Series Oscilloscopes within a few months

[eeguy]

It looks like these InfiniVision scopes have been around for a few years. Heard anything about possible upgrade in the near future?

[Pinkus]

The moment they will tell you this, their sales will drop as people will wait purchasing a scope.
So...... you will not get such an information before the new product is ready to hit the market.
However, as the T series is quite new, I doubt we will see a new 2000/3000 series pendant from Keysight in the next 12-18 months.

[Faith]

As I like to say; "new equipment doesn't suddenly make old equipment useless."

There are many excellent oscilloscopes on the market already be it from Keysight or otherwise so there isn't really much of a point in worrying about whether or not something is going to be superseded because it's inevitable that whatever you buy from whomever will already have a replacement design in the works.

Ultimately there's a lot more to lose (in terms of time and productivity) not having the tools you need versus potentially missing out on whatever the "latest and greatest" has to offer.

[nctnico]

If you wait there will always be something better. IMHO the short memories on the 2000 and 3000 series makes them kind of obsolete. Keysight focussed way too much on insane waveform/s rates rather than adding something which is actually useful: more memory. If you can spend a couple of $k then I'd look at Lecroy's Wavesurfer 3000 series.

[JPortici]

though they did offer the MSO variant at the same price of the DSO for quite some time. that might indicate something (clearing out?)

[Wuerstchenhund]

It looks like these InfiniVision scopes have been around for a few years. Heard anything about possible upgrade in the near future?

unlikely, if anything we might see some slight refresh without any major changes (i.e. sample memory will remain the same).

DSOX2k, DSOX3k and DSOX4k (and their MSO variants) still sell very well. The DSOX6004 doesn't, though (but that shouldn't really surprise anyone considering in what scope class Keysight tries to compete with essentially a blown-up entry-level scope). Many corporate customers tend to buy single-source, so they get all test gear from Keysight (and no other manufacturer has a similarly wide ranged portfolio), and that includes scopes even though they might not offer the best bang for the buck. Also, corporate customers pay nowhere near RRP for their kit.

Also, don't forget that the DSOX3000T only came out in 2014, where it replaced the DSOX3000A. Giving the DSOX2kA the same update would very likely make it too expensive, and the DSOX4kA already has what the DSOX3kT got (the DSOX3kT is pretty much a DSOX4kA with smaller screen). There isn't a lot room for further updates.


It's true that from a technical point of view they are getting a bit long in the tooth (the tiny sample memory is a problem), and the excessive high waveform rates haven't shown to be such a massive advantage as Agilent/Keysight claimed in their marketing blah. But the limitations are mostly due to Keysight's architecture and with that there's always a trade-off between memory size and update rate, which they already decreased from 8M to 4M when moving from the DSO6k/7k to the DSOX to get these superhigh update rates. That means all they could do is going back to where the old DSO6k/7k scopes were. Not a lot to justify investing in setting up a new product.

And as long as the InfiniVision scopes sell well there's no need for Keysight to invest in a successor. And as someone else said, even if they had plans then they're not going to make them public before launch date to protect their existing sales.

As someone already said, there are lots of scopes out there. If the DSOX isn't what you want then buy something else. And if you insist on Keysight then you'll probbaly have to live with what they're offering. That's how it works.

BTW: the DSOX (which I think came out in 2011) isn't really *that* old. Just look at Tek, who sells pretty much the same outdated scope design in slight variations for more than a decade.

[Wuerstchenhund]

though they did offer the MSO variant at the same price of the DSO for quite some time. that might indicate something (clearing out?)

No, that's just one of their regular promos that come and go.

[JPortici]

though they did offer the MSO variant at the same price of the DSO for quite some time. that might indicate something (clearing out?)

No, that's just one of their regular promos that come and go.

i see. while i still was a student i used to work in (electronics) retail and you should know, for consumer level stuff every sale is just to empty the stock usually, the more the discount the more you should stay away from it

[Wuerstchenhund]

though they did offer the MSO variant at the same price of the DSO for quite some time. that might indicate something (clearing out?)

No, that's just one of their regular promos that come and go.

i see. while i still was a student i used to work in (electronics) retail and you should know, for consumer level stuff every sale is just to empty the stock usually, the more the discount the more you should stay away from it

It's somewhat different for test gear. Manufacturers come up with promos when they believe they need to push their product a little, or when a competitor comes out with a promo which they want to match. Promos are rarely related to product changes.

Promos aren't good value in my opinion because they usually prohibit the use of any other form of discounts, and you can usually get the same options included at a better price when trying to haggle.

Also, just because a new model of scope came out doesn't mean the predecessor gets sold at huge discounts (just look at DSO6k/7k prices when the DSOX came out). Usually the old model is kept in the portfolio for a while to keep certain customers happy, until it's sold out.

[eeguy]

though they did offer the MSO variant at the same price of the DSO for quite some time. that might indicate something (clearing out?)

Yes it is still on until next year. Have they ever offered promotions such as more bandwidth, more software enabled functions, upgrading from 2 to 4 channels at the same cost? If so, how often?

In the computer industry, manufacturers upgrade every year. How about the scope industry?

I have looked at videos of rigol, Keysight and GW Instek scopes. I seem to look the Keysight's UI the most.

[nctnico]

Don't let looks fool you! For my Agilent DSO7104A I really need the manual to operate it while the same functions are self explainatory on my GW Instek GDS-2204E. Setting the decoding thresholds is a good example.

[Keysight DanielBogdanoff]

It looks like these InfiniVision scopes have been around for a few years. Heard anything about possible upgrade in the near future?

DSOX2k, DSOX3k and DSOX4k (and their MSO variants) still sell very well. The DSOX6004 doesn't, though (but that shouldn't really surprise anyone considering in what scope class Keysight tries to compete with essentially a blown-up entry-level scope).

The 6000 X-Series had a bit of a slow start, but it does pretty well. It starts at 1 GHz instead of 200 MHz or lower like the rest of the InfiniiVision family, so a lot of people rule it out from the beginning because they don't want that much bandwidth.

And as long as the InfiniVision scopes sell well there's no need for Keysight to invest in a successor.

We definitely are investing in the future of scopes, if we wait until sales slow down to start a new ASIC we'll be in serious trouble. I'm also definitely not hinting at anything here, to design a custom ASIC and build a scope around it takes a long time.

[eeguy]

Do oscilloscope companies such as Keysight offer Christmas/Boxing Day Sales?

[AR]

This is obviously a question for Keysight , how long does it take to go from concept to new product in the market.

[TheSteve]

Do oscilloscope companies such as Keysight offer Christmas/Boxing Day Sales?

It is pretty safe to say no, they don't.

If you want a Keysight product the simple solution is to buy a used one off of ebay/craigslist/a test equipment reseller etc. The 2000 and 3000 series scopes are great and have a 3/5 year warranty. So most used ones(but not all) will still have factory warranty. I bought my DSOX3014A from the Keysight ebay store for the same price the average one goes for used. If you buy it used for a fair price the value isn't dropping very fast and someone else has already eaten the major depreciation.

[Keysight DanielBogdanoff]

Do oscilloscope companies such as Keysight offer Christmas/Boxing Day Sales?

Generally we don't. We trend towards longer promotions instead of 1-day sale event type activities. It's significantly easier to implement this type of thing when you aren't selling products through a distributor.

[Wuerstchenhund]

The 6000 X-Series had a bit of a slow start, but it does pretty well. It starts at 1 GHz instead of 200 MHz or lower like the rest of the InfiniiVision family, so a lot of people rule it out from the beginning because they don't want that much bandwidth.

I'm very sure it's more like people rule them out because they offer very little in a scope class where customers expect a lot more. Which is the reason Keysight offered pretty huge incentive specifically to the DSOX6004 to anyone who would aks (and evn those that didn't).

And as long as the InfiniVision scopes sell well there's no need for Keysight to invest in a successor.

We definitely are investing in the future of scopes, if we wait until sales slow down to start a new ASIC we'll be in serious trouble. I'm also definitely not hinting at anything here, to design a custom ASIC and build a scope around it takes a long time.

Indeed. I also didn't want to suggest that KS would sit on their hands or twiddling thumbs, which would be silly (i'd fully expect you to be already work on the foundation for the next generation scopes), what I meant was that there is little point in coming up with a successor if the existing product still sells well.

[Wuerstchenhund]

If you want a Keysight product the simple solution is to buy a used one off of ebay/craigslist/a test equipment reseller etc. The 2000 and 3000 series scopes are great and have a 3/5 year warranty. So most used ones(but not all) will still have factory warranty. I bought my DSOX3014A from the Keysight ebay store for the same price the average one goes for used. If you buy it used for a fair price the value isn't dropping very fast and someone else has already eaten the major depreciation.

I fully agree, you can save a lot of money with a used instrument.

As to warranty, be careful, I think it's only CertiPrime instruments that carry the full warranty, everything else comes with I think 30 days only. You can still buy additional warranty (KS calls it a 'repair agreement') as you can do for any KS instrument that is still in mainstream support, but that costs extra (but usually a lot less than people assume).

For younger Agilent/Keysight stuff, just look for a good offer on ebay (not sure I'd trust Craig's List, and test equipment resellers usually want insane amounts for their stuff), buy a repair agreement, and you've got pretty much the same protection as for a new product at a much lower price.

I've done this for lots of Agilent/Keysight gear, including my personal 33522B AWG and E3632A PSU.

[nfmax]

I combined a 'special offer' on the APPBNDL software options bundle with a CertiPrime deal on a distributor's ex-demo Agilent MSOX2024, when the branding changed to Keysight. Five years warranty. There really is no need to pay full list price unless you want to. This situation is a right PITA - it would be much better if everyone quoted more realistic prices, as they do at the hobbyist scope level, but I guess we are stuck with it now.

[EEVblog]

I'd be very surprised if they haven't been working on the Megazoon V (or whatever) for many years now.
But this stuff takes a long time to get to market. I think in another thread the average time between Megazoom releases has been 7 years? So still some way to go yet I suspect.
"Within a few months"? I doubt it, I suspect their sales are still reasonably solid.
And as Wuerstchenhund said, the 3000T was the upgrade to the 3000, although that may have been a bit of a stop-gap model maybe?

[eeguy]

I heard some bad experiences buying used equipment. If I am going to buy a scope, it will be brand new one. In case of buying the 2000, 3000T X-Series, when would be the best time to do so? The current offer on Keysight's website is buying the MSO at the cost of DSO if the scope is the 3K series or above. I am not sure if I will use the logic analyzer. What kind of software would be good to get? Can those software be included for free as a deal? Will there be education discount for those who buy it in North America? I guess I can wait for about half a year but no longer than that.  When was the 3000T released?

[Wuerstchenhund]

I heard some bad experiences buying used equipment.

I heard some pretty bad experiences buying new gear, too. That doesn't mean it's the norm.

Believe me, I buy a lot (and I mean, really a lot) test gear each year, in excess of $100k, and a lot of that is used. The occasions where I had problems I can count on one hand.

If I am going to buy a scope, it will be brand new one.

Why not. Just be prepared to pay a lot more then.

In case of buying the 2000, 3000T X-Series, when would be the best time to do so?

The best time is when you need the scope. Buy too late and you waste valuable time, buy too soon and you're sitting on dead capital.

The current offer on Keysight's website is buying the MSO at the cost of DSO if the scope is the 3K series or above. I am not sure if I will use the logic analyzer.

Then just don't use it. If they give you MSO for free, what's wrong with that?

What kind of software would be good to get?

The kind of software that you will be using on your projects. You should know yourself which one that is.

Can those software be included for free as a deal?

Ask keysight. If you pay RRP for the scope I'm sure they'll throw all kind of options in the basket.

When was the 3000T released?

As I said already, in 2014.

[nctnico]

I heard some bad experiences buying used equipment.

I heard some pretty bad experiences buying new gear, too. That doesn't mean it's the norm.

I agree. I think I have just as many bad experiences with new gear and used gear. Still I think buying something used needs more care by reading about common issues, recalls, etc. It is just like buying a car. You can buy used but you need to look under the hood and know what to look for. OTOH a new car can be a Monday morning model and quit working out every new moon. Depending on the seller's idea of service it may need some arm wrestling to get what is yours.

[eeguy]

The current offer on Keysight's website is buying the MSO at the cost of DSO if the scope is the 3K series or above. I am not sure if I will use the logic analyzer.

I hope that they could have another offer that suits more of my needs. For example, Tetronix has an offer of more bandwidth.

[Wuerstchenhund]

The current offer on Keysight's website is buying the MSO at the cost of DSO if the scope is the 3K series or above. I am not sure if I will use the logic analyzer.

I hope that they could have another offer that suits more of my needs. For example, Tetronix has an offer of more bandwidth.

Why don't you buy the Tektronix then?

[memset]

I'd be very surprised if they haven't been working on the Megazoon V (or whatever) for many years now.

In case we talk about embedded scopes, they seem to be build around custom ADC and custom acq/visualizer ASIC's.

Even the very recent 3000T is build on 13-years old ADC (Talon from year 2003) and DDR2-based Megazoom (IV?) ASIC. Obviously, both key components are somewhat outdated.

That's a nice way of use of mature components in low/mid level products, but Agilent is forced to spend two ADCs/ASICs to build 4-channel models with decent specifications.

I think the next round of 3000/4000-series replacement may utilize one for 4 channels, full or cutdown variant of 20GSa/s 10bit ADC currently found in DSOS series with some new single chip visualizer. I'd bet for replacement announce in year 2018 or even later with a range of 200 MHz - 2.5GHz+ of pure software license-limited bandwidth with 10GSa/s to 20GSa/s sample rate.
If they'll go more conservative and greedy way, ADC would be 8 bit from DSO9000-series, not 10 bit from DSOS.

[Hydrawerk]

I think that Tek MSO2000 has not been upgraded since 2008. http://www.tek.com/oscilloscope/mso2000-dpo2000

[Someone]

Even the very recent 3000T is build on 13-years old ADC (Talon from year 2003) and DDR2-based Megazoom (IV?) ASIC. Obviously, both key components are somewhat outdated.

Do you have a reference for that? The memory is embedded on the megazoom IV ASIC (and likely has a similar amount if not more video memory than acquisition memory) but is it a DDR2 cell?

[Gandalf_Sr]

As Steve has already stated, Keysight have their own store on eBay where you can buy used equipment for way less than list price with either a full warranty or a 30 day warranty, I bought my MSO7104 there for a fraction of the new price.

[Faith]

I hope that they could have another offer that suits more of my needs. For example, Tetronix has an offer of more bandwidth.

As I and many others have mentioned before (both in this thread and one of your previous ones); there's many promotions to be had if you're willing to look for them. See:

If that's the route you're going to take however I would recommend buying it from Keysight's Premium Used store on eBay.

From over there the top-of-the-line MSOX2024A (200MHz 4+8 Channel) costs less than the MSOX2002A (70MHz 2+8 Channel) would if you were to buy it "new."

The MSOX2024A which I borrow on occasion was purchased from there and it really is indistinguishable from a used unit. It's thoroughly refurbished and comes with new calibration and new five-year warranty.

Just to clarify the MSOX2024A is US$1,975.05 on Keysight's Premium Used eBay store whereas its list price is normally US$3,591.00 (prior to any promotions or further discounts).

If you are adamant on buying Keysight then that's one option. Another option would be to buy the MSOX3104T (1GHz 4+8 Channel) also from their Premium Used store on eBay for US$6,584.00 (list price is US$16,025).

Given those offers (amongst others which appear from time to time) it doesn't really make any sense at all to pay whatever the list price is.

[Faith]

Also I should add that with regards to the MSOX3104T if you absolutely do not need the bandwidth then any promotion becomes kinda moot as well.

For myself I would rather pay list price for the MSOX3024T than get the MSOX3104T at a third of the price because the MSOX3024T is still cheaper and for my case at least I know that I do not require the 1GHz bandwidth.

And once you're looking at oscilloscopes in this pricing territory I'd seriously consider taking a page from Wuerstchenhund's book if I were you and look at the Teledyne LeCroy WaveSurfer 3000.

Even if you still end up buying Keysight it's a good to know what's out there and it's also a good negotiation tool whenever you mention Keysight to LeCroy and LeCroy to Keysight.

At the end of the day only you can decide what's best for the work you require. Given the nature of your questions though you really ought to ask yourself whether you really need an oscilloscope at this point of time. Especially one in this price class.

You'd be surprised at how much you can debug without one especially in the realm of "robotics research" (as per your original thread).

Back when I used to program a lot in C my applications would be riddled with loads of debug-related printf()'s which could be globally enabled/disabled by a DEFINE.

[LabSpokane]

If you know what you want, just contact Oliver via the Keysight eBay store and tell him.  Within reason, he will bundle things up the way you want, even including a one year warranty on certain items (for a fee). 

[Wuerstchenhund]

I think the next round of 3000/4000-series replacement may utilize one for 4 channels, full or cutdown variant of 20GSa/s 10bit ADC currently found in DSOS series with some new single chip visualizer. I'd bet for replacement announce in year 2018 or even later with a range of 200 MHz - 2.5GHz+ of pure software license-limited bandwidth with 10GSa/s to 20GSa/s sample rate.
If they'll go more conservative and greedy way, ADC would be 8 bit from DSO9000-series, not 10 bit from DSOS.

That is extremely unlikely, for various reasons. One of that is cost because 10+GS/s ADC hybrids aren't exactly cheap, and the 10bit variants a lot less so (a single hybrid from the DSO-S alone costs them probably as much as a complete DSOX3kT to make).

Also, it would be pretty idiotic to put 10GSa/s or 20GSa/s hybrids in entry-level scopes with bandwidths of 1GHz and less where such excessive sample rates have zero benefit.

[Wuerstchenhund]

Even the very recent 3000T is build on 13-years old ADC (Talon from year 2003) and DDR2-based Megazoom (IV?) ASIC. Obviously, both key components are somewhat outdated.

Do you have a reference for that? The memory is embedded on the megazoom IV ASIC (and likely has a similar amount if not more video memory than acquisition memory) but is it a DDR2 cell?

I think Daniel from Keysight mentioned in another thread that the MegaZoom IV memory is indeed DDR2.

[Someone]

Even the very recent 3000T is build on 13-years old ADC (Talon from year 2003) and DDR2-based Megazoom (IV?) ASIC. Obviously, both key components are somewhat outdated.

Do you have a reference for that? The memory is embedded on the megazoom IV ASIC (and likely has a similar amount if not more video memory than acquisition memory) but is it a DDR2 cell?

I think Daniel from Keysight mentioned in another thread that the MegaZoom IV memory is indeed DDR2.

Its not in the forum search function of all Daniels posts, and there are no matches on google hence the wondering about the source.

[Wuerstchenhund]

Even the very recent 3000T is build on 13-years old ADC (Talon from year 2003) and DDR2-based Megazoom (IV?) ASIC. Obviously, both key components are somewhat outdated.

Do you have a reference for that? The memory is embedded on the megazoom IV ASIC (and likely has a similar amount if not more video memory than acquisition memory) but is it a DDR2 cell?

I think Daniel from Keysight mentioned in another thread that the MegaZoom IV memory is indeed DDR2.

Its not in the forum search function of all Daniels posts, and there are no matches on google hence the wondering about the source.

I found the thread:

https://www.eevblog.com/forum/testgear/comparing-agilent-infiniivision-2000-and-3000-x-series-oscilloscopes/?all

Although it seems Daniel only mentioned DDR.

[Someone]

Even the very recent 3000T is build on 13-years old ADC (Talon from year 2003) and DDR2-based Megazoom (IV?) ASIC. Obviously, both key components are somewhat outdated.

Do you have a reference for that? The memory is embedded on the megazoom IV ASIC (and likely has a similar amount if not more video memory than acquisition memory) but is it a DDR2 cell?

I think Daniel from Keysight mentioned in another thread that the MegaZoom IV memory is indeed DDR2.

Its not in the forum search function of all Daniels posts, and there are no matches on google hence the wondering about the source.

I found the thread:

https://www.eevblog.com/forum/testgear/comparing-agilent-infiniivision-2000-and-3000-x-series-oscilloscopes/?all

Although it seems Daniel only mentioned DDR.

Which is not describing whats in the current ASIC but what alternatives might be.

[EEVblog]

And once you're looking at oscilloscopes in this pricing territory I'd seriously consider taking a page from Wuerstchenhund's book if I were you and look at the Teledyne LeCroy WaveSurfer 3000.

You mean Siglent SDS3000 

[Faith]

And once you're looking at oscilloscopes in this pricing territory I'd seriously consider taking a page from Wuerstchenhund's book if I were you and look at the Teledyne LeCroy WaveSurfer 3000.

You mean Siglent SDS3000 

Hahaha. I was actually wondering a couple of days ago whether or not the WaveSurfer 3000 also suffers from Siglent's (in?)famous "rust." I couldn't find any teardown photos or videos anywhere however >,<"...

And to eeguy; just to make life a little more interesting for you, have a look at the Rohde & Schwarz RTM.

Rohde & Schwarz are also having some sort of Mixed Signal promotion of their own until the end of the year which also includes licenses.

[tautech]

And once you're looking at oscilloscopes in this pricing territory I'd seriously consider taking a page from Wuerstchenhund's book if I were you and look at the Teledyne LeCroy WaveSurfer 3000.

You mean Siglent SDS3000 

Not sure what point you're trying to make Dave but yes the HW is made by Siglent but both the SDS3k and the WS3k are formally a joint effort development between Siglent and LeCroy.

First revealed here by rf-loop:
https://www.eevblog.com/forum/testgear/siglent's-new-products-sds3000-series-oscilloscopes/

[Gandalf_Sr]

One extra bit of information, if you're considering a purchase from Keysight's eBay store, is that all their listings seem to include a 'Best Offer' option and many people have found, myself included, that they will accept an offer that's 10% less than their asking price.

One other thing to consider is the probes because, when buying from the Keysight eBay store, you don't get any.  You can pick up used probes on eBay but go carefully because it's a bit of a crap shoot on serviceability; I've bought some that didn't work but, overall, it's been worthwhile - I now own a full range of probes that cover most of my needs.

[Faith]

One other thing to consider is the probes because, when buying from the Keysight eBay store, you don't get any.  You can pick up used probes on eBay but go carefully because it's a bit of a crap shoot on serviceability; I've bought some that didn't work but, overall, it's been worthwhile - I now own a full range of probes that cover most of my needs.

You do get probes with items sold as "Premium Used." For all other items you'll have to check the item description.

[eeguy]

Even the very recent 3000T is build on 13-years old ADC (Talon from year 2003) and DDR2-based Megazoom (IV?) ASIC. Obviously, both key components are somewhat outdated.

Do you have a reference for that? The memory is embedded on the megazoom IV ASIC (and likely has a similar amount if not more video memory than acquisition memory) but is it a DDR2 cell?

I read somewhere in the forum that although the 2000, 3000T X-Series oscilloscopes have less memory than scopes of other brands that are cheaper, the memory of the Keysight oscilloscopes are sufficient (or better?) because of some kind of efficient hardware implementation and ASIC. Is that right?

I think Daniel from Keysight mentioned in another thread that the MegaZoom IV memory is indeed DDR2.

Its not in the forum search function of all Daniels posts, and there are no matches on google hence the wondering about the source.

I found the thread:

https://www.eevblog.com/forum/testgear/comparing-agilent-infiniivision-2000-and-3000-x-series-oscilloscopes/?all

Although it seems Daniel only mentioned DDR.

Which is not describing whats in the current ASIC but what alternatives might be.

[Wuerstchenhund]

Even the very recent 3000T is build on 13-years old ADC (Talon from year 2003) and DDR2-based Megazoom (IV?) ASIC. Obviously, both key components are somewhat outdated.

Do you have a reference for that? The memory is embedded on the megazoom IV ASIC (and likely has a similar amount if not more video memory than acquisition memory) but is it a DDR2 cell?

I think Daniel from Keysight mentioned in another thread that the MegaZoom IV memory is indeed DDR2.

Its not in the forum search function of all Daniels posts, and there are no matches on google hence the wondering about the source.

I found the thread:

https://www.eevblog.com/forum/testgear/comparing-agilent-infiniivision-2000-and-3000-x-series-oscilloscopes/?all

Although it seems Daniel only mentioned DDR.

Which is not describing whats in the current ASIC but what alternatives might be.

Then ask Daniel. He's at the soruce and I'm sure will happily tell you or try to find out for you.

I'd be surprised if it wasn't DDR2, though.

[EEVblog]

Not sure what point you're trying to make Dave but yes the HW is made by Siglent but both the SDS3k and the WS3k are formally a joint effort development between Siglent and LeCroy.

It's a Siglent rebadger, I was told that today by R&S themselves. But yes, LeCroy had some input, probably on par with Keysight helping with Rigol's scopes they rebadged, which I believe wasn't a huge amount.

[memset]

Do you have a reference for that? The memory is embedded on the megazoom IV ASIC (and likely has a similar amount if not more video memory than acquisition memory) but is it a DDR2 cell?

Embedded ASIC memory should be SRAM. But inside DSOX you can find one DDR2 chip connected to each Megazoom ASIC. I have no idea for that type of buffer it is used for.

[memset]

Also, it would be pretty idiotic to put 10GSa/s or 20GSa/s hybrids in entry-level scopes with bandwidths of 1GHz and less where such excessive sample rates have zero benefit.

Not in year 2018+. Isn't it idiotic to put 5GSa/s ADC into 100MHz DSOX3014T?

Also, ADC is just a CMOS chip (okay, two chips MCM for 10-bit DSOS ADC). The more of them you make, the less each one costs.
I think in several years DSOX3000/DSOX4000 replacement should be up to 2,5GHz or even up to 5GHz BW. MSOY3254A.

[Wuerstchenhund]

Also, it would be pretty idiotic to put 10GSa/s or 20GSa/s hybrids in entry-level scopes with bandwidths of 1GHz and less where such excessive sample rates have zero benefit.

Not in year 2018+. Isn't it idiotic to put 5GSa/s ADC into 100MHz DSOX3014T?

Not when the scope series offers bandwidths up to 1GHz, which the DSOX3000 Series does. Also, the DSOX3000T is pretty much a DSOX4000A in a smaller case and with smaller screen, and that one goes to 1.5GHz, hence the 5GSa/s sample rate. Using the same front end and acquisition system on the DSOX3kT reduces costs and gives the DSOX3kT additional features over the DSOX3kA.

There is absolutely no point putting a 10GSa/s+ hybrid in a scope that has a max BW of 1GHz (or even 1.5GHz for that matter). All it does is using up available sample memory faster, without providing even the slightest benefit to the user.

I doubt any sane engineer would do that.

Also, ADC is just a CMOS chip (okay, two chips MCM for 10-bit DSOS ADC). The more of them you make, the less each one costs.

Not as much as you think. Plus the costs only go down after you've produced a large number, which means there'd be a pretty high initial outlay that KS would have to carry.

I think in several years DSOX3000/DSOX4000 replacement should be up to 2,5GHz or even up to 5GHz BW. MSOY3254A.

Again, that's extremely unlikely. The bandwidths haven't really changed in the last 20+ years, 100Mhz was entry-level back then as it was today, and 500/600MHz is still pretty much the general limit of the entry-level segment, and 1GHz/1.5Ghz the upper limit of the mid-range segment. And that is for a reason, because the general bandwidth requirements for entry-level and mid-range classes haven't changed dramatically over the years (high-end on the other side has, quite dramatically so), and there is no sign that this will be different in the next 10 years or so.

The successor of the DSOX3kT will most certainly still cover BWs up to 1GHz, and it's successor will also still cover BWs up to 1GHz, and so on.

I'm sorry but none of your ideas have any roots in reality.

[nctnico]

With high speed busses and things like wireless data links becoming more common I have to disagree that 100MHz is will stay entry level and 1GHz is on the high end range. It wouldn't surprise me if 1GHz+ is standard in a few years when you look slightly above the low end segment.

[Wuerstchenhund]

With high speed busses and things like wireless data links becoming more common I have to disagree that 100MHz is will stay entry level and 1GHz is on the high end range. It wouldn't surprise me if 1GHz+ is standard in a few years when you look slightly above the low end segment.

1GHz is already in the top end of the upper mid-range, and pretty much the entry into the high end segment. And I very much doubt that this will change much in the years to come, for various reasons.

First, even if you assume that high speed 20+GSa/s ADCs will become dirt cheap in the near future (which is very unlikely), a multi-GHz front end isn't exactly cheap either. Plus, with the amount of data the scope has to process at least quadrupled, you'll need a much stronger processing backend. There's a reason why high bandwidth scopes are huge and full of fans, and it's extremely optimitic to think that the same processing power will be doable in a $20 low-power embedded platform in only a few years.

Also, even when assuming that all that is solved (which I doubt very much), a 1GHz+ scope still requires a 1+GHz probing solution which alone costs north of $2k per channel, and the costs for that aren't going away anytime soon. 1Ghz actually isn't too bad but a bit higher and probing can get really excessive, both effort and cost-wise. It's extremely unlikely that this will reach entry-level budget in a few years, or pretty much ever. And what's the hobbyist going to do with a multi-GHz scope and no probes?

I also disagree that a few years down the road hobbyists will be requiring 1+GHz bandwidth. Most hobbyist projects are fine with existing standard busses (RS-232/485, I2C, SPI, CAN, LIN, FlexRay, 10/100Mbps Ethernet), and I can't see that changing for the forseeable future. And where faster communication standards are needed, hobbyists are far better off by buying ready-made pre-qualified communication blocks (like the ones you can buy for WiFi or GSM) instead of developing a multi-GHz solution on their own (something that even for more experienced engineers isn't exactly a cakewalk, RF can be devil-ish) and buying multi-GHz gear plus probing solution to test that.

[nctnico]

Having a higher bandwidth also means needing a better probing solution otherwise you are just looking at how the probe distorts the signal. Fortunately high frequency probing doesn't have to be expensive. There is a lot out there on the second hand market like passive divider RF probes and you can always choose to create dedicated signal taps on a prototype. At some point frequency you can't stick a needle onto a trace or pad and expect to get something meaningfull on the display so the solution with the signal taps is the way to go. The cost is a few resistors, maybe an extra amplifier and an RF connector.

[Wuerstchenhund]

Truth be told, without very special probes, looking at signal >50MHz with any kind of fidelity is extremely difficult.  I'm not saying you can't do it, but it is difficult and requires training of the operator to get it right, and use of special probe accessories.  Above 300MHz is again another order of magnitude of difficulty.  I work mainly with analog, digital, and some RF.  Why did I buy a 1GHz MSOX3000A?  One word: Resolution.  I want to have as many samples of the signal I'm looking at as possible in order to get a better idea of what I'm looking at-- so, at the higher frequencies in the Mixed-Signal embedded systems work I do, the 5GHz sample rate is fantastic!

Not sure what you mean with "resolution". The MSOX is a typical 8bit scope, and offers exactly the same resolution as any other 8bit DSO.

If you're talking about horizontal resolution, well then just because the scope samples at 5GHz (5GSa/s) doesn't mean you get "5GHz resolution" (200ps). You won't, and with a 1Ghz BW you'll probably get less than half of that (400ps).
 
Also, I assume you also use a proper 1+Ghz active probes or at least a Low Zo passive probe, not the standard N2890A 500Mhz passive probes that come with it? Because if not then what you see on the screen might have little to do with the actual signal.

[Someone]

Also, it would be pretty idiotic to put 10GSa/s or 20GSa/s hybrids in entry-level scopes with bandwidths of 1GHz and less where such excessive sample rates have zero benefit.

Not in year 2018+. Isn't it idiotic to put 5GSa/s ADC into 100MHz DSOX3014T?

Not when the scope series offers bandwidths up to 1GHz, which the DSOX3000 Series does. Also, the DSOX3000T is pretty much a DSOX4000A in a smaller case and with smaller screen, and that one goes to 1.5GHz, hence the 5GSa/s sample rate. Using the same front end and acquisition system on the DSOX3kT reduces costs and gives the DSOX3kT additional features over the DSOX3kA.

There is absolutely no point putting a 10GSa/s+ hybrid in a scope that has a max BW of 1GHz (or even 1.5GHz for that matter). All it does is using up available sample memory faster, without providing even the slightest benefit to the user.

I doubt any sane engineer would do that.

Except that the current 8 bit 4GSa/s ADCs with an ENOB of 7 are actually the combined result of 32 interleaved 12 bit ADCs running at 125MHz each (http://poulton.net/papers.public/2002isscc_10_1_tal_slides.pdf). Assuming a similar ADC with an ENOB of 6.6 at 20GSa/s being 80 interleaved 12 bit ADCs running at 250MHz each (http://poulton.net/papers.public/2002isscc_10_1_tal_slides.pdf) instead of phasing them for maximum sample rate you could realign them into groups of 4 for a 5GSa/s ADC with an ENOB of 7.6. Expand that forward to newer technology and adding higher sampling rates well beyond the Nyquist requirement has practical applications if interleaved for resolution rather than full sample rate. Engineering can be fun!

[tautech]

Not sure what point you're trying to make Dave but yes the HW is made by Siglent but both the SDS3k and the WS3k are formally a joint effort development between Siglent and LeCroy.

It's a Siglent rebadger, I was told that today by R&S themselves. But yes, LeCroy had some input, probably on par with Keysight helping with Rigol's scopes they rebadged, which I believe wasn't a huge amount.

Rebadged it may be, but with one big difference, it is only available to the western world as a LeCroy WS3k. Period.

[nctnico]

Not sure what point you're trying to make Dave but yes the HW is made by Siglent but both the SDS3k and the WS3k are formally a joint effort development between Siglent and LeCroy.

It's a Siglent rebadger, I was told that today by R&S themselves. But yes, LeCroy had some input, probably on par with Keysight helping with Rigol's scopes they rebadged, which I believe wasn't a huge amount.

I really doubt R&S is a good source for that kind of information  It has been known for a while that Siglent designed the hardware and Lecroy made the firmware (for obvious reasons).

[Wuerstchenhund]

It's a Siglent rebadger, I was told that today by R&S themselves.

Really, you believe what a R&S guy says about a competitor's scope? Seriously? 

Whom do you ask about Keysight scopes then? A Tektronix guy? 

But yes, LeCroy had some input, probably on par with Keysight helping with Rigol's scopes they rebadged, which I believe wasn't a huge amount.

You're wrong. As tautech said, the SDS3000/WS3000 is a co-development between LeCroy and Siglent where both parties share the hardware responsibility, Siglent carries manufacturing responsibility and LeCroy carries the software responsibility.

Such co-operations aren't new to LeCroy, who did them in the past with other companies like Iwatsu (the whole WaveRunner(2) LT/Wavepro 900 Series was developed that way, again with LeCroy and Iwatsu sharing hardware responsibility, Iwatsu production and LeCroy software).

It's quite a bit different to Agilent helping Rigol, a company that back then had very little experience designing DSOs, to get the worst issues sorted, and then pretty much leave the scope design and firmware to Rigol, and then just buying re-badged scopes for selling them as Agilent. There's actually a lot of LeCroy IP in that WS3000 (it's a X-Stream Lite scope so it uses LeCroy's X-Stream architecture instead of one based on proprietary ASICs as on other scopes, plus it comes with MAUI and a few other proprietary features from their high end scopes). IP LeCroy is pretty protective about (for obvious reasons).

LeCroy does re-badging, too, everything in their entry-level segment is rebadged stuff from Iwatsu or Siglent. Mostly because they don't really care about that segment of the market.

[jpk42]

If you know what you want, just contact Oliver via the Keysight eBay store and tell him.  Within reason, he will bundle things up the way you want, even including a one year warranty on certain items (for a fee).

Is this true? I'm after a DSOX2014 or equivalent (4 channels, 70-200MHz range, no digital channels required) either used or premium used. Keysight have DSOX2012's under used on their ebay, however I would prefer 4 channels....

[Keysight DanielBogdanoff]

If you know what you want, just contact Oliver via the Keysight eBay store and tell him.  Within reason, he will bundle things up the way you want, even including a one year warranty on certain items (for a fee).

Is this true? I'm after a DSOX2014 or equivalent (4 channels, 70-200MHz range, no digital channels required) either used or premium used. Keysight have DSOX2012's under used on their ebay, however I would prefer 4 channels....

You can always ask - their stock is always in flux and they generally have a pretty good idea of what's coming to them. They also potentially have some flexibility when it comes to licensing (options, DSO vs. MSO, etc.). While I can't talk about pricing or anything like that, I always tell people it never hurts to try!

[TheSteve]

If you know what you want, just contact Oliver via the Keysight eBay store and tell him.  Within reason, he will bundle things up the way you want, even including a one year warranty on certain items (for a fee).

Is this true? I'm after a DSOX2014 or equivalent (4 channels, 70-200MHz range, no digital channels required) either used or premium used. Keysight have DSOX2012's under used on their ebay, however I would prefer 4 channels....

As Daniel just said it never hurts to ask. You can and should negotiate with them. When I wanted a 3000 series scope I had to wait a bit but when one came up I grabbed it for a great price.

[tautech]

If you know what you want, just contact Oliver via the Keysight eBay store and tell him.  Within reason, he will bundle things up the way you want, even including a one year warranty on certain items (for a fee).

Is this true? I'm after a DSOX2014 or equivalent (4 channels, 70-200MHz range, no digital channels required) either used or premium used. Keysight have DSOX2012's under used on their ebay, however I would prefer 4 channels....

Shame you weren't a few weeks earlier, I've just sold my fully optioned SDS2304 demo unit (no MSO) and as you're sort of local to me......

[LabSpokane]

If you know what you want, just contact Oliver via the Keysight eBay store and tell him.  Within reason, he will bundle things up the way you want, even including a one year warranty on certain items (for a fee).

Is this true? I'm after a DSOX2014 or equivalent (4 channels, 70-200MHz range, no digital channels required) either used or premium used. Keysight have DSOX2012's under used on their ebay, however I would prefer 4 channels....

It's true. There are multiple locations that equipment can be pulled from and Keysight is usually happy to work with folks like us, even though our needs may be modest.

[jpk42]

Great to hear. I will try this avenue out. Thanks.

[Wuerstchenhund]

First, I don't work with 500MHz signals.  At most, I will look at <=50MHz signals in my embedded systems work.  Some of the analog stuff can go 2-3 times higher than that on rare occasions.  The RF stuff is mainly for "indication"-- with no hope of getting any kind of accuracy-- I use my 22GHz spectrum analyzer for that if I need it.

Second, yes, I meant horizontal resolution.  Been using scopes for 40 years, so I "get it".  There are only a few situations where 5GHz sampling is used, and when I need it, I have it.  Using delay triggering, I can look at a fairly fast signal and still get plenty of horizontal resolution.  Keysight scopes are pretty good at reconstructing the signal, but more data points per unit of time always helps make the trace more accurate.

I'm sorry but that is not true. Once you satisfy Nyquist-Shannon (f_s>2xF₀) then increasing the sample rate does not add any more information or increase accuracy on a modern scope using sin(x)/x interpolation in normal acquisition. All you do is filling up the memory with "empty" data points (there's a use of sample rates higher than Nyquist-Shannon to compensate for excess BW, something which every scope has, to prevent aliasing, and for oversampling techniques to increse the vertical resolution; none of that adds to horizontal resolution, though).

Your 1GHz MSOX3104 has a spec'd rise time of 450ps which suggests a steep roll off of the BW limiting filter (c=0.45), which is much higher than the time resolution (200ps) of a 5GSa/s sampling system and therefore your (first) limiting factor in what time resolution you actually get.

Third, yes I use the 500MHz probes that came with the scope, and yes I'm smart enough to understand that these are the limitation to signal fidelity on the high end.  This does not stop me from using the full timing bandwidth for time differences between two signals.

Yes, it actually does stop you. The N2890A 500MHz passive probe has a rise time of 700ps which is even higher than the one of your scope. Since your scope doesn't have a Gaussian rolloff the system BW and system risetime isn't easy to determine, but it'll be worse than the lowest common denominator (which is the probe at 500Mhz/700ps).

Now you said you're only looking at signals of up to 50MHz. If that is a non-sinoid waveform, for example a square wave, then you'll already need 450MHz BW to get a somewhat true representation of the signal (9th harmonics), which may well run into the systemic limitations of your scope + probe.

As to the time resolution, since your system risetime is at least 700ps you won't get any better time resolution than this, no matter what sample rate.

I can also make my own field-expedient probes for super high frequency using a piece of miniature coax (RG316?) and a RF-capable metal film resistor--- the scope manual shows how to do this. 

I doubt the MXOS3000A manual states how you can build a SHF (that's 3Ghz to 30Ghz) probes, for which RG316 or similar cables with a BW <3Ghz are hardly adequate anyways. However, even self-made RF probes, like all probes, suffer from similar systemic limitations. And even with the best probe you'dd not get a better time resolution than the ~1Ghz (450ps).

I can't afford (at this time) better probes, if I could, I would buy them for certain.  Remember, it's not how big your probe is, but rather it's what you do with it that counts...   

It's also very much about understanding the complete system of scope + probe, and the various inherent limitations. Otherwise you might end up assuming a precision or resolution that just isn't there.

[G0HZU]

First, I don't work with 500MHz signals.  At most, I will look at <=50MHz signals in my embedded systems work.  Some of the analog stuff can go 2-3 times higher than that on rare occasions.  The RF stuff is mainly for "indication"-- with no hope of getting any kind of accuracy-- I use my 22GHz spectrum analyzer for that if I need it.

Second, yes, I meant horizontal resolution.  Been using scopes for 40 years, so I "get it".  There are only a few situations where 5GHz sampling is used, and when I need it, I have it.  Using delay triggering, I can look at a fairly fast signal and still get plenty of horizontal resolution.  Keysight scopes are pretty good at reconstructing the signal, but more data points per unit of time always helps make the trace more accurate.

I'm sorry but that is not true. Once you satisfy Nyquist-Shannon (f_s>2xF₀) then increasing the sample rate does not add any more information or increase accuracy on a modern scope using sin(x)/x interpolation in normal acquisition. All you do is filling up the memory with "empty" data points (there's a use of sample rates higher than Nyquist-Shannon to compensate for excess BW, something which every scope has, to prevent aliasing, and for oversampling techniques to increse the vertical resolution; none of that adds to horizontal resolution, though).

Your 1GHz MSOX3104 has a spec'd rise time of 450ps which suggests a steep roll off of the BW limiting filter (c=0.45), which is much higher than the time resolution (200ps) of a 5GSa/s sampling system and therefore your (first) limiting factor in what time resolution you actually get.

Third, yes I use the 500MHz probes that came with the scope, and yes I'm smart enough to understand that these are the limitation to signal fidelity on the high end.  This does not stop me from using the full timing bandwidth for time differences between two signals.

Yes, it actually does stop you. The N2890A 500MHz passive probe has a rise time of 700ps which is even higher than the one of your scope. Since your scope doesn't have a Gaussian rolloff the system BW and system risetime isn't easy to determine, but it'll be worse than the lowest common denominator (which is the probe at 500Mhz/700ps).

Now you said you're only looking at signals of up to 50MHz. If that is a non-sinoid waveform, for example a square wave, then you'll already need 450MHz BW to get a somewhat true representation of the signal (9th harmonics), which may well run into the systemic limitations of your scope + probe.

As to the time resolution, since your system risetime is at least 700ps you won't get any better time resolution than this, no matter what sample rate.

I can also make my own field-expedient probes for super high frequency using a piece of miniature coax (RG316?) and a RF-capable metal film resistor--- the scope manual shows how to do this. 

I doubt the MXOS3000A manual states how you can build a SHF (that's 3Ghz to 30Ghz) probes, for which RG316 or similar cables with a BW <3Ghz are hardly adequate anyways. However, even self-made RF probes, like all probes, suffer from similar systemic limitations. And even with the best probe you'dd not get a better time resolution than the ~1Ghz (450ps).

I can't afford (at this time) better probes, if I could, I would buy them for certain.  Remember, it's not how big your probe is, but rather it's what you do with it that counts...   

It's also very much about understanding the complete system of scope + probe, and the various inherent limitations. Otherwise you might end up assuming a precision or resolution that just isn't there.

Even my crappy/ancient HP54540C can measure timing differences that are a small fraction of the scope's risetime. A higher sample rate would help here especially with single shot measurements but it does OK here IMO.

[nctnico]

When you want to look at time differences you'll need to deskew (=adjust the horizontal time delay) your probes and first. I recall a situation where I used a scope to look at some ns timing on a digital bus and it was completely off. The next thing I thought was: 'crap I need to get some equal length BNC cables first before I can measure this'.

[Someone]

First, I don't work with 500MHz signals.  At most, I will look at <=50MHz signals in my embedded systems work.  Some of the analog stuff can go 2-3 times higher than that on rare occasions.  The RF stuff is mainly for "indication"-- with no hope of getting any kind of accuracy-- I use my 22GHz spectrum analyzer for that if I need it.

Second, yes, I meant horizontal resolution.  Been using scopes for 40 years, so I "get it".  There are only a few situations where 5GHz sampling is used, and when I need it, I have it.  Using delay triggering, I can look at a fairly fast signal and still get plenty of horizontal resolution.  Keysight scopes are pretty good at reconstructing the signal, but more data points per unit of time always helps make the trace more accurate.

I'm sorry but that is not true. Once you satisfy Nyquist-Shannon (f_s>2xF₀) then increasing the sample rate does not add any more information or increase accuracy on a modern scope using sin(x)/x interpolation in normal acquisition. All you do is filling up the memory with "empty" data points (there's a use of sample rates higher than Nyquist-Shannon to compensate for excess BW, something which every scope has, to prevent aliasing, and for oversampling techniques to increse the vertical resolution; none of that adds to horizontal resolution, though).

Your 1GHz MSOX3104 has a spec'd rise time of 450ps which suggests a steep roll off of the BW limiting filter (c=0.45), which is much higher than the time resolution (200ps) of a 5GSa/s sampling system and therefore your (first) limiting factor in what time resolution you actually get.

When you wish to measure relative phases or delays between events the additional sample rate does improve the resolution of the measurement. Consider the extreme of only just meeting Nyquist limit with 500MHz signal bandwidth for a 1GSa/s acquisition so you have 2 points in the edge transition and estimate the crossing of the threshold by reconstruction, bump the sample rate up to the maximum 5GSa/a and you now have 5 times more points to reconstruct the edge from reducing the noise in the measurement and improving its resolution.

[nctnico]

According to signal theory you won't get any extra information from 1Gs/s versus 5Gs/s if the bandwidth is the same in both situations.

[Someone]

According to signal theory you won't get any extra information from 1Gs/s versus 5Gs/s if the bandwidth is the same in both situations.

Thats assuming you have no noise on the sampling process, the real world is a little more complicated with noise in both the amplitude of the sample and the time of the sample (jitter and aperture). Adding additional samples allows the signal to noise ratio to be improved and the result can have both higher resolution and lower noise.

[Performa01]

Slow scope, 1.2ns rise time. Fully digital trigger system.

The same 400MHz signal fed into two channels via resistive power splitter and two cables (both RG58, hence velocity factor 0.66), one of them being about 40mm longer than the other. What time difference do we expect?



… and what does the scope measure?

The scope also measures the transition times of the input signal – and appears to be pretty accurate at that.

Btw. Triggering is also rock-stable without the slightest sign of jitter – which it better should, as we are about measuring time differences well below 1ns.

Here’s the quiz:

A) Which channel has the shorter cable connected?
B) How can a scope measure rise/fall times shorter than its own rise time?

… and here’s the challenge:

Demonstrate the same measurement on a scope with just 1GSa/s!

[Lukas]

When the input signal is reasonably band-limited, the sampling rate doesn't determine the delta time resolution. Since the transition will smooth out over two or more sample points, the sample values now carry timing information. That's how digital trigger works. For more information search for 'transition midpoint timing tdc'

[Someone]

When the input signal is reasonably band-limited, the sampling rate doesn't determine the delta time resolution. Since the transition will smooth out over two or more sample points, the sample values now carry timing information. That's how digital trigger works. For more information search for 'transition midpoint timing tdc'

Only in a noise free system, additional samples are reducing noise and increasing resolution.

[omgfire]

Nyquist theory is about transmitting data [1's and 0's], while I am more interested in what is going on in between [i.e., analog signals].

No, it is not.

All of this bullshit theoretical stuff is nonsense, and is contrary to my experience.  I have to go with my experience, and not some textbook bullshit about why I have been "doing it wrong" for 40 years.  My experience is that more data points per second is better.  Your mileage may vary.  Everyone has their own opinion, and some of us will have to agree to disagree.

Your opinion about math theorem does not matter. Mathematical theorems have mathematical proof.

[testmode]

Nyquist theory is about transmitting data [1's and 0's], while I am more interested in what is going on in between [i.e., analog signals].

No, it is not.

Agree.  And to elaborate, while Nyquist theorem is all about 1's and 0's, it is in fact about the digital representation of the underlying analog signal.  On the other hand, I have to agree as well that having a higher sampling rate than what is needed is not entirely useless at all because it could provide better fidelity for the converted signal.  Although one has to consider as well how much fidelity you actually need is entirely dependent on the intended application.

[nctnico]

It all depends on how good the reconstruction algorithm is. The thing is that according to Nyquist all information of the signal is there up to (but not including) fs/2. However if you LOOK at a sine wave which is close to fs/2 you'll only see a few seemingly random sample points. So in order to SEE the signal it has to be reconstructed and that is where reconstruction algorithms come into play. Still a higher than necessary samplerate doesn't add any extra information.

[jjoonathan]

I don't doubt the theorem. I doubt your ability to wield it.

These things usually come with a dozen assumptions, nitpicky details about types of continuity and convergence, and a slew of carefully worded definitions. Even if the theorem (or a suitably weakened form) is possible to apply to a physical system, and it's often not, it's at least impractical. Even if you do know the requisite math (likely: information and signal theory taught to a level requiring a background in real/complex analysis), physics, and a decent understanding of this theorem in particular, there's still plenty of room for surprise. Remember the Knuth quote "Beware of bugs in the above code, I've only proven it correct, I haven't actually run it." Same principle here.

For instance, several people here have mentioned noise -- your analog front end will not be able to infinitely attenuate out-of-band signals and even if it could your ADC does not have an infinitely low noise floor. If you can't make a truly band-limited signal, and you can't, the theorem doesn't apply. Its conclusion might still be true, or it might still be mostly true (i.e. you can find worst case reconstruction inaccuracy as a function of out-of-band noise), but you can't appeal to the original line of reasoning anymore.

The facts that 1: sample rate costs significant money (lots more than sinx/x interpolation, err, I mean "reconstruction algorithms") and 2: manufacturers regularly sample at >>2*BW (typically 4-10*BW) suggest that there's a bigger tradeoff at play. Here are the things we want but can't have simultaneously:

1. Full fs/2 bandwidth
2. Good step response
3. Good out-of-band signal rejection

Modern oscilloscopes sacrifice #1 to get #2 and #3. Last generation sacrificed #2 to get #1 and #3 ("brick-wall" front-end filters). Pick your poison.

[heavenfish]

fs/2 only works well if you want to reconstruct a sine wave. If you measure a 50 MHz square wave, 100 MS/s would reconstruct a sine wave on the screen. Of course whether it matters depends your applications. If you're dealing with digital signal and doing serial decoding, it still gives you all the information you need. If you cares about the shape not only timing then you probably want 500 MS/s.

[KE5FX]

It all depends on how good the reconstruction algorithm is. The thing is that according to Nyquist all information of the signal is there up to (but not including) fs/2. However if you LOOK at a sine wave which is close to fs/2 you'll only see a few seemingly random sample points. So in order to SEE the signal it has to be reconstructed and that is where reconstruction algorithms come into play. Still a higher than necessary samplerate doesn't add any extra information.

What some people may be overlooking is that the mathematics behind sampling describe how to reconstruct a continuous function.  An oscilloscope display isn't continuous, it's a stream of discrete, discontinuous frames displayed in time.  You can reconstruct what's on the screen accurately as long as Nyquist is satisfied, but that doesn't mean it will be particularly pleasant to look at a moving or changing signal near Nyquist, or even a repetitive one.



This is a 10 GS/s scope displaying a 3 GHz signal.  It's "correct" according to Nyquist, and no further information will be added by sampling at a higher rate, but you'd still prefer more oversampling margin if you could get it. 

[Wuerstchenhund]

What some people may be overlooking is that the mathematics behind sampling describe how to reconstruct a continuous function.  An oscilloscope display isn't continuous, it's a stream of discrete, discontinuous frames displayed in time.

Yes, but that does not matter. You can get a valid reconstruction even if you only had two sampling points.

You can reconstruct what's on the screen accurately as long as Nyquist is satisfied, but that doesn't mean it will be particularly pleasant to look at a moving or changing signal near Nyquist, or even a repetitive one.



This is a 10 GS/s scope displaying a 3 GHz signal.  It's "correct" according to Nyquist, and no further information will be added by sampling at a higher rate, but you'd still prefer more oversampling margin if you could get it. 

Yes, but that only looks so poor because you've enabled linear interpolation which never produces a true waveform. It's only there because it needs a lot less processing power so it will produce higher update rates on older/slower scopes and at very high oversampling rations the irregularities get so small that they can no longer be seen.

You should leave the scope on sin(x)/x which as we see produces a true waveform and which is the only interpolation function that produces true results as long as Nyquist-Shannon is satisfied.

[KE5FX]

Yes, but that only looks so poor because you've enabled linear interpolation which never produces a true waveform. It's only there because it needs a lot less processing power so it will produce higher update rates on older/slower scopes and at very high oversampling rations the irregularities get so small that they can no longer be seen.

You should leave the scope on sin(x)/x which as we see produces a true waveform and which is the only interpolation function that produces true results as long as Nyquist-Shannon is satisfied.

Point being, it looks shaky and twitchy even with sin(x)/x turned on.  I turned it off briefly to show how few points the scope has to work with. 

It would probably look quite a bit better if the firmware could map the trigger level back onto the sin(x)/x-interpolated waveform and adjust the horizontal position accordingly.  It doesn't look like they're attempting to do anything like that here, but I imagine more modern scopes can.  Of course, then you end up looking at trigger jitter...

[KE5FX]

With only two data points on a complete cycle of a waveform, you have no idea if it's a sine, or square or even a triangle, or maybe something else entirely.  Saying that "the 'scope can reconstruct an accurate rendition of the original signal with only two data points per full cycle" is not only naive, it's bordering on ridiculous.  Please stop, and THINK before you run on () about this...

If you only have two points per fundamental cycle to work with, you have no choice but to show a sine.  The signal has to be band-limited prior to sampling, with its content rolled off almost entirely before half the sample rate is reached.  From the point of view of the ADCs in the scope, it is a sine.

[testmode]

With only two data points on a complete cycle of a waveform, you have no idea if it's a sine, or square or even a triangle, or maybe something else entirely. 

I think this is the primary point of contention here.  "Reconstructing" a signal where one already has an idea of what to expect is entirely different than trying to "view" as much of an unknown signal as possible.  But of course one has to have some rough idea on the expected range of frequencies you have to care about else you'll just be throwing as many darts as you could with your eyes closed hoping somehow you'll hit the bull's eye.

[Wuerstchenhund]

With only two data points on a complete cycle of a waveform, you have no idea if it's a sine, or square or even a triangle, or maybe something else entirely.  Saying that "the 'scope can reconstruct an accurate rendition of the original signal with only two data points per full cycle" is not only naive, it's bordering on ridiculous.  Please stop, and THINK before you run on () about this...

You really can't make that up...

Maybe you should take your own advice and next time read & think twice before writing silly nonsense. Because for a start I said *nothing* about a complete cycle (which would be silly, as Nyquist-Shannon states that the sample rate needs to be higher than 2x f₀, so 2 points per period are clearly not sufficient to get a true reconstruction of a true sine wave)

That however doesn't change the fact that with a BW-limited signal, sampled at >2xf₀, two sample points are sufficient to truly reconstruct the segment between these two points with sin(x)/x interpolation.

It also doesn't matter what waveform it is, as long as it's BW limited (i.e. the highest frequency components are sampled at a rate that satisfies Nyquist-Shannon).

Point being, it looks shaky and twitchy even with sin(x)/x turned on.  I turned it off briefly to show how few points the scope has to work with.

It looks shaky and twitchy very likely because of irregularities in the signal (i.e. phase noise, quantization noise), which means you don't get a true sine but something else.

What's your signal source?

[EEVblog]

That however doesn't change the fact that with a BW-limited signal, sampled at >2xf₀, two sample points are sufficient to truly reconstruct the segment between these two points with sin(x)/x interpolation.

For a gaussian response scope front end you should be using at least 4xf sample rate is the typical figure quoted.
A minimum of 2.5xf if you have a sharp flat response front end.
http://cp.literature.agilent.com/litweb/pdf/5988-8008EN.pdf

[nctnico]

With only two data points on a complete cycle of a waveform, you have no idea if it's a sine, or square or even a triangle, or maybe something else entirely.  Saying that "the 'scope can reconstruct an accurate rendition of the original signal with only two data points per full cycle" is not only naive, it's bordering on ridiculous.  Please stop, and THINK before you run on () about this...

I'd strongly suggest to read up about Fourier and sampling theory before typing more nonsense. When people use an oscilloscope they expect it to show the actual signal at the tip of the probe. Unfortunately it never works that way. An oscilloscope and the probe will always have limits and you have to be aware of those limits. When you look at a 50MHz square wave with any oscilloscope which has a 100MHz bandwidth you'll see a sine wave. There just isn't enough bandwidth to show the higher harmonics.

I have done quite a bit of research on signal reconstruction algorithms and managed to come up with one which can reconstruct up to 0.45fs (while including the original samples) so I do know what I'm talking about and what is/isn't possible.

[nctnico]

It all depends on how good the reconstruction algorithm is. The thing is that according to Nyquist all information of the signal is there up to (but not including) fs/2. However if you LOOK at a sine wave which is close to fs/2 you'll only see a few seemingly random sample points. So in order to SEE the signal it has to be reconstructed and that is where reconstruction algorithms come into play. Still a higher than necessary samplerate doesn't add any extra information.

What some people may be overlooking is that the mathematics behind sampling describe how to reconstruct a continuous function.  An oscilloscope display isn't continuous, it's a stream of discrete, discontinuous frames displayed in time.  You can reconstruct what's on the screen accurately as long as Nyquist is satisfied, but that doesn't mean it will be particularly pleasant to look at a moving or changing signal near Nyquist, or even a repetitive one.

This is a 10 GS/s scope displaying a 3 GHz signal.  It's "correct" according to Nyquist, and no further information will be added by sampling at a higher rate, but you'd still prefer more oversampling margin if you could get it.

Again: there is a difference between sampling enough points to reconstruct the signal (with a DAC for example) and getting enough points to SEE a signal. However getting enough points to SEE a signal is a matter of using a signal reconstruction algorithm. You don't need a higher samplerate for that because all the information needed for the signal reconstruction algorithm to work is there. Our brains are the problem here, not the scope or the sampling frequency!

[omgfire]

And to elaborate, while Nyquist theorem is all about 1's and 0's, it is in fact about the digital representation of the underlying analog signal.

Last time I checked Nyquist–Shannon–Kotelnikov sampling theorem, it was defined in the field of real numbers (possibly infinite length decimal representation). How do you digitally represent real (specifically irrational) numbers? Scopes work with quantized samples (8 bit ADC, 16 bit ADC, ..). It is possible to mathematically analyze how quantization butchers signal: http://uwspace.uwaterloo.ca/bitstream/10012/3867/1/thesis.pdf
But Nyquist–Shannon–Kotelnikov sampling theorem do not touch quantization and I am not sure where you find "all about 1's and 0's" in this theorem.

[omgfire]

fs/2 only works well if you want to reconstruct a sine wave.

Yes, but scopes frontend bandwidth is also specified for sine wave and signal can be decomposed into Fourier series.

If you measure a 50 MHz square wave, 100 MS/s would reconstruct a sine wave on the screen. If you cares about the shape not only timing then you probably want 500 MS/s.

50 MHz square wave is NOT bandwidth limited to 50 MHz. 70 MHz limited frontend will filter 50 MHz square wave into sine wave, after that you can sample it at 500 MS/s or 5 GS/s, but it still would be sine wave.

To see fifth harmonic you would need over 250 MHz of bandwidth and consequently over 500 MS/s. But sample rate of 500 MS/s alone would not help to see 50 MHz square wave on 70 MHz bandwidth limited scope.

[omgfire]

With only two data points on a complete cycle of a waveform, you have no idea if it's a sine, or square or even a triangle, or maybe something else entirely.  Saying that "the 'scope can reconstruct an accurate rendition of the original signal with only two data points per full cycle" is not only naive, it's bordering on ridiculous.  Please stop, and THINK before you run on () about this...

indeed.

If signal is bandwidth limited to X MHz, I am pretty sure signal is NOT X MHz square wave or X MHz triangle wave. Because X MHz square wave is not bandwidth limited to X MHz.

[Wuerstchenhund]

Last time I checked Nyquist–Shannon–Kotelnikov

Don't forget Whittaker

sampling theorem, it was defined in the field of real numbers (possibly infinite decimal). How do you digitally represent infinite decimal? Scopes work with quantized samples (8 bit ADC, 16 bit ADC, ..).

Indeed, which is why even if you'd manage to feed a pure, perfect sine wave to a scope with sufficient bandwidth and an excessive sample rate, the acquired waveform would still not be a perfect sine wave but a (very close) approximation.

It is possible to mathematically analyze how quantization butchers signal: http://uwspace.uwaterloo.ca/bitstream/10012/3867/1/thesis.pdf
But Nyquist–Shannon–Kotelnikov sampling theorem do not touch quantization and I am not sure where you find "all about 1's and 0's" in this theorem.

You won't, because as you stated the theorem is a mathematical product in the real domain, actually considering analog sampling.

As to quantization errors, the only way out is increased (true) vertical resolution, which won't eliminate the errors (which are inherent in ADCs) but at least minimize them.

[nctnico]

If you are going to argue about quantization errors then you'd also need to include the number of pixels on the screen! At some point all of this is pretty moot because the frequency response of a scope isn't prefect, the analogue input stage will have some distortion, noise (ofcourse), frequency dependant phase shift and there are probably some other factors I didn't mention.

edit: typo

[testmode]

And to elaborate, while Nyquist theorem is all about 1's and 0's, it is in fact about the digital representation of the underlying analog signal.

Last time I checked Nyquist–Shannon–Kotelnikov sampling theorem, it was defined in the field of real numbers (possibly infinite length decimal representation). ...
...
...
... But Nyquist–Shannon–Kotelnikov sampling theorem do not touch quantization and I am not sure where you find "all about 1's and 0's" in this theorem.

The 1's and 0's are in the context of our discussion. Although technically your argument is correct, we don't need to go into such level of depth of that subject here I suppose.  It is already a given that we are discussing the theorem in the context of how it applies to quantization.

[lukier]

If you have a digital camera, more pixels is better-- especially if you want to zoom in on a particular section of the photo to see more detail.  Everyone that has actually done this has noticed that the photos becomes "pixelated" as you continue to zoom in. 

Nope. Like in the oscilloscopes, the full optical path matters. In the digital camera case the lens itself will be the limiting factor due to the Airy Disk and the manufacturing quality. More on that here:
http://www.edmundoptics.co.uk/resources/application-notes/imaging/limitations-on-resolution-and-contrast-the-airy-disk/

That's why there are so called "megapixel" lenses in machine vision and more expensive too. So many MPix camera with a crappy piece of plastic for the lens will not give you any more detail if you zoom in. It won't be pixelated, it will be just blurred over many pixels, all containing redundant data (no extra information) - just a waste of sensor's silicon, ADC power consumption and data bus bandwith to transmit them. Instead a sensor with less pixels, but bigger to fit the Airy Disk would be better for different reasons (bigger pixels are more light sensitive and less noisy). In the analogy, think of the lens as probe + front end, and instead of a bigger sensor (faster GPSPS ADC) the smaller sensor with bigger pixels = slower ADC but with 16 bits for example.

I understand your point that when debugging extra bandwith and sampling might be helpful, because it might turn out the signal is a square wave (so much higher harmonics) etc. However, here we discuss  the specs, and these are specified for a pure sine and here the full signal path will dampen the signal long before it reaches ADC (probe, front end with roll off etc). Therefore (esp. with sinx/x) ADC will not reconstruct the sine wave much better than with just Nyquist. If the result with sinx/x and 2 samples is identical to the shape from 10x oversampled waveform then this oversampling didn't bring anything to the table (and it won't because any deviation from pure sine, noise spike for example, in these 10x samples would mean there is higher frequency component there and that would be gone in the probe and the front end).

[KE5FX]

It looks shaky and twitchy very likely because of irregularities in the signal (i.e. phase noise, quantization noise), which means you don't get a true sine but something else.

Nope, the signal is rock-stable, coming from an HP 8672A synthesizer.  It would take a helluva lot of phase noise to look like that.

Most of the apparent jitter is simply due to the inability of the scope to place the trigger point consistently from one acquisition to the next.  It would have looked better if the triggering system operated on the final reconstructed waveform, but that has some pretty severe drawbacks of its own (as I'm sure you're aware.)  A hybrid approach would be best.  I'm not sure if the TDS 694C was the first 10 GS/s realtime scope, but it was one of the first, and there are a few rough edges.

[nctnico]

It looks shaky and twitchy very likely because of irregularities in the signal (i.e. phase noise, quantization noise), which means you don't get a true sine but something else.

Nope, the signal is rock-stable, coming from an HP 8672A synthesizer.  It would take a helluva lot of phase noise to look like that.

Most of the apparent jitter is simply due to the inability of the scope to place the trigger point consistently from one acquisition to the next.  It would have looked better if the triggering system operated on the final reconstructed waveform, but that has some pretty severe drawbacks of its own (as I'm sure you're aware.)

It seems you (or the person who made the video) are feeding TDS694C a 3.1GHz sine wave. IMHO it should be able to trigger on it but it may take some fiddling with the trigger level to get it stable.

[KE5FX]

It looks shaky and twitchy very likely because of irregularities in the signal (i.e. phase noise, quantization noise), which means you don't get a true sine but something else.

Nope, the signal is rock-stable, coming from an HP 8672A synthesizer.  It would take a helluva lot of phase noise to look like that.

Most of the apparent jitter is simply due to the inability of the scope to place the trigger point consistently from one acquisition to the next.  It would have looked better if the triggering system operated on the final reconstructed waveform, but that has some pretty severe drawbacks of its own (as I'm sure you're aware.)

It seems you (or the person who made the video) are feeding TDS694C a 3.1GHz sine wave. IMHO it should be able to trigger on it but it may take some fiddling with the trigger level to get it stable.

It's at 3 GHz exactly, which is the spec limit. 

The trigger subsystem in these scopes works really well assuming you don't have a bad ASIC, about which plenty has been written elsewhere.  It can trigger on a 3 GHz signal at -30 dBm or lower.  But the triggering process runs independently of waveform acquisition, so when a trigger comes in, it could be anywhere between two of the three available sample points per cycle.  That ambiguity manifests itself as visible jitter.

If the scope were able to capture several points per cycle instead of just three, the asynchronous nature of the trigger and acquisition systems would be proportionally less noticeable.  The 694C is great for single-shot acquisition, but repetitive sweeps will never really look stable at higher frequencies. 

It would be interesting to feed a 6 GHz signal to a 20 GS/s DSO6000X-series scope -- to bring the thread back on-topic -- to see how stable it looks in comparison.  I'm guessing they reposition the reconstructed waveform slightly at each sweep to place the trigger point at its proper spot.

[nctnico]

It looks shaky and twitchy very likely because of irregularities in the signal (i.e. phase noise, quantization noise), which means you don't get a true sine but something else.

Nope, the signal is rock-stable, coming from an HP 8672A synthesizer.  It would take a helluva lot of phase noise to look like that.

Most of the apparent jitter is simply due to the inability of the scope to place the trigger point consistently from one acquisition to the next.  It would have looked better if the triggering system operated on the final reconstructed waveform, but that has some pretty severe drawbacks of its own (as I'm sure you're aware.)

It seems you (or the person who made the video) are feeding TDS694C a 3.1GHz sine wave. IMHO it should be able to trigger on it but it may take some fiddling with the trigger level to get it stable.

It's at 3 GHz exactly, which is the spec limit. 

The trigger subsystem in these scopes works really well assuming you don't have a bad ASIC, about which plenty has been written elsewhere.  It can trigger on a 3 GHz signal at -30 dBm or lower.  But the triggering process runs independently of waveform acquisition, so when a trigger comes in, it could be anywhere between two of the three available sample points per cycle.  That ambiguity manifests itself as visible jitter.

The triggering in a DSO doesn't work that way in general; they all have circuitry (a trigger time interpolator) to align subsequent acquisitions precisely on top of eachother. Otherwise triggering on high frequency signals would not work at all (especially in equavalent time sampling mode) and cause the jittery picture in the video.
From what I know specifically from the Tektronix TDS500 and TDS700 series is that they have a trigger time interpolator which measures the trigger point versus the sampling clock in order to put the trace at the right point on the screen. This leaves two possible causes for the effect shown in the video: the trigger level isn't adjusted properly or the scope is broken.

[KE5FX]

This leaves two possible causes for the effect shown in the video: the trigger level isn't adjusted properly or the scope is broken.

That's what I'm saying -- I'd expect this feature in newer scopes, but it's not universal by any means. 

Why, in your opinion, would anyone bother using a 20 GS/s sampler in a 6 GHz scope, if perfect, stable reconstruction is possible at 0.4 fs or even higher?

[nctnico]

This leaves two possible causes for the effect shown in the video: the trigger level isn't adjusted properly or the scope is broken.

That's what I'm saying -- I'd expect this feature in newer scopes, but it's not universal by any means. 

Why, in your opinion, would anyone bother using a 20 GS/s sampler in a 6 GHz scope, if perfect, stable reconstruction is possible at 0.4 fs or even higher?

I think jjoonathan summed it up nicely in an earlier post:

1. Full fs/2 bandwidth
2. Good step response
3. Good out-of-band signal rejection

Modern oscilloscopes sacrifice #1 to get #2 and #3. Last generation sacrificed #2 to get #1 and #3 ("brick-wall" front-end filters). Pick your poison.

[Wuerstchenhund]

It would be interesting to feed a 6 GHz signal to a 20 GS/s DSO6000X-series scope -- to bring the thread back on-topic -- to see how stable it looks in comparison.  I'm guessing they reposition the reconstructed waveform slightly at each sweep to place the trigger point at its proper spot.

I can't offer a 6Ghz signal on a 6GHz scope as I don't have the necessary equipment at home but if I find the time this evening anytime soon I'll get some video of a 3Ghz sine wave on a slightly more modern 20GSa/s scope (I got a new video gizmo to capture VGA output so that's a good opportunity to try it )

Why, in your opinion, would anyone bother using a 20 GS/s sampler in a 6 GHz scope, if perfect, stable reconstruction is possible at 0.4 fs or even higher?

I think jjoonathan summed it up nicely in an earlier post:

1. Full fs/2 bandwidth
2. Good step response
3. Good out-of-band signal rejection

Modern oscilloscopes sacrifice #1 to get #2 and #3. Last generation sacrificed #2 to get #1 and #3 ("brick-wall" front-end filters). Pick your poison.

This.

Also, Scope manufacturers develop their ADCs in certain steps (like 1-2-5-10-20-40-80-160-240 GSa/s), and for a 6GHz signal Nyquist-Shannon wants a sampling rate larger than 12GSa/s (plus some more for filter roll-off atc), so 20GSa/s isn't such a far off choice and using an existing ADC is cheaper than developing say a 15GSa/s just for that one scope.

Also, many scope series are offered with different BW ranges (some of them even BW upgradeable), and usually they come with the same acquisition system for all models as its cheaper than to give each BW step its own acquisition system variant with varying sample rates (which would also complicate BW upgrades).

[siggi]

It would probably look quite a bit better if the firmware could map the trigger level back onto the sin(x)/x-interpolated waveform and adjust the horizontal position accordingly.  It doesn't look like they're attempting to do anything like that here, but I imagine more modern scopes can.  Of course, then you end up looking at trigger jitter...

I know the 5/700-series TDS scopes have interpolators to measure the time from trigger to a sample clock edge, so they effectively do this in hardware. I've never seen schematics for a 600-series TDS scope, so I don't know whether they attempt the same thing, but your triggering looks pretty loosey-goosey for sure .

[Wuerstchenhund]

Again, more bullshit from the math professors.

   Look, it's pretty clear now that you don't understand basic signal processing, but that's no reason to become aggressive.

ALL digital sampling systems only provide you with a presentation of the data that is an approximation of the actual signal.  The more data points you have in a given time period, the better that approximation will be.  I don't understand why people don't get this.

*Any* scope only provides you with an approximation of the actual signal, even the analog scopes which is probably with what you spent most of your 40 years "experience" on.

The key is to know how a specific instrument impacts the measurement.

If you have a digital camera, more pixels is better

  No, it's not. As others explained more pixels are useless if the optical path limits the physical resolution. There are tons of high MPx cameras out there who take shit pictures because they only have a crappy plastic lens.

When I use a 'scope to look at a signal in the real world (as opposed to the dreamy Utopian academic world), I'm needing to look at the signal because there might be something there that I'm not expecting.  If the signal does not look like it's supposed to, then I need to take action to correct the problem, which might be any number of things.  Mathematical reconstruction algorithms (and I have used them too) only work well when you know in advance what the signal is supposed to look like.  When we are debugging a design, we don't know in advance what the signal will look like, especially if the circuit is misbehaving.  So, in this case, it's not a matter of applying a mathematical model to reconstruct the signal from a limited data set.  It's a matter of having an overwhelming amount of sample points such that reconstruction of the signal is not necessary other than perhaps a small amount of sin(x)/x smoothing for "nice looking" interpolation between data points.  More samples per horizontal division equals a better idea of what's really going on at the probe tip.

No, it doesn't.   

Besides, signal theory isn't just an abstract thing, it's how the real world works, and basic knowledge for every engineer who works with any kind of signal processing. Fending it off as "bullshit" is stupid and only highlights your ignorance.

So, you are not impressing me with your academic view of a real-world problem, especially when empirically derived data does not match with your theoretical nonsense.  And worse yet, you are fooling younger players into believing that their 500MHz 'scope will be able to see a 500MHz signal with astounding detail.

Frankly, the real world gives a shit if you're impressed or not, facts and realities are not going away just because you put fingers in your ear to avoid getting confronted with it.

I have to say it's actually quite shocking to see someone who claims to be an engineer being so hostile to what really is basic knowledge for any EE these days. To some extend I understand that this isn't necessarily something that was taught 40 years ago, but a good engineer doesn't stop stop learning after graduation.

You'd be well advised to heed some of the advice that was given, and get a better understanding with the basic principles that make DSOs work. Your understanding of what you're measuring will improve as well. A lot.

I don't know....  Kids these days ...

Yeah, stupid kids.  All young and dumb, right?  

FYI, many of the posters here are a lot closer to retirement than graduation, and that includes me. Which shows you don't have to be young to understand signal processing. 

[G0HZU]

The issue here is that you are both looking at this from different angles. Whilst it's useful to have a basic grasp of sampling theory you do also have to consider the real world. This means real world signals and the limitations of real world instruments.

Hiding behind sampling theory with a perfect sinewave test signal only gets you so far. I think DM is trying to tell you that you usually won't 'know' the spectrum of signals that are arriving at the scope input.

So you can get issues when your scope doesn't have enough sample rate to cope with the full spectrum of signals that can get through to the sampler. So you can see strange effects.

The scope sampling process itself won't be perfect in various ways and this can cause fake artifacts to appear too. So even a high sample rate isn't enough on its own if the scope hardware is flawed. All of this can mean that interpolation/reconstruction algorithms can let you down in the real world with real world signals and real world scopes.

You can quote sampling theory with your perfect sinewave until you are blue in the face but that won't change the fact that some DSOs can suffer sampling problems, eg alias effects due to their inadequate (max) sample rate wrt the spectrum of signals that can actually get through to the sampler. eg there are going to be scopes marketed as a 500MHz BW model with 2GS/s that are going to have subtle alias issues despite the 4x ratio of the 500MHz BW logo and 2GS/s sample rate. Other scopes may have subtle issues with the sample timing within the ADC hardware. The result of this will be a reconstruction algorithm that gives false artifacts on the display.

i.e. telling DM (again and again) that a perfect sinewave can in theory be reconstructed with a certain sample rate doesn't solve the problems that real scopes face with real signals.

[nctnico]

You make it sound like black magic again. However it is the other way around: if you have a good grasp of sampling theory you know the limitations of the DSO you are using and thus can  identify artifacts and aliasing issues more quickly even if you don't know the spectrum of a signal. Peak-detect is one of the tools on a DSO which is very helpfull with that.

You also have to realise that a sine wave must have a significant amount of distortion before it starts looking odd on an oscilloscope. So even though the hardware and the signal reconstruction algorithm may not be perfect chances are these do not result in visual distortions.

[lem_ix]

This is engineering, you don't just put a better adc because you *feel* you need it, same with the analog front end. Bottom line a 500 mhz scope only means that you'll be able to see a 500 mhz spectral component reasonably well. For starters maybe use FFT on a square wave and see what you're dealing with. For example you need a 100 Thz scope  to see why this discussion is going on under this topic Maybe it's a good topic for the next vid in Dave's scope series.

[G0HZU]

I'm not trying to make it sound like black magic. I'm just trying to say that real world signals are not just pure sinewaves and real world hardware doesn't always sample accurately (or fast enough) to prevent artifacts appearing on the display.

Also, I think you will agree that you can't just rely on the real time sampling mode when looking at wideband signals that cause aliasing. The repetitive mode on my old HP 2GS/s DSO can be useful here. But if I just looked at 500MHz 2GS/s on the front panel I might think that I can look at any waveform in real time mode with no risk of aliasing artefacts. But this isn't the case in reality.

You also have to realise that a sine wave must have a significant amount of distortion before it starts looking odd on an oscilloscope. So even though the hardware and the signal reconstruction algorithm may not be perfect chances are these do not result in visual distortions.

Someone with more scope experience than me may be best placed to answer this but try using a scope that uses lots of (interleaved) ADCs that have to be carefully synched up in order to prevent sampling artefacts becoming too objectionable. If there is imbalance in the scaling or timing then you can begin to see distortion on a sinewave in the scope hardware caused by reconstruction anomalies.

Going back a few posts, I could post up what my old HP54540C looks like with a 600MHz cw signal from a sig gen and it's going to look fairly similar to what KE5FX produced on that old Tek TDS694C scope in terms of wobble/jitter. But the reason I didn't comment on the scope video (until now) was because I can't trust what a youtube video is going to show me because I don't know what is caused by the scope and what is caused by the camera and/or youtube from frame to frame. Obviously, there is some wobble/jitter but I'd prefer to look at this directly rather than via a camera and youtube.

But with my admittedly limited experience of using fast DSOs I'd expect to see wobble on the signal when sampling a 3GHz signal at 10GS/s using interpolation on a real world scope like that old Tek TDS694C. But I haven't tried to make too much sense of the youtube video because of the risks of compression artefacts in the video. Also, I've never used a Tek TDS694C.

[nctnico]

When using interleaved ADCs the calibration procedure cancels all the errors so together with a stable design it will produce good repeatable results. Otherwise the DSO would be useless and the whole exersize to build it futile.

[nfmax]

The wobble/jitter on the video under discussion may simply be due to less than perfect reconstruction. In general, the signal displayed is not synchronous with the ADC clock. If the trigger is operating correctly, x position on the screen is a function purely of the time from the trigger point. On each successive acquisition, the ADC sample clocks will be at different offsets from the trigger instant because the ADC clock is not synchronous with the displayed signal. Hence on successive sweeps the 'dots' will move, wobble, or jitter with respect to the graticule. This is the correct behaviour. If you select linear interpolation, the straight lines joining these wobbling dots will jump around all over the place, when the signal displayed occupies a large fraction of the Nyquist bandwidth. If you switch to perfect sinx/x interpolation (and the trigger is operating correctly), you should end up with a smooth, stable signal, on which the sample dots (if shown) jump around from acquisition to acquisition, but without changing the shape of the interpolated curve..

This effect is clearly evident when linear interpolation is used: it reduces dramatically, but does not vanish entirely, when sinx/x interpolation is used. This may be because the approximation to sinx/x used by the scope is not very accurate (it has to be an approximation as true sinx/x requires an infinitely long time record); or because a digital trigger interpolator in the scope is using linear interpolation instead of of sinx/x; or because an analog trigger interpolator can select among only a discrete number of interpolation delays. Tektronix invented triggered sweep: I don't think the trigger will be to blame (unless there is an instrument fault, of course). My suspicion is a poor choice of window, or too short a window, on the sinx/x interpolator, probably a limitation of the technology at the time.

[G0HZU]

When using interleaved ADCs the calibration procedure cancels all the errors so together with a stable design it will produce good repeatable results. Otherwise the DSO would be useless and the whole exersize to build it futile.

So people who try and evaluate the effects of interleave distortion in scopes and write papers about it are just wasting their time because this form of distortion doesn't exist in real scopes because you can just calibrate it away?

It's also interesting that in your world the scope hardware is either error free or it is useless.

[G0HZU]

This is engineering, you don't just put a better adc because you *feel* you need it, same with the analog front end. Bottom line a 500 mhz scope only means that you'll be able to see a 500 mhz spectral component reasonably well. For starters maybe use FFT on a square wave and see what you're dealing with. For example you need a 100 Thz scope  to see why this discussion is going on under this topic Maybe it's a good topic for the next vid in Dave's scope series.

Yes, I can give an extreme example here. My HP54540C has an AC test signal that is a 500Hz square wave (yes, just 500 Hertz) but the scope can't evaluate this waveform properly even at 1GS/s in real time mode.  It looks better at 2GS/s in real time but even then I can see some subtle alias effects on the signal. It does much better in repetitive mode. I think the scope would work slightly better if it could manage 4GS/s in real time but the benefits would only be small. It therefore depends on how critical the requirements are and how forgiving the user is with respect to playing with the scope to provide a workaround. eg the user can switch to repetitive mode if this mode is suitable to use on the waveform under test and they can then get a much higher effective sample rate.

[nctnico]

When using interleaved ADCs the calibration procedure cancels all the errors so together with a stable design it will produce good repeatable results. Otherwise the DSO would be useless and the whole exersize to build it futile.

So people who try and evaluate the effects of interleave distortion in scopes and write papers about it are just wasting their time because this form of distortion doesn't exist in real scopes because you can just calibrate it away?

It's also interesting that in your world the scope hardware is either error free or it is useless.

You are reading something which isn't there. If you don't calibrate the errors away then you'll see them for sure and the waveform gets distorted. Look at the thread about hacking the TDS744A into a TDS784A by changing an option jumper. Because the ADCs are used for interleaving at 4Gs/s instead of 2Gs/s a new calibration / adjustment procedure is needed.

[G0HZU]

The wobble/jitter on the video under discussion may simply be due to less than perfect reconstruction. In general, the signal displayed is not synchronous with the ADC clock. If the trigger is operating correctly, x position on the screen is a function purely of the time from the trigger point. On each successive acquisition, the ADC sample clocks will be at different offsets from the trigger instant because the ADC clock is not synchronous with the displayed signal. Hence on successive sweeps the 'dots' will move, wobble, or jitter with respect to the graticule. This is the correct behaviour. If you select linear interpolation, the straight lines joining these wobbling dots will jump around all over the place, when the signal displayed occupies a large fraction of the Nyquist bandwidth. If you switch to perfect sinx/x interpolation (and the trigger is operating correctly), you should end up with a smooth, stable signal, on which the sample dots (if shown) jump around from acquisition to acquisition, but without changing the shape of the interpolated curve..

This effect is clearly evident when linear interpolation is used: it reduces dramatically, but does not vanish entirely, when sinx/x interpolation is used. This may be because the approximation to sinx/x used by the scope is not very accurate (it has to be an approximation as true sinx/x requires an infinitely long time record); or because a digital trigger interpolator in the scope is using linear interpolation instead of of sinx/x; or because an analog trigger interpolator can select among only a discrete number of interpolation delays. Tektronix invented triggered sweep: I don't think the trigger will be to blame (unless there is an instrument fault, of course). My suspicion is a poor choice of window, or too short a window, on the sinx/x interpolator, probably a limitation of the technology at the time.

Yes, it's difficult to guess what is happening in the video. If I had access to the TDS694C then I'd try a few experiments. I'd make sure that the 3GHz test signal had very low harmonic distortion (add a lowpass filter?) and then feed it to the scope. This would rule out distortion issues with the signal itself.

Presumably the trigger issue could be ruled out if the scope was set to single shot mode. Just take one trace and then do an FFT on the data? If the scope can't do this then maybe dump out the raw data to Excel or Matlab and do an FFT offline.

I'm not a scope guru but my guess is that the FFT may well show what is happening. If the problem is noise related then the FFT would show just noise and the 3GHz signal and low distortion terms.

However, if this was a noise/interpolation/distortion? issue then I think the scope FFT may well show folded back harmonic terms in the display. So the FFT may show the 3GHz signal but also folded back harmonic distortion terms that appear as alias terms at 1GHz, 2GHz, 4GHz etc. These would cause wobble on the signal when viewed when the scope was set back to 'run' mode such that several traces per second are displayed. If the display was a lot faster in terms of displayed waveforms per second, you would probably just see a fatter/graded trace that would smear the wobble making it appear less obvious. But all this is just a guess, I don't do much with digital scopes I'm really just an RF person.

[nctnico]

This guy doesn't seem to have problems triggering on a 3GHz signal but I just browsed through the video quickly since it is way past bedtime for me:

[KE5FX]

Yes, it's difficult to guess what is happening in the video. If I had access to the TDS694C then I'd try a few experiments. I'd make sure that the 3GHz test signal had very low harmonic distortion (add a lowpass filter?) and then feed it to the scope. This would rule out distortion issues with the signal itself.

As I pointed out earlier, the 3 GHz test signal is fine.  No harmonic problems, and it has about 140 fs of jitter in the 1 Hz-100 Hz range that would affect display stability.



It's tough to support a claim that "they all do that" based on N=2, but I have two TDS694Cs and they behave exactly the same.  (Edit: N=3, looking at the video in nctnico's post near 6:20.)  The only way that acquisition could look rock-solid from one sweep to the next is if either (a) the sampling rate were much higher -- perhaps 30 GHz or more -- or (b) the scope were capable of interpolating the trigger point to a position relative to the reconstructed sine wave.

The TDS694C's claim to fame was its realtime nature.  There were plenty of sampling scopes capable of doing a better job rendering a 3 GHz CW signal, but the 694C was meant for single-shot acquisitions, which in 1999 was comparatively rare in the 3 GHz class.   It's like watching a pig fly -- it would not normally occur to me to criticize its form, because I'm impressed that the thing got off the ground in the first place.   I'm sure LeCroy had something on the market that would blow the 694C away, of course, but it would have been relatively obscure and I probably haven't heard of it. 

Presumably the trigger issue could be ruled out if the scope was set to single shot mode. Just take one trace and then do an FFT on the data? If the scope can't do this then maybe dump out the raw data to Excel or Matlab and do an FFT offline.

I'm not a scope guru but my guess is that the FFT may well show what is happening. If the problem is noise related then the FFT would show just noise and the 3GHz signal and low distortion terms.  However, if this was a noise+interpolation issue then I think the scope FFT may well show folded back harmonic terms in the display caused by the less than perfect interpolation. So the FFT may show the 3GHz signal but also folded back harmonic distortion terms that appear as alias terms at 1GHz, 2GHz and 4GHz caused by the imperfect interpolation and limited sample rate. These would cause wobble on the signal when viewed when the scope was set back to 'run' mode such that several traces per second are displayed. If the display was a lot faster in terms of displayed waveforms per second, you would probably just see a fatter/graded trace that would smear the wobble making it appear less obvious. But all this is just a guess.

Several different things could be happening.  Timebase jitter could do it (although it would have to be really severe), low-quality interpolation certainly wouldn't help, a missing (or possibly faulty) trigger interpolator could be responsible, inadequate antialias filtering could do it if the HP 8672A had significant harmonic content (which it doesn't), but IMHO the only real problem is a low oversampling margin in a scope that's too old to hide its faults in software.   

If I look at the FFT display, there's about 15 dB of suppression on the alias at 7 GHz:



However, that "15 dB" is an artifact of performing the FFT in screenspace, like a lot of older scopes do.   We're just seeing the Fourier transform of some connected dots on a screen.   That places Tektronix in a state of sin(c):



Again, the fact that this scope is almost 20 years old gives them some room for absolution, I think. 

[MarkL]

...
Several different things could be happening.  Timebase jitter could do it (although it would have to be really severe), low-quality interpolation certainly wouldn't help, a missing (or possibly faulty) trigger interpolator could be responsible, inadequate antialias filtering could do it if the HP 8672A had significant harmonic content (which it doesn't), but IMHO the only real problem is a low oversampling margin in a scope that's too old to hide its faults in software.   
...

I think G0HZU's idea to examine the FFT is a good approach, but it has to be done with more points and no interpolation getting in the way.

Do you want to do a max points binary capture and post it?  I wouldn't mind playing around with it.  Could be interesting.

[KE5FX]

...
Several different things could be happening.  Timebase jitter could do it (although it would have to be really severe), low-quality interpolation certainly wouldn't help, a missing (or possibly faulty) trigger interpolator could be responsible, inadequate antialias filtering could do it if the HP 8672A had significant harmonic content (which it doesn't), but IMHO the only real problem is a low oversampling margin in a scope that's too old to hide its faults in software.   
...

I think G0HZU's idea to examine the FFT is a good approach, but it has to be done with more points and no interpolation getting in the way.

Do you want to do a max points binary capture and post it?  I wouldn't mind playing around with it.  Could be interesting.

There's only so much it could tell us, unfortunately.  Being generated from a real signal, it would have no useful data past Nyquist (5 GHz in this case.)   And at 130K points, it would be much too short to reveal the close-in noise pedestal of the sampling clock.

I did try feeding in 7 GHz to see how good the analog antialiasing filter was.  I don't remember the exact figure but it was at least 30-40 dB down.  Sure wish somebody would leak the schematics for this scope...

[MarkL]

There's only so much it could tell us, unfortunately.  Being generated from a real signal, it would have no useful data past Nyquist (5 GHz in this case.)   And at 130K points, it would be much too short to reveal the close-in noise pedestal of the sampling clock.

I did try feeding in 7 GHz to see how good the analog antialiasing filter was.  I don't remember the exact figure but it was at least 30-40 dB down.  Sure wish somebody would leak the schematics for this scope...

I was also going to try running a sin(x)/x reconstruction on it to see if there was the amplitude variation evident in the video.  I agree there's probably nothing to be seen with only 130k pts unless there's something terribly wrong (I thought the record length was longer).

[EEVblog]

So after 5 pages of this did anyone figure out if Keysight are releasing a new 2000/3000 scope in the next few months?

[MarkL]

So after 5 pages of this did anyone figure out if Keysight are releasing a new 2000/3000 scope in the next few months?

I'm sure the answer will become clear after we figure out why Tektronix's sin(x)/x doesn't work well.

[nctnico]

So after 5 pages of this did anyone figure out if Keysight are releasing a new 2000/3000 scope in the next few months?

I don't think anyone cares. Stay tuned...

[JPortici]

pretty sure daniel answered the question in first or second page

[Hydrawerk]

So after 5 pages of this did anyone figure out if Keysight are releasing a new 2000/3000 scope in the next few months?

Well, there is still no industrial competitor for these Keysight scopes from Tektronix or LeCroy.
OK, someone might like WaveSurfer 3000 or Tek MSO2000B.
Keysight has no need to hurry with a new scope model.

[G0HZU]

...
Several different things could be happening.  Timebase jitter could do it (although it would have to be really severe), low-quality interpolation certainly wouldn't help, a missing (or possibly faulty) trigger interpolator could be responsible, inadequate antialias filtering could do it if the HP 8672A had significant harmonic content (which it doesn't), but IMHO the only real problem is a low oversampling margin in a scope that's too old to hide its faults in software.   
...

I think G0HZU's idea to examine the FFT is a good approach, but it has to be done with more points and no interpolation getting in the way.

Do you want to do a max points binary capture and post it?  I wouldn't mind playing around with it.  Could be interesting.

There's only so much it could tell us, unfortunately.  Being generated from a real signal, it would have no useful data past Nyquist (5 GHz in this case.)   And at 130K points, it would be much too short to reveal the close-in noise pedestal of the sampling clock.

I did try feeding in 7 GHz to see how good the analog antialiasing filter was.  I don't remember the exact figure but it was at least 30-40 dB down.  Sure wish somebody would leak the schematics for this scope...

I was really thinking more in terms of the total wideband system noise. I'm sure your sig gen will not be this noisy (unless it was faulty) but a 3GHz BW is 95dBHz so a wideband noise floor of -135dBc/Hz would produce a S/N ratio of about 40dB in this BW. Presumably, this level of noise would be just enough to begin to show on the scope trace.

Also, I don't know much about the wideband noise contribution in the scope itself. This could come from various places and some of it may even fold over to make things worse. But I'm just guessing.

That was the idea of the FFT analysis. Dump out a full single shot and see if it shows lots of noise or if there are discrete distortion terms visible caused by sampling effects etc.

It might help with the diagnosis.

[LabSpokane]

So after 5 pages of this did anyone figure out if Keysight are releasing a new 2000/3000 scope in the next few months?

Yes.  I have the only one.  It has a 3dB brick wall bandwidth of 867.5309 GHz +/- 6.022x10^-23 Hz.

The front end is so advanced, I can use a rusty nail and a coat hanger covered in black tape for a probe with complete confidence in the results.  There's a firmware easter egg that has a video clip of Beavis and Butthead singing "fuck Nyquist and his Theorem."

No, I will not do a teardown.  No, I will not be mailing it to you. 

[heavenfish]

So after 5 pages of this did anyone figure out if Keysight are releasing a new 2000/3000 scope in the next few months?

Well, there is still no industrial competitor for these Keysight scopes from Tektronix or LeCroy.
OK, someone might like WaveSurfer 3000 or Tek MSO2000B.
Keysight has no need to hurry with a new scope model.

Agreed. The only thing not so great of 2k/3k is record length because Keysight uses on chip memory. I don't expect Keysight to change that since it's key to achieve current cost structure. It doesn't make sense to try to design a better but more expensive 2k/3k successor. If keysight had new technology to increase the memory size, sample rate or resolution of the ASIC, why not update the 4k or creat a new 5k product. It certainly will have better return from the investment.

[Wuerstchenhund]

So after 5 pages of this did anyone figure out if Keysight are releasing a new 2000/3000 scope in the next few months?

Well, there is still no industrial competitor for these Keysight scopes from Tektronix or LeCroy.

Of course there are. You said it yourself:

OK, someone might like WaveSurfer 3000 or Tek MSO2000B.

Tek's MSO/DPO2000B is the competitor to the Keysight DSOX/MSOX2000A, and the MDO3000 to the DSOX/MSOX3000A/T. I know, pretty much no-one buys them but still they do exist

The WaveSurfer 3000 is a competitor to the DSOX/MSOX3000A/T and DSOX/MSOX4000A (it sits right between both models), and is actually taking quite a few of the DSOX/MSOX sales. Ever wondered why Keysight bothered to come out with a touch screen version of the DSOX/MSOX3000A?

Keysight has no need to hurry with a new scope model.

No, because most of the DSOX/MSOX models still sell well enough.

[G0HZU]

Dunno if this is of any interest but I did a quick video showing the trace noise/wobble on my old scope when there is an intentionally generated 30dB S/N ratio on the test signal caused by wideband noise.

I scaled it down to 10MHz so to get a 30dB S/N ratio I needed -101dBc/Hz of noise in a 12.5MHz BW.
I produced this noise using a wideband noise source and a step attenuator, a 6dB splitter/combiner and a 12.5MHz LPF. The metal box with all the holes in it is a wideband high level noise source.

12.5MHz BW is 12.5e6 bigger than 1Hz. The marker shows -101dBm/Hz power in a 1Hz BW so the power in that 12.5MHz pedestal is 12.5e6 times bigger.
So the power in the 12.5MHz BW is 10*log(12.5e6) bigger or 71dB bigger.

-101 + 71 = -30dB so the S/N ratio is 30dB. I also checked the S/N ratio using a 20MHz Racal true rms meter and it was close to 30dB.

You can see the noise pedestal on the analyser and then the scope shows how much wobble you see with a 30dB S/N ratio.
I briefly increased the noise to a 20dB S/N ratio on the scope and that causes the brief burst of very bad wobble at 1:02.
Sorry about that, I turned the attenuator the wrong way briefly.

But you see the wobble diminish on the scope when I increase the attenuation to improve the S/N ratio to >= 40dB.
In the last few seconds of the video you can see me swapping back and forth between 40dB and 30dB S/N ratio and the wobble can be seen to almost vanish at the >= 40dB S/N ratio.

If I had done this at 100MHz with a 125MHz BW the wideband noise would need to be at -111dBc/Hz to give this amount of wobble.
If I had done this at 1000MHz with a 1250MHz BW the wideband noise would need to be at -121dBc/Hz.
If I had done this at 3000MHz with a 3750MHz BW the wideband noise would need to be at -126dBc/Hz.

A sig gen set to 3GHz is unlikely to be this noisy unless it was faulty but the scope system noise might be quite high so it might be possible that the cause of the wobble on the Tek scope may be partly due to wideband noise. But it's more likely to be something else IMO.

The video is just a quick and dirty demo so sorry it is so basic and brief...

https://www.youtube.com/watch?v=0vCgQtGJMno&feature=youtu.be

[G0HZU]

The noise source is band limited to 180MHz and I repeated the test with a 180MHz test signal with the 12.5MHz LPF removed from the system. It's as far as I can go with this noise source.

I therefore needed a pedestal of noise at -112.5dBc/Hz in a 180MHz BW to get a 30dB S/N ratio because 180MHz is 82.5dBHz.

When I set the 180MHz BW pedestal of noise down to this level I get the same amount of wobble on the scope on a 180MHz sinewave viewed on the scope. This is because there is the same amount of noise power as in the previous test.

i.e. -101dBm/Hz of noise band limited by a LPF to 12.5MHz BW is -30dBm or 1uW.

-112.5dBm/Hz of noise band limited by the noise source to 180MHz BW is also -30dBm or 1uW.

[G0HZU]

I also tested several of my GHz++ sig gens here for wideband noise floor when set to 2.4GHz and most were OK.
The worst offender was the HP tracking source designed for use with my HP8566B analyser. It gave a noise floor of about -127dBc/Hz right across a 3GHz BW. Not good at all.

The next poor performer was my HP/Agilent ESGD 4433 as this gave a noise floor of about -136dBc/Hz right out to 3GHz when set to 2.4GHz. Not good but the ESGD sig gens are economy sig gens and not really lab grade in terms of noise and spurious.

My other (newer model) ESGD 4433B was several dB better and the Marconi 2024 was much cleaner. The signal source from my E5071B VNA was very clean as well (in terms of broadband noise floor) when set to a cw signal at 2.4GHz. The old HP83752A 20GHz synthesised sweeper I have here was best of all. Very clean and I didn't bother to see how much cleaner. I suspect it is in the order of -150dBc/Hz. This was a nice surprise as I've never tested it like this before and I expected it to be quite noisy.

http://www.keysight.com/en/pd-1000001888%3Aepsg%3Apro-pn-83752A/synthesized-sweeper-001-20-ghz?cc=US&lc=eng

At work we made the mistake of buying some HP8648D sig gens about 12 or so years ago. These have a poorly designed levelling system which means they churn out a very high noise floor when set to levels in the -20 to -10dBm range across the HF/VHF range. Easily 20dB worse than a Marconi 2024. They were eventually banned from the labs because so many people were getting caught out by the high noise level when doing various receiver (and amplifier) tests with them.

[KE5FX]

Interesting stuff, all right.  It does make sense that a 30 dB SNR would cause display jitter on the order of a few percent, enough to be seen on a scope display.  I'd expect a trace jumping around on a scope display to look even worse, since it would be perceived as a "peak to peak" phenomenon.

There would be 95 dB/Hz of excess noise in a 3 GHz bandwidth, and since you've established we can 'see' a 30 dB SNR, a broadband signal source with -125 dBc/Hz or more would indeed be noisy enough to influence the TDS 694C's display.  At offsets beyond 1 MHz the 8672A I used should be in the -140 to -150 dBc/Hz range, so I still don't believe it contributes to the effect seen in the video.  The same is likely true for the aperture jitter of the ADCs in the scope themselves.  Their 10 GHz clock source, on the other hand, is an off-the-shelf ZComm VCO.  It might actually be one of the bigger contributors to the jittery display.

[nfmax]

Interesting. One thing struck me as slightly odd. As far as I can tell from the display (I'm not familiar with this scope model), the scope trigger level was set at 0V, and the delay set at 0s, so the trigger instant should be at the centre of the screen. Yet it was not, the +ve-going crossing was slightly early. Am I mistaken, or is there something wrong?

[nctnico]

This is normal because most oscilloscope triggers will have some hysteresis to avoid triggering on noise. At high frequencies close to the maximum bandwidth it often needs some fiddling with the trigger level to get a stable trigger because the sensitivity of the trigger will be significantly less.

[nfmax]

Agreed. But trigger hysteresis shouldn't affect the trigger threshold - i.e. if I set a threshold at 0.1 division, +ve going, then I would expect the trigger instant to be when the signal rises through the 0.1 division mark. If the trigger hysteresis was set to 0.3 division, I would expect the signal to have to rise to > +0.4 division and then fall to < -0.2 division before a new trigger could be recognised (at the 0.1 divison, +ve going point). Hysteresis shouldn't affect the trigger point.

[G0HZU]

I powered the HP54540C scope up again today and had a look through the settings and found it had a trigger offset of about 40mV programmed in (I think it was 43.75mV). Not sure how this happened but one of my beefs with the scope is that it is really easy to alter something by accident because it has multifunctions on the rotary controls and they are very sensitive. I'm guessing that I knocked the trigger offset away from zero somehow.

I tried doing a Recall CLR to default the scope and the offset now shows zero and the scope triggers in the centre. However, if I go down to 500ps/div the trace is still ever so slightly off to one side. Not sure if this an interpolation issue or if it would go away with a system calibration but I'm not too fussed really. It is only a trace width or so off centre at 500ps/div.

But yes, the scope display was a bit odd in terms of the trigger setting in the video on 50ns/div. You can see it is triggering at the programmed offset that was about 40mV. Sorry about that.

I really don't like scopes with shared controls and I try not to use this scope much. It was a freebie scope salvaged last year from the skip at work.

[Keysight DanielBogdanoff]

This is normal because most oscilloscope triggers will have some hysteresis to avoid triggering on noise.

Yes, you can often see this if you change the trigger mode to "rising OR falling edge." The intersection of the signals won't be right at the 0 time point because the scope can't vertically compensate for both a rising and a falling edge hysteresis offset.  In just rising or just falling edge mode, the scope will position the hysteresis so that the signal comes through the dead center of the screen.

[G0HZU]

At offsets beyond 1 MHz the 8672A I used should be in the -140 to -150 dBc/Hz range, so I still don't believe it contributes to the effect seen in the video.

Yes, the HP8672A looks like a decent generator. I've not used one but the specs look good and it would have to be faulty to generate that much broadband noise. When I tested my HP54540C up at 600MHz with several sig gens here I took the precaution of using a very narrow 600MHz BPF inline just to be safe but it made no difference with/without the filter as the scope only has 500MHz BW and my regular sig gens are all clean enough for this test.
When tested at 600MHz this scope is beyond the 500MHz -3dB BW stamped on the front panel but it is still just inside -3dB at 600MHz when tested. It shows a fair bit of wobble on the sine wave when tested up here though. Very similar to your Tek scope display.

[siggi]

Dunno if this is of any interest but I did a quick video showing the trace noise/wobble on my old scope when there is an intentionally generated 30dB S/N ratio on the test signal caused by wideband noise.

On a tangent, it should be possible to get an idea of the noise characteristics of the front end of the TDS scopes by looking at the signal feed-through. My TDS784D has channel 3 fed through to the back. Looking at the spec, though, man: "11mV/division +-20% into a 50Ohm load.", that's pretty loosy-goosy.

It also looks like the 694C doesn't have that feed-through.

[G0HZU]

I took a quick video of my HP54540C (500MHz BW and 2GS/s) with it trying to measure the 500Hz squarewave test waveform from the scope. This waveform can be used to set up the probes on the scope etc.

It has a very fast edge on the waveform and you can see in the video that 2GS/s isn't a high enough sample rate because you can see overshoot/wobble when sampling at 2GS/s. It gets even worse at 1GS/s.

However, the waveform cleans up nicely when the Repetitive mode is selected. The waveform loses the undershoot on the start of the leading edge and just looks better.

So in this case, having a scope branded as having 500MHz BW and sampling at 4 times the BW isn't enough to prevent waveform issues. There aren't enough samples to prevent corruption from aliasing.  This waveform is a 500Hz squarewave but it has frequency content that goes well above 1GHz. The Repetitive mode has a much higher effective sample rate and so this gives a much nicer result.

It's taken with a mobile phone so it is a bit flakey but I think it is clear enough from this demo that there are times when a 4:1 sample rate to BW ratio isn't enough when you feed a real signal to a real scope

Note that there is a trigger offset on this video again. I used default and autoscale to set up the scope and set CH1 to 50R input. But it has added an offset again so it doesn't trigger in the centre.

https://www.youtube.com/watch?v=8yz662DeElA&feature=youtu.be

I also looked at the test signal on a spectrum analyser and it shows frequency content that extends well above 1GHz. This should be no surprise as the risetime of the waveform is probably less than 500ps. Too fast for this scope to measure accurately. But the lowpass filtering in the analogue front end of the scope isn't steep enough to prevent the >1GHz frequencies from reaching the sampler stage in the scope.

[nctnico]

If this scope has equivalent time sampling then it doesn't surprise me the analog front end filter doesn't roll off very steep (probably a Gaussian response).

[G0HZU]

I think some of the wobble effect is from the interpolation when in real time mode. I'm guessing that the fast risetime means that the interpolation can't cope very well with the limited qty of samples. So you get a wobbly effect and the introduction of the negative bump at the start of the leading edge?

[nctnico]

When the frequency contents get close to fs/2 (say >0.42 fs) then the interpolation could get upset.

[G0HZU]

It wobbles on a clean sinewave at 600MHz with 2GS/s as well and this is well below Fs/2. It basically looks the same as the Tek scope. I've seen this on other scopes at work too.

A real scope like this one will have noise, (and maybe alias terms on complex signals) and sampling/timing jitter to cope with. It will have real world filters in it and this will all mean that the interpolation result will reflect all these factors. So you can't expect it to draw an accurate sinewave once you get this high in frequency.

It's going to affect the amplitude and also it will introduce distortion into the overall shape of the sinewave.

[HackedFridgeMagnet]

With the release of the new R&S RTB2000 series hopefully Keysight will bring out something soon.

I'm wanting to buy very soon, is it worth waiting Keysight?