Author Topic: Oscillo-confusion MHz GSa/s wfm/s Mpts  (Read 9939 times)

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Offline FriedMuleTopic starter

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Oscillo-confusion MHz GSa/s wfm/s Mpts
« on: December 31, 2018, 02:14:55 pm »
When trying to find the "best" scope for the money, I stumble over all sort of technical data as sample rade, memory depth, bandwidth and a lot more.
350Mhz 14M wms/s or 200Mhz 140M wms/s and so on, what is important and why (MHz - GSa/s - wfm/s - Mpts or ??? :-)
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Offline tggzzz

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #1 on: December 31, 2018, 02:40:55 pm »
Bandwidth and samples/second are completely independent. Bandwidth is all that matters in a scope, except to salesmen. I have an ~4GHz scope with ~40kS/s.

Apart from that fundamental, there are many threads on "scopes for beginners" on this forum.

The key points are to define what you will use the scope for, and whether you have other necessary equipment. Plus you shouldn't forget the cost of probes :)
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Offline mvs

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #2 on: December 31, 2018, 03:46:31 pm »
Bandwidth and samples/second are completely independent. Bandwidth is all that matters in a scope, except to salesmen. I have an ~4GHz scope with ~40kS/s.
Equivalent time sampling scopes work with repetitive signals only.
For general use one needs both ADC with fast sampling speed and analog frontend with high bandwidth.
 

Offline tggzzz

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #3 on: December 31, 2018, 04:54:43 pm »
Bandwidth and samples/second are completely independent. Bandwidth is all that matters in a scope, except to salesmen. I have an ~4GHz scope with ~40kS/s.
Equivalent time sampling scopes work with repetitive signals only.
For general use one needs both ADC with fast sampling speed and analog frontend with high bandwidth.

Of course.

Your statements, while correct, neither conflict nor change my statements.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline helius

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #4 on: December 31, 2018, 05:10:43 pm »
Those are only the headline specs! Depending on what you need to do, there are many more things that can matter, like sensitivity, ENOB, blind time, channel-to-channel matching, and more picayune stuff like measurements, math functions, fft, go/no-go, etc etc
 

Offline tggzzz

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #5 on: December 31, 2018, 05:21:45 pm »
Those are only the headline specs! Depending on what you need to do, there are many more things that can matter, like sensitivity, ENOB, blind time, channel-to-channel matching, and more picayune stuff like measurements, math functions, fft, go/no-go, etc etc

... hence the third sentence in my original reply, viz "the key points are to define what you will use the scope for, and whether you have other necessary equipment" :)
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline rstofer

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #6 on: December 31, 2018, 06:45:21 pm »
When trying to find the "best" scope for the money, I stumble over all sort of technical data as sample rade, memory depth, bandwidth and a lot more.
350Mhz 14M wms/s or 200Mhz 140M wms/s and so on, what is important and why (MHz - GSa/s - wfm/s - Mpts or ??? :-)

Define the money first!  There is no way in the world that a $350 Rigol DS1054Z is on the same planet with a $200k Keysight.  If you aren't in the market for the Keysight, what does it matter how good it specs out?

Bandwidth is up to you.  What do you want to see?  If it is a sine wave at 100 MHz, then a 100 MHz scope will do.  If it is a square wave at 20 MHz and you think seeing only up to the 5th harmonic is good enough, a 100 MHz scope will do.  Remember, that square wave has harmonics from DC to daylight.  How many need to be displayed?  What happens is that the square wave looks more like a sine wave as the frequency is increased and the ability to display a lot of harmonics is decreased.

Remember the number 2.5, there will be a test later.  The industry standard seems to be to sample at 2.5 times the maximum signal frequency - minimum.  Technically, 2 would get it done under ideal circumstances but the industry has chosen 2.5

DS1054Z - 4 channels times 100 MHz times 2.5 => 1 GHz sample rate.  It all lines up!  If all of the channels aren't in use, the 2.5 number can be increased.  1 channel times 100 MHz times 10.0 => 1 GSps on just one channel.  Sampling at 10x will produce a better display than sampling at 2.5x but what you see on the screen is really just a drug induced hallucination in any event.  There's a lot of interpolation going on down inside that FPGA.  On some scopes you can just display the samples as dots without a line and magic interpolation.  I don't know what use that is.

Page 10 here for record length and waveforms per second (neither of those specs are particularly important to me):

http://ecee.colorado.edu/~mcclurel/txyzscopes.pdf

Clearly, more of anything is better than less.  The real questions are "Does it matter?" and "Can I afford it?".

There is no such thing as 'best for the money' if money is also a variable.  It's better to drive a stake in the ground ("I won't spend more than $xxx, no matter what!") and work back from there.  A more expensive scope will almost always be a better scope.

For entry level scopes, the DS1054Z and the Siglent SDS1104X-E seem to be popular.  The Siglent is newer and the user interface is said to be much faster than Rigol's.  If I didn't already have the DS1054Z, I would be looking at the SDS1204X-E 200 MHz, 4 Channel.  Or unlocking a SDS1104X-E to get the bandwidth.  See the "Test Equipment" forum here on EEVblog.
 

Offline FriedMuleTopic starter

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #7 on: December 31, 2018, 07:29:01 pm »
Your answers are all great! :-)
Hmm what I will use it for... It shall be my main scope used for whatever I find interesting. Both digital, analog and whatever. I know that this not an answer but I do not know what I will play with in 5 years from now.

I am now looking at the
Siglent SDS1204X-E 200Mhz 1 GSa/s

but may be willing to buy the
Siglent SDS2352X-E 2Ch 350MHz 2 GSa/s

But 800$ is my limit! :-)

Why Siglent, no fantastic reason but I like the interface, functions and the price.
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Offline schmitt trigger

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #8 on: December 31, 2018, 07:37:53 pm »
In addition to the valuable information already provided:
Please note that the quoted bandwidth is usually @ -3dB down.
 

Offline rstofer

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #9 on: December 31, 2018, 07:49:14 pm »
Your answers are all great! :-)
Hmm what I will use it for... It shall be my main scope used for whatever I find interesting. Both digital, analog and whatever. I know that this not an answer but I do not know what I will play with in 5 years from now.

I am now looking at the
Siglent SDS1204X-E 200Mhz 1 GSa/s


This is the latest "shiny thing".  It is the scope I would buy had I not bought the DS1054Z a while back.  In fact, I am thinking of dedicating the 1054 to my analog computers as an excuse to buy it anyway.

Quote
but may be willing to buy the
Siglent SDS2352X-E 2Ch 350MHz 2 GSa/s

But 800$ is my limit! :-)


I get my 350 MHz needs satisfied by an old Tektronix 485 I bought used 12+ years ago for about $200.  The Rigol is more fully featured and I want 4 channels more than I want bandwidth so the 1054Z is a good fit.  The most important spec for a scope is bandwidth - except channels.

In the micro world, decoding SPI is easier with 4 channels.  Yes, the logic analyzer might be better but it won't give any indication of signal integrity and things like setup and hold times may not be accurately displayed due to the relatively low sample rate.

Since I already had bandwidth, I bought the Rigol for DSO features like channels, decoding, single shot (MOST important), measurements, etc.  All the things that a DSO brings to the dance that an older analog scope simply doesn't have.

Quote
Why Siglent, no fantastic reason but I like the interface, functions and the price.

No reason why not!  Check for particular models in the "Test Equipment" forum here on EEVblog.
 

Offline FriedMuleTopic starter

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #10 on: December 31, 2018, 09:50:42 pm »
How important would you mean that 4CH is compared to 2CH for everyday use?
I think that a later 4CH analog scope could be a good addition?
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Offline rstofer

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #11 on: December 31, 2018, 11:02:57 pm »
How important would you mean that 4CH is compared to 2CH for everyday use?
I think that a later 4CH analog scope could be a good addition?

I bought the DS1054Z because a) it had 4 channels and b) I could afford it.  I already had a 350 MHz Tek 485 but it was only 2 channels.  The DSO measurements are handy but I could do without them.  So, in the end, the decision was for 4 channels.  SPI bus...

There's at least one thing a DSO can do that an analog scope can't and that's single shot capture.  If a signal comes along every day or two and I can figure a way to trigger on it, I can come back a week later and the image will still be on the screen.  I realize the time scales are ridiculous but the idea is the same.  An event happens, I trigger and capture it.  It doesn't need to be a repetitive signal to accommodate an analog scope and I don't have to try to buy an analog storage scope.

It is impossible to overstate the importance of single shot mode.

There are just too many advantages to the DSO.  Yes, the analog scope has a place (mine is under the bench) but most people will be well served by the features of a modern DSO.  If they need an analog scope, they'll know why they need it!

All that said, I got along with 2 channel scopes since I gave up on a 1 channel scope decades ago.  Somehow I was able to troubleshoot SPI without 4 channels.  And I could do it without single shot mode.  And I got along without all the measurements.  Everything worked out fine!  But it's just so much easier with a 4 channel DSO.
 

Offline rstofer

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #12 on: December 31, 2018, 11:08:04 pm »
There is certainly something to be said for the idea that 2 channels are sufficient.  For just about everything, 2 channels is just fine.  I hardly ever use all 4 channels simultaneously.  But they're there when I want to work on something like SPI which just happens to be my favorite serial protocol.

Yes, things get done with 2 channel scopes.  But there are some things that really take advantage of 4 channels.  The question is: "What are they worth to you?".  To me, the 4 channels was the only reason to buy the DS1054Z.  I could get along without single shot mode.  But I don't have to!
 

Offline FriedMuleTopic starter

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #13 on: January 01, 2019, 01:31:23 am »
So would you buy a 4ch 200MHz 1GSa/s or a 2ch 350MHz 2GSa/s for "whatever use"?
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Offline tggzzz

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #14 on: January 01, 2019, 01:44:30 am »
So would you buy a 4ch 200MHz 1GSa/s or a 2ch 350MHz 2GSa/s for "whatever use"?

For "whatever" == "signal integrity", go for 350MHz since it is higher than 200MHz. Add cost of probes of course, for every channel

For "whatever" == "protocol decode", go for a logic analyser, since it is much cheaper, is faster, and is more flexible and powerful in the digital domain.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline basinstreetdesign

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #15 on: January 01, 2019, 01:46:02 am »
So would you buy a 4ch 200MHz 1GSa/s or a 2ch 350MHz 2GSa/s for "whatever use"?

I've seen this question before and my answer is still the same.  Given a choice between one scope with an extra two channels for extra $200 and a scope with extra 100 MHz bandwidth for only $100 more I would take the extra two channels in a heartbeat.  There are fairly few situations where an extra 100 MHZ would make much difference but many times an extra two channels can make a testing situation MUCH easier.  The extra channels will give you MUCH more information on a situation than being able to see a pulse or an edge with a bit more precision.
« Last Edit: January 01, 2019, 01:47:40 am by basinstreetdesign »
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Offline FriedMuleTopic starter

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #16 on: January 01, 2019, 02:06:59 am »
So it is not so easy after all:-)
I am in no way doubting  any of your answers, just trying to understand.

basinstreetdesign the difference is 150MHz and 1GSa/s more and about twice the money.

tggzzz  how often and to what would you say that faster is better then twice the channels and where not?
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Offline james_s

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #17 on: January 01, 2019, 07:22:09 am »
It's easy to get paralyzed with indecision, but you can think of it another way. These are relatively low cost instruments being discussed here, it's not exactly impulse buy territory for most people but it isn't a major life decision either. Some day down the road you can upgrade to a fancier scope if you end up needing it. Take good care of whichever one you buy and it will likely hold a good portion of its value, if you decide you don't like it, you can sell it to someone else.
 

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #18 on: January 01, 2019, 08:01:24 am »
So it is not so easy after all:-)
It’s not hard either.
For hobbyist use a SDS1204X-E is an excellent choice, sufficient memory depth, sampling, WF/s, all the I/O’s you might need and priced well enough to allow change left to get things like a dedicated AWG.
You might even get the cheaper 1104X-E and if needing additional BW apply one of the cracks to it to soup it up to the the 200MHz model.

The SDS2352X-E will be a better GP scope but primarily for the higher BW it offers......it’s not so much the scope but knowing how to drive it.  ;)

My 2c, get the SDS1104X-E.
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Offline tggzzz

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #19 on: January 01, 2019, 09:56:13 am »
So it is not so easy after all:-)
I am in no way doubting  any of your answers, just trying to understand.

tggzzz  how often and to what would you say that faster is better then twice the channels and where not?

To simplify, either 0% or 100%, depending on what you are trying to achieve. There's a hint there :)

Once you have defined what you are trying to achieve, you can match different tool's characteristics to the job at hand.

I designed and built my first computer in the mid 70s (6800 + 128bytes RAM + TTL) mostly using switches, LEDs, and a multimeter. One one occasion I used a scope for 10 minutes, to check the critical clock waveform. In that 10 minutes I learned that probing technique is critical and that 6" ground leads are a problem :)

More recently for digital circuits I use a logic analyser, printf() statements and the debugger with an IDE. But only after I have checked that all the analogue signals will be interpreted correctly as digital signal (i.e. setup/hold, clean transition, voltages). The key is to plan implementation so that each stage is known to be correct before the next stage is implemented.

Look at my .sig, and replace "gliding" and "span" with "electronics" and "scopes" :)
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline FriedMuleTopic starter

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #20 on: January 01, 2019, 02:58:28 pm »
So the smartest would be to find out if Siglent or other makes 4ch version of the 350MHz?
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Offline tggzzz

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #21 on: January 01, 2019, 04:54:10 pm »
So the smartest would be to find out if Siglent or other makes 4ch version of the 350MHz?

You can always throw money at a "problem" :)

i suspect the smartest thing is to (1) define a project (2) define what needs to be tested and the classes of tools that can do that (3) buy a cheap example of each class.

You will make mistakes, learn a lot, and then be in a position to know what you really need.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline FriedMuleTopic starter

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #22 on: January 01, 2019, 07:33:47 pm »
Great advice, I know that SMPS, linier supplies, amplifier, d/a convertere, bluetooth and that kind is what I am interested in rght now.
My thought by buying a good scope now, was that I then only have to buy a scope once in the next many years instead of a cheep now that I need to change in 2 years.
I was thinking of buying a great beginner scope now and if I ever need to, then buy a 500MHz-1GHz 4 channel analog scope later on to use when the normal scope is not enough.
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Offline james_s

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #23 on: January 01, 2019, 07:39:13 pm »
I think that's a reasonable approach. The thing is, there are lots of great beginner scopes now, it's really hard to go wrong as long as you avoid the very low cost toy scopes like those pocket models you can get for <$100. Any one of the popular entry level DSOs mentioned here will likely do what you need so just pick one and then focus on learning to make the most of it, remembering that for decades engineers designed incredibly sophisticated machines using scopes less capable than the $350 DSOs you can get now.
 

Offline rstofer

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Re: Oscillo-confusion MHz GSa/s wfm/s Mpts
« Reply #24 on: January 01, 2019, 08:40:11 pm »
There is still the possibility that for high bandwidth you don't need the features of a DSO.  They're handy but not really necessary.

For things related to microcontrollers and FPGAs (and certainly audio and SMPSs), the external speeds are usually 50 MHz or less.  SPI, which I might want to decode, is probably running at 20 MHz or less.  The DS1054Z (unlocked to 100 MHz) handles that well.  I get all the bells and whistles for lower frequencies for a really low price.

Then for the faster stuff, I still have the analog scope.  I could also buy a used 500 MHz scope for something on the order of $800.  But only when I need it.  Of course, I already have a 350 MHz scope but if I didn't, that's an approach I would take.

Buy the lower bandwidth DSO for the bells and whistles and buy a high bandwidth analog scope later, if ever.

It seems like the extra cost of a higher performing scope in early times would take away money from everything else.  Bench meters, handheld meters, function generator, lab power supply, etc.  There's only so much money to go around and each of those tools needs to be represented on the bench.

Or maybe money isn't the issue.  That's not my situation!

 


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