Evaluating oscilloscopes for best waveform update rates

[pascal_sweden]

I found a nice application note from Keysight about waveform update rates in scopes.
The document describes it very well, and I therefore wanted to share this, as waveform update rate is a common subject for discussion on this forum

http://www.keysight.com/main/redirector.jspx?action=ref&cname=EDITORIAL&ckey=1374518&lc=eng&cc=NO&nfr=-11143.0.00

In addition, I also found a nice video from Rohde & Schwartz about how mask testing in a scope can really slow down the waveform update rate, unless the implementation is done in hardware:

http://rohde-schwarz-scopes.com/scope_lie_03.php

The waveform update rates in the Agilent InfiniiVision Series are not affected when you are using logic acquisition channels and/or serial bus decoding, next to the scope channels.

But what about mask test measurement? Mask test measurement, is one of the more demanding scope measurement tests and would slow down the update rate of most digital oscilloscopes.

[Someone]

The mask is stored in a memory layer as an overlay, its compared in realtime to the display binning. A quick google offers many references to 280,000 tests per second maximum rate.

[Wuerstchenhund]

I found a nice application note from Keysight about waveform update rates in scopes.
The document describes it very well, and I therefore wanted to share this

I guess most people know Agilent's/Keysight's whitepaper by now, especially after waveform update rates and this document have been extensively discussed two or three years ago in this forum already after Agilent came out with their (at that time new) DSOX2000 Series. You probably might want to use the search function to find that thread, as it probably answers a lot of any questions you might have.

Also, don't make the (common) mistake of taking these "whitepapers" as facts. Especially Agilent/Keysight has a long track record of twisting facts up to borderline lying, and most brands use these "whitepapers" as marketing tools to sell their stuff. Agilent/Keysight are the worst, but others like Tek aren't that much better.

Same goes for R&S's videos. Mask testing should be a snap for any decent newer scope.

[tautech]

There's significant discussion on waveform update rates early in and throughout the first Siglent SDS2000 thread. Starting from Marmad's post nearly 2 years ago:
https://www.eevblog.com/forum/testgear/siglent's-new-product-msosds2000-series/msg319885/#msg319885

[pascal_sweden]

Thanks for pointing out the discussion!
I will read through that thread when I have some more time in the coming week.
Will come back with any outstanding or new questions afterwards

[nctnico]

Also don't forget update rates assume you can keep your eyes open and stay focussed 100% of the time. In other words: a cleverly setup trigger is often more effective for capturing events which occur every now and then. You can set it up in the morning and come back at the end of the day to see the results (segmented recording may be handy).

[Wuerstchenhund]

Also don't forget update rates assume you can keep your eyes open and stay focussed 100% of the time.

Exactly. Plus, just because you can see a rare glitch appear doesn't mean you know anything about it (i.e. its parameters).

In other words: a cleverly setup trigger is often more effective for capturing events which occur every now and then. You can set it up in the morning and come back at the end of the day to see the results (segmented recording may be handy).

Indeed. With the right trigger setup you can capture and analyze the glitch parameters, which usually helps a lot to find the culprit.

[pascal_sweden]

How to check the waveform update rate with the external trigger output?
Does this work on most scopes? How accurate is it?

[Wuerstchenhund]

How to check the waveform update rate with the external trigger output?

Connect a counter to it and off you go 

Does this work on most scopes?

Pretty much on any scope that has trigger out.

How accurate is it?

Very accurate, as trigger rate = wfm rate

[Mark_O]

Also don't forget update rates assume you can keep your eyes open and stay focussed 100% of the time.

Exactly. Plus, just because you can see a rare glitch appear doesn't mean you know anything about it (i.e. its parameters).

An even more important corollary is that just because you don't see a glitch (regardless of the excellent waveform update rate of your scope), doesn't mean one isn't there.

[Wuerstchenhund]

Also don't forget update rates assume you can keep your eyes open and stay focussed 100% of the time.

Exactly. Plus, just because you can see a rare glitch appear doesn't mean you know anything about it (i.e. its parameters).

An even more important corollary is that just because you don't see a glitch (regardless of the excellent waveform update rate of your scope), doesn't mean one isn't there.

You're right of course. Which is why every somewhat decent DSO comes with a wide range of triggers that allows you to capture any signal deviation, visible or not visible.

[rf-loop]

But what about mask test measurement? Mask test measurement, is one of the more demanding scope measurement tests and would slow down the update rate of most digital oscilloscopes.

Example in Siglent SDS2000.  Mask test do not reduce waveform update speed at all and is maximum 110 kwfm/s. No matter if test result pass or fail.  It is HW based function.  Yes, we can see it reduce speed in many low end scopes and older technology scopes. Example Rigol DS1000Z it is extremely slow. Mask test  totally freeze it to <5 waveform/s if test result is fail.  Also in example Siglent SDS1000DL/CNL/CML models it is quite slow.

[pascal_sweden]

What about the higher Rigol series? DS2000A series or DS4000 series?
Do not of these have the mask test function or decoding function in hardware?

I have seen a video about the DS4000 series which becomes extremely slow during protocol decoding.
This makes me conclude that everything is done in software.

However I have not seen, or might have missed a video about the mask testing on higher end Rigol series, such as Rigol DS2000A and Rigol DS4000 series.

Do you have more details about the hardware functions that are available in the Siglent SDS2000 series?
Are we talking about more functions than the mask test function? E.g. protocol decoding functions, hardware triggers, etc.

[nctnico]

Also don't forget update rates assume you can keep your eyes open and stay focussed 100% of the time.

Exactly. Plus, just because you can see a rare glitch appear doesn't mean you know anything about it (i.e. its parameters).

An even more important corollary is that just because you don't see a glitch (regardless of the excellent waveform update rate of your scope), doesn't mean one isn't there.

You can always turn catching a glitch into teamwork:

Or use a magnifier glass:

[H.O]

What about the higher Rigol series? DS2000A series or DS4000 series?

Just did a test on my DS4000:
1MHz Square wave into channel 1, 10ns per div. Mask as in attached screenshot. Trig out to external frequency counter.



Without the Pass/Fail test enabled it does ~91k waveform updates per second. Enabling the Pass/Fail makes it drop to 50k waveform updates per second. I confirmed this by letting it run for 60 seconds, as the screenshot shows it processed ~3million waveforms - all passed.

However if I, for example, change the amplitdue of the incomming signal so that test fails continously then the update rate drops to about 1 per second (yes one). I don't really know what's up with that.

[rf-loop]

However if I, for example, change the amplitdue of the incomming signal so that test fails continously then the update rate drops to about 1 per second (yes one). I don't really know what's up with that.

And this is just same what happend also with Rigol DS1000Z in my tests. 
This make it extremely poor if need analyze signal pass fail ratio.
If I have pulse output for example 50000 pulses/s  and randomly around 1 pulse / s fails.   If this continue and I read how many fails and how many pass, well result is total junk and I need take other tool for analyze this simple case if I regognize this "feature". 
So, before trust test instrument results, know your equipment...

(In Siglent SDS2000,  there is same speed if pass or fail.  Just full wfms/s, same what is without pass/fail mask test.)