Digital oscilloscope - behind-the-scenes presentation - Page 1
Forum section: electronics / testgear

author: isometrik
author_rank: Regular Contributor
timestamp: August 23, 2017, 02:44:02 pm
content: James Lewis (BaldEngineer.com) gave a talk in July 2017 about the inner workings of DSOs. Having learned quite a bit from his presentation, I thought other members of the community might be interested.Have a look if you would like to learn some of the intricacies of modern DSOs:https://www.baldengineer.com/videos/top-of-the-pacq-oscilloscope-talk

author: karkoon
author_rank: Contributor
timestamp: August 23, 2017, 03:52:51 pm
content: Thank you for posting. Learned a lot.Sent from my iPhone using Tapatalk

author: rsjsouza
author_rank: Super Contributor
timestamp: August 23, 2017, 04:38:01 pm
content: Thanks. I saved this link to watch later.

author: Keysight DanielBogdanoff
author_rank: Unknown
timestamp: August 23, 2017, 06:49:22 pm
content: If I may, here's the video series of ours he referenced that was a talk from one of our ADC designers:

author: bjcuizon
author_rank: Frequent Contributor
timestamp: August 23, 2017, 07:55:10 pm
content: Quote from: Keysight DanielBogdanoff on August 23, 2017, 06:49:22 pmGo to keysight's YT channel as there is much to learn in there. I think they did around 5 videos (if memory serves me right) about the hardware design. (They're all about what is behind the BNC)*I am not affiliated with Keysight in any way. I just like how they teach stuff.

author: ez24
author_rank: Super Contributor
timestamp: August 23, 2017, 08:35:10 pm
content: Very strangeI added this channel to the YT Listhttps://www.eevblog.com/forum/other-blog-specific/dd/msg1093983/#msg1093983BUTI cannot see the number of subs. I left the field blank and a "0" was inserted. I will change it when I find the number of subs. Another strange thing is it seems the owner does not want people to find their videos because of the strange titles the videos have. Another strange thing is there is no Menu. Normally there is a Home, Videos, Playlist and About tabs. But I do not see any. This is the second time (out of hundreds) that I have come across this.I am not even sure there are 10 electronic videos ? If there are complaints, I will delete them from the list.

author: baldengineer
author_rank: Contributor
timestamp: August 24, 2017, 03:15:36 am
content: Thanks for posting!If anyone has questions, I'd be happy to answer here.

author: ez24
author_rank: Super Contributor
timestamp: August 24, 2017, 03:57:47 am
content: Quote from: baldengineer on August 24, 2017, 03:15:36 amWelcome and thanks for making the videoCan you tell me how many subs this channel has? What does the title mean?thanks

author: tautech
author_rank: Super Contributor
timestamp: August 24, 2017, 05:36:04 am
content: Quote from: baldengineer on August 24, 2017, 03:15:36 amJames, @~35 mins you state that a R&S scope a couple of years ago was the first to be released with a digital trigger. Was that before 2013 ?If not then you best read this:http://www.siglentamerica.com/qyxwxx.aspx?id=919&sid=25

author: Markus@RohdeScopes
author_rank: Contributor
timestamp: August 24, 2017, 06:40:29 am
content: Quote from: tautech on August 24, 2017, 05:36:04 amWe introduce the RTO on June 2010. It has this trigger system.Markus

author: tautech
author_rank: Super Contributor
timestamp: August 24, 2017, 07:40:19 am
content: Quote from: Markus@RohdeScopes on August 24, 2017, 06:40:29 amThanks Markus, James went on like it was a new thing which of course it's not.

author: ADT123
author_rank: Regular Contributor
timestamp: August 24, 2017, 08:09:20 am
content: Pico introduced digital triggering in 1991https://www.evaluationengineering.com/special-reports/201401/instruments/Stop-on-Trigger.htmlAnyone with an earlier claim?Nice video BTW.

author: isometrik
author_rank: Regular Contributor
timestamp: August 24, 2017, 01:08:16 pm
content: Thank you James (baldengineer) for the great talk, and thank you Daniel (Keysight DanielBogdanoff) and bjcuizon for the supplemental videos.

author: b_force
author_rank: Super Contributor
timestamp: August 24, 2017, 07:38:27 pm
content: Very interesting, especially about the fact that with standard/default settings a scope actually is less accurate if talking about measuring the frequency, and therefor the user actually needs to 'zoom in'.Which is very counter intuitive, because normally (analog) you will get a better average when considering more periods of a signal.

author: tautech
author_rank: Super Contributor
timestamp: August 24, 2017, 09:22:36 pm
content: Quote from: b_force on August 24, 2017, 07:38:27 pmI wonder if James was referring to this thread where you can clearly see the difference between different scope models and their measurement accuracy.https://www.eevblog.com/forum/testgear/testing-dso-auto-measurements-accuracy-across-timebases/

author: MrW0lf
author_rank: Frequent Contributor
timestamp: August 24, 2017, 10:20:16 pm
content: About this Rigol-thing and other "pixel measuring" scopes. If move to scope like this from CRO - maybe improvement. After all many digital wonders still work. Might be WTF moment if move from scope that does non-decimated or at least large dataset measurements... because it's not in the spec and one may indeed presume normal statistical behaviour where more wfms = more accurate measurements. Scope can be surprisingly accurate when combine digital trigger and non-decimated measurements. Was not far off from femtoseconds with some experiments on cheap scope.Overall question is - is thereexcusefor "pixel measuring" scope to exist in 2017 and be a good buy? I would say only if it offers mind-boggling performance in glitch hunting for person that specifically needs it. Or ifverybudget stretched... For general usage non-decimating scope is much more versatile tool, especially if user has full control over used memory size, sample rate etc and can still optimize for speed when needed. Might be surprise for some that scope models like this actually outnumber "pixel counters" and it's not common practice, but actually specific to small number of brands and model lineups.

author: 2N3055
author_rank: Super Contributor
timestamp: August 24, 2017, 10:52:44 pm
content: Quote from: MrW0lf on August 24, 2017, 10:20:16 pmThere is no difference in results of statistical analysis over one long capture or several repetitive trigger events.. Most people zoom in to a part of waveform they are interested in, and then let scope gather statistical average over number of trigger events...Picoscope works with a logic of data acquisition board.. Get big sample for analysis. I believe LeCroy has similar logic behind.. Other scopes are more centered around triggering and repetition.. Both are valid for different type of work. Long memory is good for when you are searching for a problem you don't understand. So you capture long capture and analyze it for anomalies.. For that to be really useful you need good analysis tools on a scope.. But it is great, you can search for dozen different things on a same capture..When you want to trigger on a problem, you need to have some idea what a problem is... And if you triggering on a runt, you don't see other anomalies... But it is quick, it directly captures the problem... No need for analysis...So both have it's use.. And ideally, you should have both capabilities...

author: MrW0lf
author_rank: Frequent Contributor
timestamp: August 24, 2017, 11:35:26 pm
content: Quote from: 2N3055 on August 24, 2017, 10:52:44 pmActually with true "pixel counter" this does not work because it's not just decimating but actually modifying true sample points to match screen matrix. It's irreversible process. Sign of this is silly values for standard deviation (like 0) and "statistical" data having discrete steps that approx match screen resolution. Among other things this results in non functional RMS measurements, problems with integration/derivatives etc.When in doubt try to measure duty cycle on slow signal with 6+ digit accuracy, <10kHz for example. Impossible in principle: when fit it to screen edges of signal get "pixelated" and lose true sample timings. This cartoon then gets chewed thru stats engine which will only stabilize discrete stepped value, not regain accuracy.

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2017, 07:42:01 am
content: Hi.Quote from: MrW0lf on August 24, 2017, 11:35:26 pmWell that is definition of decimation... Nothing wrong with that, all scopes do exactly that when translating data for screen. Fact that DS1000Z uses that for measurements is unfortunate, because some measurements would have better resolution if it used data set with better time resolution. And it is not modifying data samples, they stay intact in acquisition buffer, until next trigger event or clear.Quote from: MrW0lf on August 24, 2017, 11:35:26 pmTrue RMS is one of measurements that would benefit if DS1000Z didn't use such a small sample subset. When used on a repetitive waveform, you can "zoom in" with timebase to get several periods on screen, it will measure fine, within it's 3% accuracy anyways.... But if you have noise or some irregular signal with large high frequency content, or pulses with high on/off ratio, it is crap.. And that is a problem sometimes.Reason for this is that by using 600 data points (or whatever it is exactly) for measurements, you get fixed effective sampling rate of 1/60th of timebase (10ms/div would be 6 kHz effective sample rate), regardless of sample buffer size and real sample rate... It will act as a low pass filter , and filter out all higher frequency content..Going with larger and larger subset would at one point reach declared accuracy (3%) and at one point increasing number of points would reach the point of diminishing returns.. That's why most scopes also work on a subset, but a larger one and have good results..Quote from: MrW0lf on August 24, 2017, 11:35:26 pmGood luck with 6+ digits accuracy on a instrument that has stated +-50 ppm timebase accuracy... If the signal is so repetitive and stable that you can extract meaningful timing data from 10s of thousands averages to 6+ digits accuracy, timer/counter is the instrument to do so.... That's what I use for that kind of measurement..But I agree, in this case Picoscope will extract more meaningful data than DS1000Z (4-5 digits maybe) and would be much better instrument for that measurement..That's why I have both...And will be getting better scope in foreseeable future, because they are both limited in many ways.. And will keep both DS1000Z as great carry around work scope, and 12Bit Pico as specialist instrument for low level measurements and analysis...Take care..

author: MrW0lf
author_rank: Frequent Contributor
timestamp: August 25, 2017, 08:15:50 am
content: Quote from: 2N3055 on August 25, 2017, 07:42:01 amNear 100MHz (on 2408B) it's indeed more like 5 digits, however sub-MHz 7 digits is no problem...512 averages used. Worst error in pictured test was 1.165ps offset, which is in ballpark with claimed 3ps RMS sample jitter. Since it's good sport might try audio range and see what get in the eveningOtherwise excuse getting little fired up but Mr Baldengineer first claims in video that auto-measurements are all the rage, no need for grid even, and then defends case for"pixel counters"...

author: MrW0lf
author_rank: Frequent Contributor
timestamp: August 25, 2017, 03:16:01 pm
content: Input: Siglent SDG2000X, TrueArb, 4577.637Hz square, 96% dutyMath checkppw=1/f*duty=209.715usSecond SDG2000X unit, counter, HFR=ON:f=4577.6370Hzppw=209.756usduty=96%TTi TF960 @ 100s setting:f=4577.63813Hzppw=209.70usduty=96%AD2 @ 33.333MSa/sf: 4577.70Hzppw: 209.704usduty: 95.9961%PicoScope 2408B @ 1GSa/s:f=4577.657Hzppw=209.7056us (cursors: 209.7056us)duty=95.996%PicoScope 2408B @ 9.615MSa/s:f=4577.651Hzppw=209.7059usduty=95.996%Measuring freq this low is quite nasty and seems to scratch some internal limits of math engine on scope (2408B), so no low picosecond accuracy like on higher freqs. However counter did beat it only in freq measurement. Performance with duty and pulse width is about equal. Seems even little better with scopes.Scope performs essentially same on high sample rate and very low sample rate. With high rate only few captures needed, while with low rate proportionally more to achieve statistical gain. All by the book.So when scope has good math engine operating on true sample points there is not exactly huge need for separate counter unless want >6 digits. If this scope is USB or desktop is matter of taste. Would be actually interesting to see similar tests on desktop scopes. AFAIK from cheap ones GWI and Siglent should perform quite well.

author: baldengineer
author_rank: Contributor
timestamp: August 26, 2017, 12:11:30 am
content: Quote from: tautech on August 24, 2017, 07:40:19 am"New" is relative. Since it is the first major innovation in digital scope triggering in 30-40 years, I would still consider something from 6-7 years ago, "new."And since I've been out of the scope business for almost 6, my view of time scales is a bit skewed.