8 GHz Sampling Oscilloscope 8 GHz BW - up to 1 TS/s ET Sampling - Page 1
Forum section: electronics / testgear

author: Free_WiFi
author_rank: Regular Contributor
timestamp: December 04, 2019, 07:49:19 pm
content: https://hackaday.io/project/167292-8-ghz-sampling-oscilloscope

author: jaromir
author_rank: Unknown
timestamp: December 04, 2019, 09:29:46 pm
content: While interesting topic, there are other two forum threads about it.https://www.eevblog.com/forum/testgear/ted-yapo-towards-an-open-source-multi-ghz-sampling-oscilloscope/https://www.eevblog.com/forum/chat/ted-yapo-towards-an-open-source-multi-ghz-sampling-oscilloscope-218878/

author: Marco
author_rank: Super Contributor
timestamp: December 05, 2019, 04:25:00 pm
content: Calling these comparator based devices samplers is inaccurate IMO. They have much slower acquisition than true samplers and are kind of boring.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: December 05, 2019, 05:44:51 pm
content: SyntheSys Research used a similar technique in their BertScopes.A set of fast comparators with DACs driving the set points and accurate gating delays for the latching.You can then sweep the contours of the eye diagram as well as quickly establishing a bit error rate.SyntheSys Research got bought by Tektronix, who extended the product line, with the fastest BertScope covering 28.6 Gbps.Nowadays you can get real time scopes that are fast enough to do the same thing.

author: FriedLogic
author_rank: Regular Contributor
timestamp: December 07, 2019, 07:31:13 pm
content: Quote from: Marco on December 05, 2019, 04:25:00 pmBut are there any readily available, not too expensive, and reasonably easy to implement 'real' samplers around?

author: nctnico
author_rank: Super Contributor
timestamp: December 07, 2019, 08:06:33 pm
content: Quote from: Marco on December 05, 2019, 04:25:00 pmNo, the term 'sampler' is correct. You don't need to sample a repetitive signal with a samplerate which is higher than the Nyquist frequency.

author: Marco
author_rank: Super Contributor
timestamp: December 07, 2019, 09:18:12 pm
content: They aren't sampling though, they are comparing. They use a gated comparator, not a sampling gate.

author: David Hess
author_rank: Super Contributor
timestamp: December 08, 2019, 01:35:58 am
content: Quote from: nctnico on December 07, 2019, 08:06:33 pmA sampler convolves the sampling gate with the input signal which in the ideal case produces a non-linear sin(x)/x frequency response which is why the 0.35 rule does not apply. This explains the discrepancies he noted in his presentation. The sin(x)/x frequency response also means that you can completely characterize the non-linear frequency response of a sampler by measuring its first null.In contrast a comparator input stage is linear which produces some other limitations that a true sampler does not have. Comparators for instance have limited input full power bandwidth.Still considering the cost of the comparator method, he gets very good results. But having seen the sampling breadboard he made, I am not surprised he only got poor performance with it. He was right about the contrast between the complex engineering design yet simple construction; you really do need to know what is going on and see the physical circuit in a non-straightforward way.I suspect part of his problem with his analog sampler experiment was confusing sequential and random sampling. He described random sampling but built something suitable only for sequential sampling or at least it looked that way. The two have very different circuit requirements.

author: Marco
author_rank: Super Contributor
timestamp: December 08, 2019, 08:01:21 am
content: With a proper sampling gate you can also get away with having an inaccurate sampling time base. Just sample a low passed clock signal from a crystal, both during triggering and at the same time as sampling ... the samples from the clock will give you an accurate time, even if the timing of the sample pulse was not very accurate. This should allow you to get away with simply discharging a capacitor to determine the timing of the sample pulse, which would usually be too sensitive to temperature for long timespans.

author: David Hess
author_rank: Super Contributor
timestamp: December 09, 2019, 02:34:09 am
content: That is how aninphase and quadrature phase sinewave sampling time delay counterworks. They are commonly used where high sample rates are required. Some very fast frequency counters use that method and it would also be suitable for a digital storage oscilloscope that supports a high waveform acquisition rate.Older digital sampling oscilloscopes did not bother because the avalanche pulse generator which produces the sampling gate could not operate fast enough to require it.

author: Fungus
author_rank: Super Contributor
timestamp: December 09, 2019, 07:28:55 am
content: Quote from: nctnico on December 07, 2019, 08:06:33 pmOr even a non-repetitive signal.The devil is in the phrase "Nyquist frequency". A single rising edge can easily break your Nyquist frequency.

author: tggzzz
author_rank: Super Contributor
timestamp: December 09, 2019, 09:13:47 am
content: Quote from: nctnico on December 07, 2019, 08:06:33 pmThe term sample is indeed correct.Nyquist's frequency isalwaysvalid, but you need to understand the definition of "signal bandwidth". If you don't understand that then Tayloe mixers (commonly found in cheap SDR dongles) will seem to be impossible magic.