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is it true, oscilloscope must reach at least 4x observed freq?
nctnico:
--- Quote from: oxy on September 12, 2022, 06:32:08 pm ---Lets take the example of the picoScope Series 6000E:
It has several models with bandwidths ranging between 500MHz and 1 GHz, yet all of them with sampling rate of 2.5Gs/s.
As I understand the sampling rate sets over Nyquist the max. frequency that I can observe. Thus what hardware specification differentiates those oscilloscopes on the bandwidth?
--- End quote ---
Likely they all have the same hardware but there is a software controlled filter in the input circuitry which limits the actual bandwidth. In some cases the lower bandwidth models have some extra filtering components in the input circuitry but the basic hardware design is the same.
bdunham7:
--- Quote from: oxy on September 12, 2022, 06:32:08 pm ---Lets take the example of the picoScope Series 6000E:
It has several models with bandwidths ranging between 500MHz and 1 GHz, yet all of them with sampling rate of 2.5Gs/s.
As I understand the sampling rate sets over Nyquist the max. frequency that I can observe. Thus what hardware specification differentiates those oscilloscopes on the bandwidth?
--- End quote ---
That is entirely unrelated to your initial question. As already mentioned, the bandwidth rating is typically designated as the frequency where the amplitude response is down -3dB or to about 70%. The high frequency roll off can be due to the bandwidth limitations of the analog inputs or it can be the result of something further up the line (software filter, etc).
tautech:
If as it seem sampling rate is what the thread is really about however 5x sampling vs BW is more the industry standard today.
This with a shared ADC design provides 2.5x BW sampling which comfortably meets Nyquist.
tggzzz:
--- Quote from: oxy on September 12, 2022, 06:32:08 pm ---Lets take the example of the picoScope Series 6000E:
It has several models with bandwidths ranging between 500MHz and 1 GHz, yet all of them with sampling rate of 2.5Gs/s.
As I understand the sampling rate sets over Nyquist the max. frequency that I can observe. Thus what hardware specification differentiates those oscilloscopes on the bandwidth?
Thanks for ur very nice inputs! :clap:
--- End quote ---
For digital signals the period is irrelevant; only rise time is important. For a little theory and some practical measurements, see https://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/
If you have a repetitive signal, the sampling frequency is separate to the signal frequency. I have a scope that measures 50ps rise times with ~40kSa/s. No, that does not violate Shannon/Nyquist! Various manufacturers have different names for the techniques, e.g. equivalent time sampling.
tggzzz:
--- Quote from: tautech on September 12, 2022, 08:28:49 pm ---If as it seem sampling rate is what the thread is really about however 5x sampling vs BW is more the industry standard today.
This with a shared ADC design provides 2.5x BW sampling which comfortably meets Nyquist.
--- End quote ---
So you think that to usefully observe a 1kHz digital signal, you only need a 5kHz scope? That's nonsense, as you well know.
The only thing that matters is the rise time. Digital circuits don't "care" when the next transition might occur, if ever.
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