DSO Samplerates - From when they´re "enough" and why?

[Martin72]

Elder siglent scopes got equivalent samplerate, the newer ones not.

https://int.siglent.com/products-overview/sds1000cfl/


Tek doc:

https://www.tek.com/en/documents/application-note/real-time-versus-equivalent-time-sampling

[David Hess]

As far as what sample rate is sufficient, it depends on the rise/fall time of the signal.  As a rough conversion, use the 0.35 rule to get MHz and then base sample rate on that.  So for example 100 nanoseconds is 3.5 MHz and the sample rate should be several times higher than that.

I am used to DSOs which support equivalent time sampling where the sample rate ends up being orders of magnitude higher than strictly necessary, so I almost never need to consider it.  I have never really considered a sample rate of 2.5 times to be sufficient.

But I believe most scopes, including Lecroy scopes, do some sort of peak detect when they resample data for display?

I think LeCroy's older DSOs were descendants of the transient digitizers they made for physics experiments, including nuclear weapons testing, so they had big sample memories and relied on post processing rather than processing during decimation where peak detection is done.  So for a long time, LeCroy eschewed peak detection.

I think the first "modern" DSO with peak detection was the Tektronix 2230 which was first available in 1986.  It has a 100 MHz bandwidth and 20 MS/s sampling to support peak detection down to 100 nanoseconds.  It was quickly replaced by the 2232 with a sample rate of 100 MS/s and peak detection down to 10 nanoseconds.  Both supported equivalent time sampling at 2 GS/s.

[2N3055]

My opinion(s) changed on that matter....

So the question is how many samples you like to have on a Rise/Fall edge... 5 or 10 or 20 samples?

At the end of the day, some Ferrari DSO is required as having RIS (LeCroy) on repetitive signal or than TEK for none repetitive.

I do not now know, how the new LeCroy has the repetitive signal limitation as using RIS.

On Siglent 2K+ did not found any RIS functions or I am missing something or may newer once as HD 2K or ??

It was repeated many times, when in dot mode it behaves as RIS...

[nctnico]

My opinion(s) changed on that matter....

So the question is how many samples you like to have on a Rise/Fall edge... 5 or 10 or 20 samples?

At the end of the day, some Ferrari DSO is required as having RIS (LeCroy) on repetitive signal or than TEK for none repetitive.

I do not now know, how the new LeCroy has the repetitive signal limitation as using RIS.

On Siglent 2K+ did not found any RIS functions or I am missing something or may newer once as HD 2K or ??

It was repeated many times, when in dot mode it behaves as RIS...

Not by design. If your signal is an exact multiple of the oscilloscope's sampling frequency, you won't get a signal on screen. The key to RIS / equivalent time sampling is that the sampling points are shifted in time so the signal is sampled at different points in time to make sure that you always get something on screen.

[David Hess]

Not by design. If your signal is an exact multiple of the oscilloscope's sampling frequency, you won't get a signal on screen. The key to RIS / equivalent time sampling is that the sampling points are shifted in time so the signal is sampled at different points in time to make sure that you always get something on screen.

The only time I have had that be a problem is when using the DSO to sample a signal from the inside of the DSO itself.

Some DSOs, and I know HP did this, randomly dither the sample clock and then measure the resulting sample time to avoid synchronization with the signal source.