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Help me understand oscilloscope peak acquisition mode
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David Hess:

--- Quote from: 2N3055 on December 06, 2023, 06:48:16 pm ---On both RTB2000 and even more on Siglent SDS2000X+ (that has order of magnitude more memory), Peak mode is pretty much unnecessary.
--- End quote ---

That is going to depend on how the acquisition record is processed to produce the display record.  If the processing produces an analog like display, then a fast peak should be invisible despite being present in the data.  So peak detect mode could still be useful if it highlights the envelope of the signal.

Below is an example of peak detect mode on a Tektronix 2232, but it is identical on the 2230 which is the first DSO that I know of with peak detection.  The display is 50 points per horizontal division so 2ms/50 is 40us or 25 ksamples/second which is way too slow to detect the high frequency switching which would otherwise cause severe aliasing, but peak detection forces the maximum sample rate of 100 Msamples/second and then decimates to record the highest and lowest values which are *both* displayed during the sample interval.
alm:

--- Quote from: David Hess on December 07, 2023, 12:53:55 am ---That is going to depend on how the acquisition record is processed to produce the display record.  If the processing produces an analog like display, then a fast peak should be invisible despite being present in the data.  So peak detect mode could still be useful if it highlights the envelope of the signal.
--- End quote ---
I did tests a while ago, though I can't find the post right now, on a Lecroy WavePro 7300A. So MAUI, on which the current software for their X-Stream and MAUI light scopes are based. I used a pulse train with as low a duty cycle as I could generate with my pulse generator, and as long as the combination of memory depth and sweep speed were such that the sample rate stayed high enough to sample the pulses, the pulses would be displayed regardless of the zoom. Even if the pulse width was way below a pixel width at that zoom level. So at least those scopes appear to be doing some sort of envelope filter during downsampling.
David Hess:

--- Quote from: alm on December 07, 2023, 01:21:58 am ---I did tests a while ago, though I can't find the post right now, on a Lecroy WavePro 7300A. So MAUI, on which the current software for their X-Stream and MAUI light scopes are based. I used a pulse train with as low a duty cycle as I could generate with my pulse generator, and as long as the combination of memory depth and sweep speed were such that the sample rate stayed high enough to sample the pulses, the pulses would be displayed regardless of the zoom. Even if the pulse width was way below a pixel width at that zoom level. So at least those scopes appear to be doing some sort of envelope filter during downsampling.
--- End quote ---

I did the same thing on my 2230 and 2232 when I first got them, using a variable width pulse which could be smaller or larger than the sample interval.  These old DSOs lack a graded index display so they will always show a pulse at full brightness if it is recorded.

But if a more modern instrument produces a graded index display, then a narrow recorded peak will be too dim to view, like on an analog oscilloscope, unless the display record processing takes this into account.  I am not surprised that some DSOs do this even if it sacrifices display accuracy.
2N3055:

--- Quote from: David Hess on December 07, 2023, 05:23:05 am ---
--- Quote from: alm on December 07, 2023, 01:21:58 am ---I did tests a while ago, though I can't find the post right now, on a Lecroy WavePro 7300A. So MAUI, on which the current software for their X-Stream and MAUI light scopes are based. I used a pulse train with as low a duty cycle as I could generate with my pulse generator, and as long as the combination of memory depth and sweep speed were such that the sample rate stayed high enough to sample the pulses, the pulses would be displayed regardless of the zoom. Even if the pulse width was way below a pixel width at that zoom level. So at least those scopes appear to be doing some sort of envelope filter during downsampling.
--- End quote ---

I did the same thing on my 2230 and 2232 when I first got them, using a variable width pulse which could be smaller or larger than the sample interval.  These old DSOs lack a graded index display so they will always show a pulse at full brightness if it is recorded.

But if a more modern instrument produces a graded index display, then a narrow recorded peak will be too dim to view, like on an analog oscilloscope, unless the display record processing takes this into account.  I am not surprised that some DSOs do this even if it sacrifices display accuracy.

--- End quote ---

We spoke about this many times. It won't be too dim to view. Modern scopes produce "analog like" view. Pixel brightness is nonlinear, and there is a lowest value that it will go.
So basically, if you have only one repetition of sample in area you will still get, say, 30% of brightness.
Brightness (and color mapping in color mode) is not done from 0-100% in linear fashion.

When done right, this is superior how CRT works because it shows signals CRT wouldn't show but still convey repetition/density info..

David Hess:

--- Quote from: 2N3055 on December 07, 2023, 06:20:02 am ---We spoke about this many times. It won't be too dim to view. Modern scopes produce "analog like" view. Pixel brightness is nonlinear, and there is a lowest value that it will go.
So basically, if you have only one repetition of sample in area you will still get, say, 30% of brightness.
Brightness (and color mapping in color mode) is not done from 0-100% in linear fashion.

When done right, this is superior how CRT works because it shows signals CRT wouldn't show but still convey repetition/density info..
--- End quote ---

I think the most that can be said about graded index DSO response is that it is proportional in some way, which may or may not accurately convey repetition/density info.  This would have to be tested and nobody does, but it would be easy with a mark 1 eyeball tangential measurement.

The response of an analog CRT is not even close to linear; it is a power function, and it conveys quantitative repetition/density info very accurately.
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