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Siglent SDS 1202X-E sampling anomaly?

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MacMan72:
I figured it out… I think. First, I couldn’t zoom in as close as I thought I needed to because the waveform is 3v pk-pk and I ran into the vertical zoom limits at about 100mV/div. That’s what prompted me to stop scanning and zoom further in since it will let me zoom further on a saved waveform. I had initially tried to zoom in on the top of the waveform to look at overshoot but when I tried to zoom horizontally, the waveform sloped away (since the rise time of the calibration signal sucks  (first image) (properly captured) (you’re welcome). So I switched to the bottom of the waveform to see what that looked like. That’s when the weird digital effect became apparent. When I look at a similar waveform generated by my AWFG, it has a nice fast rise time and typical overshoot with settling ripple like I was expecting (Second and third images). So, looking at the lower portion of the waveform, I was zooming all the way in and, here’s the point finally, so close, I’m looking at individual datapoints and it seems as though the Instek is doing a polynomial fit between the points to maintain continuity while the Siglent is just playing connect the dots. At least it does that for Normal mode. Averaging looks to be employing a curve fit method similar to the Instek.

tautech:

--- Quote from: MacMan72 on July 25, 2023, 01:49:33 am ---I’m looking at individual datapoints and it seems as though the Instek is doing a polynomial fit between the points to maintain continuity while the Siglent is just playing connect the dots. At least it does that for Normal mode.

--- End quote ---
Not quite.
Siglent scopes have 2 display modes, interpolated (joined dots) or Dot mode.

In Dot mode when Stopped you can clearly see the individual datapoint dots especially when zoomed in.
In Run and Dot mode, the trigger rate overlays the acquisitions so to look like an interpolated trace, however it is not.

Some even keep their DSO's in Dot mode but might switch to interpolated in a capture to see the trace better.
Keep exploring.  ;)

MacMan72:
That's what I'm saying... the Siglent is doing linear interpolation in Normal Aquisition mode and a polynomial fit (with more data points, I'm assuming from multiple sweeps determined by the Average # set by the user) in Average Aquisition mode. If you look at the images, the first is normal with dots, the second is normal with vectors (straight linear interpolation between datapoints). The third is dots with averaging, the fourth is averaging with vectors (polynomial fit).

tautech:
If this worries you and rather than looking at these quite sensitive DSO's, instead investigate presence of any local RFI.

I have had customers call and question noise on the traces and working against their disbelief had them find a horrible noisy wallwart across the room behind a curtain was the real issue.

Probing technique, ditching the probe reference (GND) lead in favor of the spring in the probe accessories does markedly reduce the antenna effects of the reference lead.

Martin72:

--- Quote ---Probing technique, ditching the probe reference (GND) lead in favor of the spring in the probe accessories does markedly reduce the antenna effects of the reference lead.
--- End quote ---

See also this picture with no gnd connected, gnd connect via the normal lead/clip and gnd connected via the spring.

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