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Siglent SDG1020 square signal "dirty"

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Xyphro:
Hi!

Did anybody ever have a close look at the Siglent SDG1020 square wave output at low frequencies?

Settings: 1 Hz, Square, 50% duty. Zoom in to the rising or falling edges. Output 1 (right BNC connector).

Looks like a bug in the DDS section (see attached picture).

Output 2 is free of this problem.
Other waveforms look fine at Output 1...

It could be a feature which is useful at sine wave output, but useless and nasty for square wave output: Dithering of the phase accumulator for low frequencies?!?

Best regards,

Kai

rf-loop:
It have discussed also earlier.

Your image do not look like 50% duty.
Out from 50% this situation is more bad than 50%.

It is not DDS problem and/or FW problem at all.

Square wave is special case.  It is derived from internal sinewave using PECL comparators. (and this principle is not only Siglent special)
 This make square wave function different as all other functions.

On some HW's PECL comparator hysteresis setting is not optimum and in some cases hysteresis setting resistor value  change may give some amount better result.

Of course there may be some other problem in some individual unit if this signal pathway to comparator is noisy (example some component failure what is related to this signal noise)
Now if use low frequency and specially other than 50% duty this small noise may lead to wrong comparator "switch" specially if comparator hysteresis window is too narrow.

It is explained littlebit more here.

And here.
If need better signal quality specially for low frequencies  it is better to use pulse than square.

Xyphro:
tak, rf-loop!

I just also noticed, that the pulse mode is clean and was wondering why.

bmwnomad:
Is this the same thing you guys are talking about? 

I have an SDG1025 and was going to send it back under warranty for a replacement, but if they are all like that then maybe I'll have to live with it.

Attached are scope snapshots.  Yellow are channel 1, 1khz square wave and blue is channel 2, 1khz square wave.  I set it on infinite persistance for a few seconds to show the glitches.

Channel 2 is fine, as is channel 1 pulsed output(not shown), it's just channel 1 square wave that looks like crap.

Steve

rf-loop:
This difference between channels is now strange.

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