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Siglent SDS1104X-E anomaly on what should be a simple task.

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py-bb:

--- Quote from: tautech on December 27, 2022, 06:45:19 am ---
--- Quote from: py-bb on December 27, 2022, 04:27:06 am ---
One issue I've found with the DSO scopes around me (whether it generalises I can't say) is that if you use a voltage offset they get bad.

--- End quote ---
See Offset Range (Probe 1X) P8 in Datasheet:
https://int.siglent.com/u_file/document/SDS1000X-E_DataSheet_EN04D.pdf

Yep show us some screenshots.

--- End quote ---

I've literally just put that away. I've got an older LeCroy to hand I'll take screenshots in a bit. I've not tried the DC offset thing before, but I have tried adjusting the offset, the more extreme the offset the slower the rise time on the square wave is - this is just "panning" around on the calibrate hook.

It's an extreme effect and I do wonder how it works to generate it, I imagined it'd generate a voltage and feed that into an op-amp, that's what makes me think saturation could be in play.

py-bb:

--- Quote from: tautech on December 27, 2022, 06:45:19 am ---
--- Quote from: py-bb on December 27, 2022, 04:27:06 am ---
One issue I've found with the DSO scopes around me (whether it generalises I can't say) is that if you use a voltage offset they get bad.

--- End quote ---
See Offset Range (Probe 1X) P8 in Datasheet:
https://int.siglent.com/u_file/document/SDS1000X-E_DataSheet_EN04D.pdf

Yep show us some screenshots.

--- End quote ---

Okay it wasn't with the calibration port. I was using a function generator (but not changing the output just "panning" the waveform) - will definitely do it just to figure out what it's called, but not now sorry. Either in the next hour or two or tomorrow.

Performa01:
The topic of overload recovery pops up over and over again, and still doesn't seem to be understood by everyone (for instance it has nothing to do with semiconductor switching times or something like this) and it certainly can't be a deal breaker.

I've tried to explain the issue several times, the last one was reply #41 here:

https://www.eevblog.com/forum/testgear/rtb2004-still-worth-it-in-2021/msg3788153/#msg3788153

What I would like to add: A higher input offset compensation range in these split path input buffers will also result in worse input overload recovery beaviour.
 

py-bb:
Okay I did the experiment.

First up the full wave we're viewing. There is a 50 ohm terminator in play (as with the DC offset the scope kept overloading and tripping)



As you can see not a bad square, the rise is pretty good.



Okay now we view the top - hmm... that wasn't there before.



In this picture I've added a positive DC offset which the square wave is on top of, as a result the square wave's amplitude is lower, as you can see - it's a lot less bad.

It's a pretty bad artifact. According to the service manual it's just a DC bias into an op-amp.

Great that those attachments didn't work when it did it that way.

BTW this is an extreme example, I had it at 6.84v offset (maxes out at 10) so it's not "terribly far" and a frighteningly large artifact but when viewing something riding on an offset that's nearby it's OK, so as long as the signal's "within view" it tends to be good.

There's a person here saying "oh that's expected behaviour" https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-anomaly-on-what-should-be-a-simple-task/?action=dlattach;attach=1167288;image - this image is not. That's terrible! I agree with OP here and is on screen!

You need to trust the scope to reproduce a signal that fits in the range accurately, there's no excuse for that!

2N3055:

--- Quote from: py-bb on December 28, 2022, 11:58:25 am ---Okay I did the experiment.

First up the full wave we're viewing. There is a 50 ohm terminator in play (as with the DC offset the scope kept overloading and tripping)

(Attachment Link)

As you can see not a bad square, the rise is pretty good.

(Attachment Link)

Okay now we view the top - hmm... that wasn't there before.

(Attachment Link)

In this picture I've added a positive DC offset which the square wave is on top of, as a result the square wave's amplitude is lower, as you can see - it's a lot less bad.

It's a pretty bad artifact. According to the service manual it's just a DC bias into an op-amp.

Great that those attachments didn't work when it did it that way.

BTW this is an extreme example, I had it at 6.84v offset (maxes out at 10) so it's not "terribly far" and a frighteningly large artifact but when viewing something riding on an offset that's nearby it's OK, so as long as the signal's "within view" it tends to be good.

There's a person here saying "oh that's expected behaviour" https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-anomaly-on-what-should-be-a-simple-task/?action=dlattach;attach=1167288;image - this image is not. That's terrible! I agree with OP here and is on screen!

You need to trust the scope to reproduce a signal that fits in the range accurately, there's no excuse for that!

--- End quote ---

Do you plan to actually read what people answered and explained to you?

You are overloading scope input amplifiers by several order of magnitude. Distortion you see is caused by user insisting on doing what people are telling you is wrong.

ALL of your signal has to be on screen. If you have 100 mV P-P riding on top of 10V DC offset, you can set scope to 20mv/div, set offset for 10V (if scope has that offset in that range) and nicely see signal on the screen.
Because setting offset subtracted 10V DC component form the signal and you defacto have a 100mV P-P signal left for scope to analyse.

If you put in 10V P-P into scope set to 20mv/div and use scope offset to look at top level of signal, you are shoveling 10V signal in preamp set for 800mV full range... You get overdrive....

So in short, ifm when you are setting the scope, some part of signal goes under or over visible screen, you are doing it wrong.... signal has to enter the screen from the left, and exit to the right and never go outside top or bottom. It actually can, 10-20% more but that is it...

Once you accept that, I am willing to explain why is it so. And yes, all current digital scopes,cheapest to very expensive,  from all brands do this same very thing.

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