Voltage divider for a square wave

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am85

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Hi,

I am reading a high voltage square wave using an ADC. Firstly, I have a voltage divider using a 500k ohm resistor on every line coming from the wave generator and a 1.5k ohm resistor between both lines. Then comes the programmable amplifier and the ADC. I get the following plot :

Is this the correct signal i should get? If yes then why is the upper part of the wave a bit tilted and not straight anymore? and is it ok that the edges are round now? how to reduce those effects?
when I exchange the inputs to my circuit I get the following plot, which plot is the correct one ?


Thanks a lot in advance.
 

Your waveforms look exactly like those when an oscilloscope probe's compensating capacitor is not set to the "correct" value.

Here's a brief writeup on this --
https://www.ni.com/white-paper/4721/en

Without actually knowing your circuit setup, I suggest you connect in some small trimmer caps on your inputs, and adjust these for flat waveshapes - assuming your siggen is giving out a true square shape.

cheers!
 

Yes I have read about this compensation capacitors. One source suggested having capacitors in parallel to every resistor of the voltage divider, but it didn't work. So can u please explain a bit more where exactly i should connect these capacitors. I have the voltage divider built in the cable between the wave generator and my circuit. then my input circuit looks like this:


My voltage divider in the cable looks like this:



Thanks.
 


i doubt i will be able to tell you EXACTLY where to put in caps, since this depends on a detailed knowledge of your entire physical setup. Randomly putting in caps everywhere doesn't sound a very useful idea - you'd be just shooting in the dark & hoping that BY SOME CHANCE you hit the right combination. I don't think so.

However if you Google for "oscilloscope probe compensating cap" or similar, you will get a host of details on real theory & practise.

Here's just a few that i found
**broken link removed**
https://www.picotech.com/applications/how-to-tune-x10-oscilloscope-probes.html
**broken link removed**

If you go through a few of these & understand the theory, then with a little thought you should be able to solve YOUR specific problem.

cheers1
 

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