Inverting analog signal about its offset

[pavjayt]

To invert an analog signal about its offset, using an opamp with a gain of -1 and offset adjustment is the only way to achieve this or are there any new chips that do that for you these days? There is always some uncertainity in the offset adjustment with respect to the amplitude of the input signal and I need it to be as accurate as it can be at any amplitude levels.

thanks

 

[MikeMl]

Sounds like you need an accurate voltage reference for the opamp's offset adjustment. Circuits that use a pot tied to a supply voltage are only as good as the voltage regulation of the supply. If the supply changes 10%, so does the offset.

If you use a precision voltage reference IC to derive the offset, you can get stability approaching 0.01%...

 

[MrAl]

Hi,

I dont think there is any way to do this automatically. That's because the 'chip' would never know if your signal was riding on some offset or just changing very slowly.

If the offset is constant i would think you should have no problem using an op amp. If the offset changes dynamically over time, then you've got to decide what time constant to use anyway.

One way to get this action somewhat automatically is with a sample and hold where you sample for the offset during known quiet periods.

 

[pavjayt]

I did this in a normal (using POT) way to adjust the inverted signal's offset on a breadboard and worked fine at that time. Now I want to integrate it into my existing design where the user already adjusts the offset of a signal that is fed into another circuit. I would like to keep the user adjust to only one pot, but at the same time output an inverted signal about the offset of the above signal. How can we achieve this other than using another pot.

One way I can see is by inverting the offset bias using an unity gain op-amp that the user is adjusting already and feed that into the inverted signal. Are there better designs than this or this should be good.