Pot on "-" terminal of OPA

[wuchy143]

Hi All,

I ran across an op amp which I cannot figure out how it works. More precisely I do not know how the attached potentiometer effects the OPA. I was able to do some simple calculations to get the DC gain and verified it in LTspice. Though, this doesn't help me in understanding what the pot does or how it is commonly used like this with an OPA.

Does anyone know or can explain what's going on?

 

[carbonzit]

Looks like it sets the input offset voltage (between V+ and V-), though I'm not sure why you'd want to do that: generally that's done by a fixed voltage divider. Perhaps it's a precision multi-turn pot to precisely set the balance point.

 

[crutschow]

It's to adjust the output DC offset to exactly 0V or whatever DC level you may want.