For simulation purposes, I know that one can setup a difference amplifier configuration and compensate for offsets for DC current by adding a voltage source on the inverting input, and adjusting it's value until output voltage is zero.
I tried the same thing for AC current, but it doesn't work. The offset is reduced a little bit, but it doesn't go below ~20uV RMS.
Basically I want to output a very small AC voltage from the differential amplifier, in the range of microvolts. Unfortunately, at that range the offset dominates the output.
How does one achieve 0V offset for AC current?
Best Answer
Trivial solution: coupling capacitor on output. This assuming the DC offsets aren't so bad as to cause clipping when the AC signal is overimposed.
If you have more sophisticated needs like preserving high CMR (unclear from the question if you do), then read http://www.ti.com/lit/an/sboa003/sboa003.pdf
If you have high-level DC bias on the input, then removing it before amplification is preferable:
This is the simplest idea, using a passive network; the two coupling capacitors allow only AC in, roughly speaking. More accurately they (together with the resistors) form high-pass filters. More sophisticated solutions are in the aforementioned TI app-note.