Background: I'm trying to build an AC coupled pre-amplifier that doesn't succumb to voltage offsets and input bias currents. The input signal has noise ~10 nV level, and I want a factor of a million in gain.
After studying the art of electronics, I'm trying to wrap my head around what are the problems input offset voltage can do, and how it can be circumvented.
Question: Will the following circuit need not worry about the V+ voltage offsets since it's AC coupled anyways?
My reasoning is that the 500k resistor lets the signal float on whatever voltage offset is there, i.e., there is no need to worry about error at 0V input.
The Circuit:
Best Answer
Your circuit will amplify the offset voltage by 100,000.
The 500K resistor adds an offset of Ib * 400K for zero offset current. The bias current is typically 1.2nA so it will contribute a temperature-sensitive 48V of output offset typically.
Note that 10nV of RMS noise is not achievable with this part. Also, if you want gain of 1,000,000 your bandwidth will be < 1Hz.