How to define the input common-mode voltage for OTA? Thanks

[frozenduck]

ota dc input

When we design and simulate a fully differential OTA in open-loop, we just assign a DC value in the input volatge source to make sure the input transistors are in saturation region. Run AC, DC, etc. simulation.

For transition simulation in C-C feedback close-loop, these capacitors block the DC voltages. For the input, only AC signal can pass trough the capacitor and then go into the OTA.

How can we define the DC voltage at the input of OTA?
We should have a DC there to bias the input transistors, right? How to do that?

Thanks.

 

[ieropsaltic]

common mode voltage

You can apply the DC to the input transistor gates using a large resistor. The DC voltage itself can ba achieved from a stable reference as a bandgap reference.

This is almost similar to AC coupling for the input signal.