Two stage opamp differential feedback with different i/p and o/p common mode

[vlsi_design2]

Hi, I am designing a two stage differential amplifier with different i/p common mode voltage and o/p common mode voltage. When I connect it in closed loop using resistors R2 and R1 , dc current will flow due to difference in common mode. Is it ok for dc current to flow when the amplifier will be used in closed loop ? I want to characterise the closed loop response like step response etc.. Thanks

 

[andre_luis]

In the electronic world it is usual to describe circuits with schematics just to know what in the world you're talking about. Anyway, what about adding a buffer stage at the second stage output just to decouple output biaasing effects on the attenuation resistor divider?

 

[FvM]

In the first order, it's the resistive load by the feedback resistors that affects amplifier gain, not the dc output current. A two stage fully differential amplifier is surely far from an ideal amplifier, adding output buffers can be a step to improve it.