differential amplifier

[majerio]

i would like to know the factors that limit the amplifier common mode input range and the output range?
if both ac input are zero why the common mode gain is not zero?

 

[LvW]

.............
if both ac input are zero why the common mode gain is not zero?

The common mode gain does not depend on any input conditions. It is just a property of the circuit.

 

[checkmate]

What's the difference between the case when the absolute values on the inputs are 1V/1V and 2V/2V?
Both are dc inputs. The difference is in the common-mode!

The limitations can be summarized in that all transistors in the opamp must operate in the saturation region!
Or to be specific, the input/output ranges must satisfy all headroom requirements in the opamp.

The details are that it depends on opamp topology, and needs to be evaluated on a case by case basis.

 

[majerio]

The common mode gain does not depend on any input conditions. It is just a property of the circuit.

the ideal common mode gain is zero, what factor that make it nonzero