I'm trying to understand how a differential amplifier rejects common mode noise and amplifies the differential/normal mode noise.
For that I use the following circuit topology and simulation:
When Vin+ and Vin- are differential Vout increases as follows:
When Vin+ and Vin- are same Vout doesn't move much as below:
In case of common mode inputs, the increase in Vout is less than the increase in Vin. So common mode voltages get attenuated or we can say the gain is negative.
In case of differential inputs however, the increase in Vout is much more than the increase in Vin. So differential mode voltages are amplified. Hence means positive gain.
I can see these as a result in simulations.
But I don't know what causes this logically. I mean current source is causing all of these but how? Why common mode inputs cause almost no difference in Vout but differential mode voltages have big gain? Is there a way to tell what is going on in this circuit in transistor level by a step by step manner to explain why are the results are like these?