differential amplifier help

[hanhan]

Hi,
I am new and want to ask about differential amplifier.
Can you shed some light on the circuit below?
Why transistors M2 and M4 are added in the circuit?

I learnt some basic about differential amplifier but when I see this circuit, it is confusing me.
Why transistors M2 and M4 are added in the circuit?

 

[RCinFLA]

It is cascode current source structure (M2,M1 is mirrored to M3,M4). It makes the current source have higher impedance.

 

[RCinFLA]

Spoke too quickly, It is a mixer (multiplier). V1, V2 would be chopper for input signal Vb1.

 

[hanhan]

hi, i am not sure what you meant. This is a differential amplifier i saw in an old thread in this forum.