How this technique increase amplifier linearity?

I have seen this kinf of amplfier.

There are two resistors at source of input pair, how they improve the linearity of the amplifier?

any related paper?

thanks

Answer can be found on common analog IC textbook (please find attached)
Emitter degeneration allows an input signal level up to N*VT in linear mode at expense of voltage gain.
I hope it can help.
Mazz

The source resistors act as feedback to the mosfets by sampling current and feeding back voltage to the source of the transistor. This will decrease the gain (in this case, the transconductance of the transistors) and will linearize the gain (if the resistors are more linear than the transconductance of the transistor, which is usually the case, and are properly sized in relation to the transconductance of the transistors).

If Gm1 is the transconductance without the resistor, R is the resistor value, then the resulting transconductance will be Gm1/(1+Gm1*R).

As long as 1/Gm1 < R, the transconductance will be close to 1/R, and will be roughly independant of Gm1, so nonlinearities in Gm1 will not produce significant nonlinearities in the effective transconductance (and, thus gain...)