differential amplifier ac response

[shibinpv]

Can any one tell ,why ac gain varies in differential amplifier with resistive load while varying the ac input voltage? ( means getting high gain for low input voltage and low gain for higher ac input voltage)

 

[LvW]

I think you are in error. How and where did you observe something like this???
AC response is ALWAYS a small signal characteristic of an amplifier.
That means, for a transfer curve which is not 100% linear (and which does not exist in reality) the gain is calculated/measured on the basis of very small amplitudes.
For larger input amplitudes the output amplitudes are not growing in proportion to the input - but this must not be considered as a gain reduction, because distortions are created leading to an output waveform which is not sinusoidal anymore.
In this case you are not allowed to define any gain by dividing the non-sinusoidal output by the sinusoidal input.