PAC simulation for PSRR

Hello,
I'm running PSS, PAC to determine the PSRR of a DAC.

Setting the vsin supply with PAC=1, do i need to set the amplitude and frequency? What difference does it make?

I tried both simulation with PAC=1, amplitude=50mV and frequecy=1/2fc
and simulation PAC=1, amplitude=0, frequency=0

there is a difference in PSRR reading. But I dont know the relationship. Can someone kindly help me on this.

Normally you should sweep your AC frequency-for instance- 1Hz to 100MHz in logarihtmic and look at the AC gain from your output to Vcc.Therefore psin component has to have an AC voltage level-for instance-1uV
then you can see AC gain in dB from your output and Vcc as PSRR..