Single Stage Differential Amplifier AC, Tran graph

[Rohbinhoodie]

Okay so, I could set all the mosfets Saturation and get 29dB voltage gain in tran analysis.
But I have some questions.

1. AC(left one) and tran(right one) analysis in this circuit, they have different voltage gain. In Tran Analysis I could get 29dB voltage gain(Upper ones are output nodes, below ones are inputs),
But in AC analysis I'm not even sure if I got a correct gain graph for the circuit. Can someone tell me why? isn't it correct that I should get same gain in AC analysis and Tran analysis?

2. In DC analysis, I swept input voltage from 0 to 2.5v bcus Vdd is 2.5v and I could get this output voltage graph. But the output voltage was just a horizontal line.
Is my DC analysis in this circuit correct? Can someone pls tell me?

I use Hspice prgoram
Mosfet model is TSMC 180nm
I set the length as 0.3um
I set the Iss 0.2m

+Vdd = 2.5v
+0.18um < Length < 5um
+0.18um < width < 100um
+Vcm = 1.25v

 

[BigBoss]

Your AC graph does not show the Gain. You should define AC Gain or compare Input and Output values in dB scale by frequency. AC gain is defined as ;
20*log[mag(Vout)/mag(Vin)] and X axis will be the swept frequency. Phase vs. frequency should also be observed.