I have a differential input Vin1 and Vin2 to PMOS P1 and P2. Vin2 is constact (1.5V) and have a capacitor (0.5pF) below transistor P2. ISS is 1uA and gm of Vin1 is about 5u. P2 is connected via switch and I want to control the gain by turning on the P2 for certain time. But I give time 1us gain is not as expected. I am taking the output in between P2 and capacitor. I expect gain to be (gm x time /C). What is wrong in my calculation.

 

You need to post a schematic of your circuit so we can understand what you are referring to.

 

thank you for the reply.

This the rough schematic I want to implement. where first discharge the cap Cs by turning on the phi1 and then charge for certain time by turning P2.

 

Sorry for bad English in my previous post. I want to know the Vo equation in terms of gm, time (P2 ON), capacitance and Vin, VR