Hi!

Sorry for late reply.

If you have the schematic, please tell what the problem is? Why you do not simulate?

Hi Abhishek,

I am assuming you have picked up this two stage diff amp schematic from some Analog Design book, and now you need help on how to size each and every transistor ? Possibly, you would also like to know which simulations to perform and how to perform them.

Before proceeding with design steps and understanding how to size each and every transistor you need to know specifications for your two stage diff amp. To name a few, differential gain, common mode gain, output swing, unity gain bandwidth, PSRR, slew rate , current consumption/power requirement. Having these specifications help you in sizing each transistor. Also, I strongly recommend, you have a clear understanding of which transistor influences which specification of your diff amp.

For instance, you differential gain is dependent on gm of your input differential pair etc.

If you have your specifications then mention them, or we can assume some arbitrary (yet realistic) specification for your diff amp and then proceed.

Also, I don't know for which type of simulation you have setup your testbench but I can see that you have AC component at only negative input. You need to have that at both the inputs for an AC simulation to measure gain (what most people look for when designing an amplifier).

-Clark.