two-stage op amp hand calculations and parameters

in doing the hand calculations for designing a two-stage op amp, what equations should i use? there are lot of equations that i tried but it doesnt seem to workout -_-

and what common values of parameters should I use in doing the hand calculations in getting the W/L ratio?

assuming you are doing compensation with common source second stage then

A= gm1 rout1 * gm2*rout2
w_3db = 1/(rout1*(Cout1+ gm2*rout2*Cc)
w_unity = gm1/Cc
w_2 = gm2/Cout
w_zero = gm2/Cc

where the rout1 are the usually rop//ron and Cc is the compensation cap.

Once you figure out what gain you want and what gm to use then you can figure out the W/L from there using your judgement of what bias current to use and what overdrive you want.

the relative tradeoff between bias current and your overdrive is determined by input/output swing range, slew rate, noise performance, etc.

If you are using deep sub-micron process，then you cant count on the equations from almost all the textbooks you have learnt to get the accurate W/L ratio.Just run simulation and rely on the intuition you have learnt from those equations.

Hello

in the analog design you must pass the hand calculation, even these and specially for the deep submicron will be far from what you calculate, nevertheless it will be in the same direction, if you dont understand the hand calculation then you will not know how to modify your circuit when you simulate it. in addition the hand calculated values will put you nearer to the solution but not the exact. the different is coming from the fact that during the hand calculation we are dealing with very simplifies equation while in the simulator the model is more complicated and includes much more factors that we doesnt take with our calculation.

the first thing in the design is to choose the minimum length which is equal to at least 2*minimum technology length to reduce the channel length modulation and enhance the circuit impedance and gain.

for your case of two stage op-amp I would highly recommend you to use the book of CMOS analog circuit design by Allen and Holberg, in chapter 6 he gave a complete procedure not only for the two stages but for other types as well op-amp topologies.

read that chapter and if you didnt understand it you can message me or post here