how to design a high gain, bandwith, swing out opam!

I am designing a opam with 70-80db gain, and more than 20MHz bandwidth, and real-to-real output.

Can some one give me some suggestions about the structures?

THANKS
GDHP

if u r designing with cmos u can go with two stage op amp.

two stage? the first is the cascode and the second is the output stage. the first is the gain stage, and the second is the driving stage???

is it correct?

yes, i'm designing opamp using two stage structure as well. i manage to get 75dB open loop gain. however this is without compensation capasitor (I'm still learning on compensation technique). using 1.8V supply, it is really hard to implement cascode connection at differential stage. i dont really know how to get large bandwidth using two stage configuration.

what is your input swing? ie - do you need a rail to rail input stage, or just one diff pair?

hi, 70-80db gain and 20M bandwidth are easy to obtain, the popular structure is first folded-cascode or telescopic and second common source or class AB rail-to rail output stage.If you designed opamp is fully differential output ,maybe you need two stage cmfb.The compensation network is not complicated too,conventional series res and cap miller compensation or cascode compensation works.The latter will offer larger UGF,so i like to use cascode compensation.But it requires more larger gm than input differential pairs',this is difficuit to achieve under some conditions.
If you also want obtain rail-to-rail input common voltage range,you must use Complementary input stage,in this situation,the constant-Gm techniques must be adopted to insure the phase margin and non-linearity distortion.

good luck! regards

for 20mhz bandwidth u can go for two stage opamp

Two stage opamp is enough. What's your technology?

Rail to rail is difficult, I think you should Class AB structure