Hi,
I'm designing an op amp. Here's the spec.
GBW = 1G
power: <20mw, vin_cm =0.9v, input swing: 0.5v p-p, output swing: 1v p-p
I used folded cascode as my 1st stage and CS as the 2nd. The individual performance
is (before I combine them):
folded cascode: DC gain=27.95dB, GBW=2.92G, PM=71.4
CS : DC gain=26.78dB, GBW=12.27G, PM=85.1
However, the overall performance is poor. DC bias condition is correct. I got DC gain=48dB, GBW<=800MHz. Even if I use a large compensation CAP, the PM is still less than 15. Please give me some suggestion. Thanks in advance.