Design of 2-stage subthreshold opamp

[krithi]

Hi,

I am designing a 2-stage opamp (OTA) with n-channel input differential pair. This opamp is supposed to dissipate low power( 200nW)
My question is:
1) Only input differential pair transistors operate in subthreshold region and the other transistors operate in saturation region right?
2)How can input differential pair transistor be designed? what equation should be used?
3) Can u please tell me the name of the text book or any online reference material which walks me through the design of every transistor?

Thanks