transistors region of operation in 2-stage OpAmp

[Spliter]

I have 2-stage opamp with Miller compensation. I know that all transistors sholud be in saturation, but in which inversion should they work? Weak, strong inversion or something else?

 

[erikl]

Depends on quite a lot of specifications: gain, speed vs. power consumption, common mode voltage range, noise, ...

Read David M. Binkley's book: "Tradeoffs and Optimization in Analog CMOS Design", especially chap. 5: "Design of CMOS Operational Transconductance Amplifiers Optimized for DC, Balanced, and AC Performance", which describes 2 different OTA topologies each of them working in either weak, moderate, or strong inversion operation, thus resulting in OTA structures of different specifications regarding the a.m. properties.

 

[Spliter]

Ok, thanks, but I olnly need to know do all transistors should be in same operating mode (like "all are in strong inversion") or in various aplications, for example, differential, input transistors are in weak inversion, and output transistors are in moderate inversion?

 

[lamoun]

You can use different "modes" for the transistors. There is no need all of them to operate in the same region.