Subthreshold op amp design

[bharath_k]

Hello Everyone,

I have a question regarding designing a op-amp is subthreshold region. I have found few papers which are really helpful but I am still not getting clear idea.

In the above circuit how to I design M3, M4 and M5? In op amps biased in saturation region we typically use ICMR+ and ICMR- values to obtain the device sizes. What parameters should I use in case of subthreshold region?

or I bias only M1, M2 and M6 in subthresold region and M3, M4, M5 and M7 in saturation region?

Thanks,
Bharath

 

[jjx]

(When you use the input common-mode range as spec, you mean that you use the "hand calculations" to reach the point where thy leave their saturation regions?)

Anyway, depends on your application, I would focus on the overall specification in terms of eg gain, bandwidth, phase margin, current consumption or what-have-you. Just push the transistors as far into subthreshold as you can while meeting the specification. You also know that S3=S4=kS6 and S5 = 2kS7 also in subthreshold. So not that many parameters to sweep.