Bias current for Opamp in bandgap

[microtronics7]

Hi,

I am a novice analog designer. I am going to design an opamp for bandgap application in 130nm technology. My opamp should have
High gain
good bandwidth
low offset
low power. Maximum on current is 5uA for entire bandgap
I have chosen two stage miller opamp.

1. How shall i choose my bias current for the diff pair? Once i know i would keep overdrive of 5% of Vdd as Dr. Baker says and size accordingly.
But how to choose the current? Is 500nA a good choice?

 

[keith1200rs]

https://www.edaboard.com/threads/241728/

Keith

 

[microtronics7]

But I want the rules to be followed for bias current selection during op amp design. Is 500nA a good option?

 

[penance]

I don't think two stage miller opamp is a good choice，you can try folded cascode opamp

 

[microtronics7]

But in most band gap design they use 2 stage miller opamp. What is the adv of folded cascode over two stage milleer?

 

[microtronics7]

Can anyone suggest me an opamp architecture where Vdd noise appears at the O/P. I am in need of such architecture....

 

[leehying]

Hi,
With only 5uA current, I believe your bandgap wont drive large RES/CAP load.
So either two stage miller opamp or folded cascode opamp should be OK
Come on! Design it first.