How to bais the error-amp in the Bandgap circuit?

[benchen]

voltage divieder bais

The error -amp in the Bandgap needs the biasing current or voltage, I wonder how to get it? If we use the PAPT current of the bandgap as the biasing current, there is a new problem which is how to start up this error amplifier?

 

[JT]

I find it pretty hard to apply self biasing and still have a
-stable bandgap circuit
-good start up behavior

It can be done, but I prefer simple resistor + current mirror biasing,
plain and simple, and it always works.

 

[qslazio]

for the error amp, We always use self-biased structure(etc. vgs/R or simple dioded voltage divider).
I think the best structure for the amp is simple current mirror load diff-pair with a cascode output stage. And the compensation is made inside the amp.

anyone has ideas about it?

 

[jiangwp]

benchen:

you are right.
The PTAT current which consists of BandGap that can be used to bias the erro amplifier.

I think the sequence is :

PTAT is ready, then erro amplifier is working normally after biases is ready by feedback.

Maybe, the response speed is not so fast. But, generally, it is enough.

There is not any problem.

I have taped out a chip like this structure.

 

[benchen]

Use simple voltage divider to bias the amp is Ok, but I found the PSRR is poor. Using the PTAT to bias the error ampilfier, the circuit is hard to start up correctly. jiangwap, can you show me an example of this circuit?