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?
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.
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?