What is the usage of the PMOS FET in this simple amplifier?

[Davidy]

This is a simple amplifier in a typical bandgap circuit.

Who can tell me why there is a PMOS FET "ST1" in the middle of the circuit?

what is the useage of it?
Thanks!

 

[Verba]

I think it's negative FB at DC
It keeps the current through P49 constant.
And it helps to charge NLL, NLR capacitance

 

[lastdance]

Re: What is the usage of the PMOS FET in this simple amplif

when in+/- exceeds input common mode, this PFET turns on to pull VOUT low.

Added after 25 seconds:

when in+/- exceeds input common mode, this PFET turns on to pull VOUT low.