Rail-to-Rail Operational Amplifier

[Micka999]

Hello everyone,
I’m doing project on topic rail-to-rail Op Amp, my task is to explain how each part of the circuit works. I have encountered rail-to-rail op amps and know some techniques for gm constant. But I can’t find anywhere on the internet a situation for this type of gm-constant biasing case. Can anyone explain to me which gm-constant biasing circuit it is, I know it’s a self-biased wide swing current mirror in input stage which represent constant current for polarization diff amp, but I can’t understand how gm-constant is realized.

Thanks all on your replys.