chopping frequency usage
Some preliminaries:
1. If the opamp have some mV offset and the diff-stage act as a gm-cell you have a differential switched current.
2. If you crossswitch these differential current in synchronism with the input voltage switch to an output current mirror the offset of the mirror does not get chopped out!
Because of 2. you need after the differential current switch a less offset contributing component. For instance an active PMOS load with high Vdsat and big area or a poly resistor.
Because of 1. the differential current should be filtered by a big cap. Then the dominant pole is set by this cap. Setting another cap as dominant is overkill.
From this cap voltage you need only a low voltage gain to the gate drive of the PTAT current sources.
The next spin of circuit desgin excellence is a AC-amplifier which detect the differential current, amplifies to a good level, synchron demodulate, filter and feed back to the differential input stage so to minimize the offset current ripple. That is the chopper noise regulator.
Have fun!