deba wrote on Dec 17th, 2016, 7:04am:Hi,
In a multi-pole and zero system, the relation between GBW and settling is not very well defined. Even if the GBW is high, due to non-monotonic phase droop, the settling may take a long time.
The criteria of moving the auxiliary loop dynamics beyond the GBW of the overall loop is just a safe criteria for stability. w4 > w5,w6 will try to maintain the first order behaviour of the overall loop.
It will help to show the opamp/circuit which you are working.
this is the op-amp circuit from the Bult and Geelen paper. The main stage is a folded cascode amplifier. the 2 folded cascode with pmos input transistors are the auxiliary amplifiers. The current sources are also realized as cascoded structures with additional gain.