Question

difference between constant current bias and current mirror circuit

Answer 1

if the two pMOS are equal, they provide the same drain current to both the branches: suppose that Vbias is chosen so that the drain current will have a certain (constant) value Ibias. Moreover, if a new pMOS is added and connected at the same Vdd and with the same gate potential Vbias, it will generate the same drain current as M1 and M2.

But often the current mirror configuration is used:



where the drain current of M1 is Ibias (and it is the drain current of any other transistor equal to M1 and connected in the same way).

I think that the two configurations (with appropriate Ibias and Vbias values) are equivalent