i would appreciate any ideas on how to increase the icm range of my opamp. The range seems to be linear only in a small segment of the rail to rail voltage. i.e i need 0.5 to 2.5V of icmr but come up with 0 to 1.5 Volts. (i am using a pmos input pair and 0 to 3Volts rail)
For a typical PMOS differential pair, the maximum input linear range can be from 0V to Vcc-Vds-Vthp.
If you are looking for up to 2.5V linear range, first ask yourself if it is possible to make (Vds + Vthp) < 0.5V over PVT corners. If it can not, you will need rail to rail structure.