I am designing an OPAMP with 0.6μm technology (Vtp=-0.9V, Vtn=0.7V) and i have a specification of ICMR=0.5-2.5V to meet. The power supply is 3V (single). I have considered the clasic 2 stage OPAMP with Miller compensation, the cascode and the folded cascode OPAMP, but i don't see how the ICMR requirement could be satisfied.

The folded cascode OPAMP seems to meet either the upper or the lower specification depending whether it has a NMOS or PMOS input differential pair, but not both. Could anyone suggest a simple topology that could meet the ICMR specification?

Thanks in advance.

Thanks for the advice. I have found some rail to rail topologies, but they are too complicated and might even not satisfy other requirements. I was wondering if there is some kind of trick to increase ICMR using a simple topology.

Dan, i tried both approaches: source followers work just fine until Vcm~0.8V but after that the gain is lowered and resistor dividers seem to degrade performance, especially slew rate. I guess it has something to do with input capacitances but still i cannot find any way around it.