Re: rail to rail opamp
Rail to rail:
differential amplifier with NMOS, current source to the gnd
in parallel with
differential amplifier with PMOS, current source from Vdd
*NMOS diff does not work with small voltages, but PMOS diff can.
*PMOS diff does not work with high voltages, but NMOS diff can.
*In the middle both PMOS and NMOS amplifiers can work, but the gain is higher from previous two possibilities. Some sort of gm control should be added in order to compensate gm dependance from dc point.