Two input stages (10,12) are interconnected so that their input common mode voltage ranges to one side of signal ground are combined to provide a common mode voltage range substantially equal to the supply voltage. One stage has N-channel differential input transistors (N1,N2), while the other stage...http://www.google.com/patents/US4554515?utm_source=gb-gplus-sharePatent US4554515 - CMOS Operational amplifier
