A global operational amplifier with constant-gm input and output stage

The principle and design of a 3 V two-stage CMOS operational amplifier are described. A rail-to-rail input stage shows almost constant transconductance independent of the common mode input voltage range with global transistor operation region. This new technique does not make use of accurate current-voltage relations of MOS transistors. Hence it can be applicable to a simple linear relationship of currents. The proposed global two-stage op-amp also can operate both in strong inversion and in weak inversion. Class AB output stage proposed also has a full output voltage swing and a well-defined quiescent current that does not depend on power supply voltage.