Common-mode rejection ratio analysis of fully differential class AB two-stage op-amp with and without common-mode feedback circuit

A fully differential class AB two-stage op-amp with and without common-mode feedback circuit (CMFB) are proposed. There are 4 schematics to be proposed. The first schematic is CMOS complementary input with class AB output without CMFB circuit. The second schematic is CMOS complementary input with class AB output stage with CMFB circuit. For low voltage operation, the tail current source of the first and second schematic are removed. Half-circuit concept is used to analyse the DC differential mode gain and DC common-mode gain of both 2 schematics to compare for CMRR. Full analysis procedure are also used to derive for CMRR equation of the first schematic.