Common-mode rejection ratio analysis of rail-rail input stage fully differential two-stage OP-AMP

A fully differential rail-rail input stage and class AB output stage with and without common-mode feedback circuit are proposed. There are at least 4 schematics to be proposed. The first schematic is CMOS rail-rail input stage and class AB output stage without common-mode feedback (CMFB) circuit. The second schematic is CMOS rail-rail input stage and class AB output stage with CMFB circuit. For low voltage operation, the tail current sources of the first and second schematics are removed. As a consequence, there is no voltage drop between drain and source terminals of the current source, and bulk-source voltage effect of the input transistor is removed.