Simple Scheme for the Implementation of Low Voltage Fully Differential Amplifiers without Output Common-Mode Feedback Network

A simple scheme to implement class AB low-voltage fully differential amplifiers that do not require an output common-mode feedback network (CMFN) is introduced. It has a rail to rail output signal swing and high rejection of common-mode input signals. It operates in strong inversion with ±300 mV supplies in a 180 nm CMOS process. It uses an auxiliary amplifier that minimizes supply requirements by setting the op-amp input terminals very close to one of the rails and also serves as a common-mode feedback network to generate complementary output signals. The scheme is verified with simulation results of an amplifier that consumes 25 µW, has a gain-bandwidth product (GBW) of 16.1 MHz, slew rate (SR) of 8.4 V/µs, the small signal figure of merit (FOMSS) of 6.49 MHz*pF/µW, the large signal figure of merit (FOMLS) of 3.39 V/µs*pF/µW, and current efficiency (CE) of 2.03 in strong inversion, with a 10 pF load capacitance.