1 V rail-to-rail constant-gm CMOS op amp

A 1 V rail-to-rail constant-gm CMOS operational amplifier is proposed. This study shows that keeping the sum of currents in the complementary differential pairs constant rather than controlling the tail currents produces a constant-gm input stage operating in the weak inversion. The currents in the n-channel differential pair are regulated to keep the sum of currents in the complementary differential pairs constant using a negative feedback loop. This study also provides experimental results obtained from a 0.35 m CMOS prototype chip.