Input/output rail-to-rail CMOS operational amplifier with shaped common-mode response
This paper presents an input/output rail-to-rail class-AB CMOS operational amplifier with reduced variations in unity-gain frequency over the entire voltage range. The rail-to-rail amplifier input stage is based on two parallel-connected complementary differential pairs. Variations in the small-signal response are kept to a minimum by realizing an adequate shaping of the CM response of the input stage, while still reducing deviations in the total limiting current of the two input pairs with respect to traditional solutions. This is achieved independently of the g(m)-I-D characteristic of the amplifier input devices and of any strict matching condition between the complementary input pairs. Experimental results from a 3-V 0.8-mum CMOS test-chip are given.
rail-to-rail cmos operational amplifiers constant-g(m) circuits