1-V quasi constant-gm input/output rail-to-rail CMOS op-amp

A CMOS operational amplifier with input/output rail-to-rail range is presented. The circuit operates with a 1-V single supply. It uses dynamically biased input level shifters, controlled by a novel tuning scheme, to extend the input common-mode voltage range from one rail to the other. The tuning circuit takes the total biasing current of the amplifier input stage and, hence, its small-signal response into account. As a result, the total input transconductance variations are lower than 710% over the entire voltage range. Experimental results on a test-chip fabricated in standard 0.8-mm CMOS technology are given. r 2003 Elsevier B.V. All rights reserved.