A rail-to-rail amplifier input stage with ±0.35%g m fluctuation.

Abstract

A new scheme for achieving rail-to-rail input to an amplifier is introduced. Constant is obtained by using tunable level shifters and a single differential pair. Feedback circuitry con- trols the level shifters in a manner that fixes the common-mode input of the differential pair, resulting in consistent and stable oper- ation for rail-to-rail inputs. As the new technique avoids using com- plimentary input differential pairs, this method overcomes prob- lems such as common-mode rejection ratio and gain-bandwidth product degradation that exist in many other designs. The circuit was fabricated in 0.5- m process. The resulting differential pair had a constant transconductance that varied by only 0.35 for rail-to-rail input common-mode levels. The input common-mode range extended well past the supply levels of 1.5 V, resulting in only 1 fluctuation in for input common modes from to 2V.