RAIL-TO-RAIL INPUT STAGES WITH CONSTANT GM AND CONSTANT COMMON-MODE OUTPUT CURRENTS

摘要

A rail-to-rail input stage with constant gm and constant common-mode output currents is provided. The common-mode output currents are controlled by the use of current switches. When low and high common-mode input voltages are applied to the input stage, the current switches take part of the tail currents of the input stage transistors, divides it into two equal parts, and directs the two equal current signals to the outputs. When intermediate common-mode input voltages are applied, the current switches regulate the tail currents of the input pairs such that the common-mode output current and gm remains constant. The current switches are responsive to changes in the common-mode input voltages, and thereby maintain the gm constant.