Amplifier with rail-to-rail input capability and controlled transconductance.

摘要

@ A differential amplifier operable between a pair of supply voltages that define a rail-to-rail supply range contains a pair of differential portions (20 and 22) that together provide representative signal amplification across the supply range, although neither differential portion individually does so. A current control (24) regulates operating currents (IN and Ip) for the differential portions in such a way that the amplifier transconductance can be controlled in a desired manner as the common-mode part (VCM) of the amplifier input signal (VI+ and VI-) varies across the supply range. The transconductance is typically controlled to be largely constant. A summing circuit (26) selectively combines intemal currents (IA, IB, IC, and ID) from the differential portions to generate at least one output signal (IO+ and IO-) representative of the input signal.