A differential amplifier design and bias control technique of particular applicability for low voltage operation in which the threshold voltage of n-channel differential input transistors is controlled using substrate bias in order to allow a wider range of input signal levels. Further disclosed is a technique for controlling the substrate bias of the input transistors of a differential amplifier based on the level of the output of the amplifier in addition to a differential amplifier circuit capable of low voltage operation in which an additional bias current is introduced that enables the output pull-up current to be increased without increasing the pull-down current, as well as circuitry for optimizing the performance of the differential in both DDR-I and DDR-II operational modes.