High-swing folded cascode having a novel gain-boost amplifier

摘要

A circuit topology for gain boosted high-swing folded cascode has been improved to maximize the available dynamic range in applications having low supply voltage requirements. The circuit includes an improved gain boost amplifier that maximizes the available dynamic range for applications having low supply voltage requirements. The improved gain boosting amplifier includes a differential pair of input transistors connected to a current mirror, wherein a pair of current sources supply current to each lead of the current mirror. One lead of the current mirror is level-shifted by a transistor coupled to another current source, wherein the coupling of the transistor and the current source form the output of the amplifier. Effectively, the amplifier consists of an effective level shift and a series common-drain, common-gate amplifier. A reduction in transconductance g_m from the series combination is compensated by a current mirror ratio (K:1) between the level shift and the common-drain, common-gate amplifier. Specifically, the size of one of the transistors in the differential pair is a multiple integer (K) times the size of the other transistor in the differential pair. In addition, the size of one of the transistors in the current mirror is a multiple integer (K) times the size of the other transistor in the current mirror. Moreover the amount of current supplied by the second current source is a multiple integer (K) times the amount of current provided by the first current source.