LOW VOLTAGE HIGH PERFORMANCE CMOS OPERATIONAL AMPLIFIER WITH RAIL-

In this paper a low voltage constant transconductance (gm) rail-to-rail input and output CMOS operational amplifier is presented. The rail-to-rail common mode input range is achieved by using an n-channel and a p-channel differential pair connected in parallel. The constant-gm is achieved by using additional input differential pairs which control the tail current of the input differential pairs dynamically. The floating class AB control circuit is shifted to summing circuit, which results in a noise and offset of the amplifier. A floating current source biases the summing circuit and the class AB controls. This floating current source has the same architecture as the class AB control and provides a constant quiescent current, independent of the power supply. Special attention has been given to reduce the systematic offset voltage. Gain boost amplifiers are connected to provide not only an increase of the low frequency open loop gain but also a significant reduction of the offset voltage. Frequency compensation is performed by Cascoded Miller technique. The proposed opamp provides an open loop gain of 95.7 dB and a unity gain frequency (UGF) of 2.39 MHz