1-V rail-to-rail constant trans-conductance operation amplifier

A 1-V rail-to-rail operational amplifier with a constant gain is presented in this paper. A feedback structure which provides the availability of using two differential pairs is employed to maintain the trans-conductance constant in the input stage. Moreover, the feedback-control trans-conductance circuit enhances the robustness of the operational amplifier since it needn´t consider the matching of differential pairs, and it also widens the common input voltage which makes the power supply voltage to be at 1 V possible. Considering the low supply voltage and enough capability to drive large loads, a feedback class-AB structure is available in the output stage. With the supply voltage at 1 V(loaded by 5 pF and 10 KOmega), the operational amplifier is simulated by HSPICE in the standard 0.18 mum CMOS process, achieving a low-frequency voltage gain of 76 dB, a unit frequency bandwidth of 5.2 MHz and phase margin of 63deg, with a power dissipation of only 95 uW.