Performance improvement of operational amplifier in subthreshold region using forward body bias

Abstract

In this paper, the effects of applying the forward body bias technique to an operational amplifier with transistors operating in the subthreshold regime are reported. A previously established operational amplifier is chosen as a reference and is realized in Cadence Virtuoso. The forward body bias technique is then applied to different transistors in the circuit, and the effects are studied. Consequently, an intelligent method for applying forward body bias is developed, through identification of the critical transistors and calculation of the optimum body bias for each transistor. Through application of the proposed methodology to the given circuit, the gain of the operational amplifier increases by 42 percent and the integrated input noise decreases by 2 percent, with negligible increase in power consumption. The final operational amplifier realized has a gain of 80.79dB, integrated input noise (0.01Hz–200kHz) of 23.67µV, a unity gain bandwidth of 152.96kHz and a power consumption of 322.54nW. The simulations are carried out at a supply voltage of 0.5V, using the Spectre simulator of the Analog Design Environment.