Low-voltage PVT-insensitive bulk-driven OTA with enhanced DC gain in 65-nm CMOS process

Abstract

This paper presents a high DC gain bulk-driven operational transconductance amplifier (OTA) for low voltage applications. A cross-coupled active load is employed at the bulk-driven input stage to enhance the gain of OTA. A cross-forward (CF) gain stage was placed between the input and output stages of the OTA to enhance the output stage transconductance. The CF stage improves the phase margin of OTA and keeps the amplifier stable even for large capacitive loads (up to 50 pF) and also improves overall DC gain. The proposed OTA simulated using UMC 65-nm standard CMOS process, operates at a supply voltage of 0.5 V. Simulation results show that the OTA provides a gain of 72 dB at very low-frequencies. It has a phase margin of 74° and a unity gain frequency of 680 kHz for a load capacitance of 20 pF. Because of the bulk-driven input stage, the OTA achieved rail-to-rail input common-mode range. When the OTA simulated with a supply voltage of 0.35 V and load capacitance of 20 pF, the OTA provides a DC gain of 55 dB and a phase margin of 68° at a unity gain frequency of 617 kHz. The power dissipations were 3.03 μW and 1.56 μW for supply voltages of 0.5 V and 0.35 V, respectively. In comparison to previous works, the figure of merit of the proposed OTA has more than doubled in all respects.