A high power efficiency Class AB switched-opamp for low voltage low power sigma-delta modulators
Two-stage Class-A switched-opamp (SO) is the most popular module in previous low voltage low power SO sigma-delta modulators (SDM). The SO saves about 30%∼40% of the total power since its output stage is just turned off at the integrating phase. To further increase efficiency a novel high power efficiency class AB current mirror SO is proposed in this paper. By turning off the entire SO together with its common mode feedback (CMFB) circuit, the power consumption of the SO can be reduced by 50%. A Class-AB load-compensated opamp version improves the power efficiency further. The proposed SO was fabricated in a 0.35µm TSMC CMOS standard process and achieved a DC gain of 62.7dB, a GBW of 4.39MHz and a slew rate of 1.2V/µs when the load capacitor is 10pF. The effective power consumption including the CMFB circuit is 6.6µW under 1.5V supply voltage. The simulation results showed that the proposed SO can be applied to low power low voltage SDM with a frequency of less than 0.5MHz.