Compact Two-Stage Class-AB CMOS OTA for Low-Voltage Filtering Applications

Abstract

A compact OTA suitable for low-voltage active-RC and MOSFET-C filters is presented. The input stage of the OTA utilises the resistive tail-biased differential amplifier and the output stage relies upon the feed-forward class AB technique with common-mode rejection capability that incurs no penalty on transconductance/bias-current efficiency. Analysis on the achievable peak voltage swing of the OTA when employed in filters is given. Simulation results of a 0.5-V 100-kHz elliptic 5th-order filter based on the OTA's in a 2-V 0.18μm CMOS process indicate the differential peak voltage as large as 0.42 Vp (84% of the supply voltage) at 1% THD with the SFDR of 60 dB and the total power consumption of 50 μW.