Two-Stage Feedforward 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 NMOS pseudo-differential amplifier with PMOS active load. The output stage relies upon the dual-mode feed-forward class-AB technique (based on an inverter-type transconductor) with common-mode rejection capability that incurs no penalty on transconductance/bias-current efficiency. Simulation results of a 0.5-V 100-kHz 5th-order Chebyshev filter based on the proposed OTA in a 0.18μm CMOS process indicate SNR and SFDR of 68 dB and 63 dB (at 50 kHz + 55 kHz) respectively. The filter consumes total power consumption of 60μW.