A 0.47mW 6th-order 20MHz active filter using highly power-efficient Opamp

This paper presents an ultra-low power 6^th-order 7MHz-to-20MHz tunable active-RC low-pass filter. Due to the proposed highly power-efficient Opamp, the filter only consumes 0.47 mA power from 1.8 V supply voltage, corresponding to 3.86 pW/Hz/pole normalized power. The Opamp utilizes an adaptive-biased pole-cancellation push-pull buffer to greatly reduce the power consumption. An adaptive bias circuit is proposed to cooperate with the Opamp to tolerate the PVT variations. The filter achieves 20.9 dBm in-band IIP3, and 298 μVrms integrated input-referred noise. The chip is fabricated in a standard 0.18 μm CMOS process, and occupies 0.21 mm² silicon area without ESD/pads.