A Fourth-Order Tunable Bandwidth Gm-C Filter for ECG Detection Achieving −7.9 dBV IIP3 Under a 0.5 V Supply

This article introduces a fourth-order $G_{m}$ -C low-pass filter for ECG detection that achieves high linearity despite operating under a 0.5 V supply by 1) placing the differential pairs (DPs) of the employed $G_{m}$ stages in a two-loop feedback structure, 2) employing body-driven rather than gate-driven $G_{m}$ DPs, and 3) using current mirrors in place of cascoded transistors in a conventional $G_{m}$ stage. Measurement results of a $0.18~\mu $ m CMOS prototype show that the proposed filter, operating with a $V_{\text {DD}}$ of 0.5 V, achieves an third-order harmonic distortion (HD3) below −40 dB for input amplitudes up to 340 mV_pp. With an integrated noise of $154.7~\mu $ V_rms over a 240-Hz bandwidth, the filter exhibits a dynamic range (DR) of 53.6 dB, which is competitive with previously reported works.