A Fourth-Order Tunable Bandwidth <i>G_m </i>-C Filter for ECG Detection Achieving −7.9 dBV IIP3 Under a 0.5 V Supply

This article introduces a fourth-order <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G_{m}$</tex-math> </inline-formula>-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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G_{m}$</tex-math> </inline-formula> stages in a two-loop feedback structure, 2) employing body-driven rather than gate-driven <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G_{m}$</tex-math> </inline-formula> DPs, and 3) using current mirrors in place of cascoded transistors in a conventional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G_{m}$</tex-math> </inline-formula> stage. Measurement results of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18~\mu $</tex-math> </inline-formula>m CMOS prototype show that the proposed filter, operating with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {DD}}$</tex-math> </inline-formula> of 0.5 V, achieves an third-order harmonic distortion (HD3) below −40 dB for input amplitudes up to 340 mV<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub>. With an integrated noise of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$154.7~\mu $</tex-math> </inline-formula>V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> over a 240-Hz bandwidth, the filter exhibits a dynamic range (DR) of 53.6 dB, which is competitive with previously reported works.