In this paper, a second-order tunable low-frequency low-pass filter (LPF) dedicated to bioimpedance spectroscopy is proposed and designed in a 0.18 <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$\mu m$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mi>m</mi> </mrow> </math></EquationSource> </InlineEquation> CMOS process with 1.8 V supply voltage. The filter consists of low-<InlineEquation ID="IEq2"> <EquationSource Format="TEX">$G_m$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>G</mi> <mi>m</mi> </msub> </math></EquationSource> </InlineEquation> operational transconductance amplifiers (OTAs) based on the super-source follower differential pair with source degeneration. Current division and cancellation are applied to the output stage in order to reduce the equivalent <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$G_m$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>G</mi> <mi>m</mi> </msub> </math></EquationSource> </InlineEquation>. By adjusting the division factor through a control circuit, the transconductance can be tuned from 23.1 to 775 nS. Measurement results show that the cut-off frequency of the proposed filter can be tuned from 794 Hz to 2.9 kHz, with less than 1.5 <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$\mu W$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mi>W</mi> </mrow> </math></EquationSource> </InlineEquation> power consumption. Measurements verify the linearity of the filter, exhibiting a total harmonic distortion (THD) lower than –41.9 dB with a 250 <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$mV_{pp}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <msub> <mi>V</mi> <mrow> <mi mathvariant="italic">pp</mi> </mrow> </msub> </mrow> </math></EquationSource> </InlineEquation> signal at 100 Hz. The circuit also achieves a dynamic range of 43.8 dB and a DC gain error below 1 dB.

A 2nd-Order Tunable Gm-C Low-Pass Filter for Bioimpedance Spectroscopy

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发表日期：

2026年3月22日

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Erick Iván Barros de la Cruz,
Juan David Salazar Cardona,
María Teresa Sanz-Pascual

摘要

In this paper, a second-order tunable low-frequency low-pass filter (LPF) dedicated to bioimpedance spectroscopy is proposed and designed in a 0.18 $\mu m$ $μ m$ CMOS process with 1.8 V supply voltage. The filter consists of low- $G_m$ $G_{m}$ operational transconductance amplifiers (OTAs) based on the super-source follower differential pair with source degeneration. Current division and cancellation are applied to the output stage in order to reduce the equivalent $G_m$ $G_{m}$ . By adjusting the division factor through a control circuit, the transconductance can be tuned from 23.1 to 775 nS. Measurement results show that the cut-off frequency of the proposed filter can be tuned from 794 Hz to 2.9 kHz, with less than 1.5 $\mu W$ $μ W$ power consumption. Measurements verify the linearity of the filter, exhibiting a total harmonic distortion (THD) lower than –41.9 dB with a 250 $mV_{pp}$ $m V_{pp}$ signal at 100 Hz. The circuit also achieves a dynamic range of 43.8 dB and a DC gain error below 1 dB.