Key result
A fourth-order lowpass filter based on the proposed biquad circuit consumed 4.26-nW static power from a 0.9-V supply with a 100-Hz cutoff frequency, outperforming previous nanopower filters.
The proposed CMOS biquad filter achieves state-of-the-art low power consumption and supply voltage for electrocardiography readout systems.
May enable nanowatt ECG monitoring in wearables; leaves open clinical validation before adoption.
This paper develops a compact power-efficient CMOS buffer to operate as a nanopower lowpass biquadratic cell. Unlike other recently reported CMOS biquads with passband gains that are attenuated by the bulk effect, this biquad attains a near 0-dB passband gain without gain compensation. It acquires the same levels of input and output common-mode voltages making it useful for cascade realization of a higher order lowpass filter. To demonstrate the potential application of the proposed biquad, a fourth-order lowpass filter was designed based on the proposed biquad circuit and fabricated in the 0.35-μm CMOS process to serve electrocardiography readout systems. Measurement results show that the filter consumes 4.26-nW static power from a 0.9-V supply providing a 100-Hz cutoff frequency. The prototype chip occupies a silicon area of 0.11 mm2and contributes an input-referred noise of 80.5 μVrms. For a 60-Hz input frequency associated with -50-dB third-order harmonic distortion, a dynamic range of 48.2 dB is achieved. The lowest power supply rejection ratio of 40 dB was obtained at 100 Hz. Compared with the previous state-of-the-art designs in the category of nanopower filters, the proposed filter consumes the least power from the lowest supply voltage.
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Thanapitak et al. (2018) studied this question. CMOS buffer-based biquadratic cell vs. previous state-of-the-art designs was evaluated on Power consumption and cutoff frequency. A fourth-order lowpass filter based on the proposed biquad circuit consumed 4.26-nW static power from a 0.9-V supply with a 100-Hz cutoff frequency, outperforming previous nanopower filters.
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