Harmonic Error Cancellation for Accurate Square-wave-based Bio-Impedance Measurements
Harmonic Error Cancellation for Accurate Square-wave-based Bio-Impedance Measurements
复制标题
谐波误差消除，用于基于方波的精确生物阻抗测量
DOI：
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
S. Ha
中科院分区：
文献类型：
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作者：
S. Subhan;S. Ha
生物阻抗谱测量组织在一定频率范围内的阻抗，已被广泛用于提供监测人体健康的关键信息。其传统方法使用正弦波电流刺激组织和正弦波解调所得电压，提供了精确的阻抗测量，但涉及庞大的组件和功率效率低下，由于正弦波形生成和模拟信号乘法。相反，使用方波时钟的方法可以具有更大的面积和功率效率，但是由于方波中存在谐波，因此固有地在测量结果中具有相当大的误差。在本文中，我们提出了一种技术，以消除所造成的方波激励和解调的谐波的误差。该技术基于方波的所有谐波的幅度比已知的事实，通过将基于方波的高次谐波测量结果减去或添加到基波输出作为简单的后处理计算来抵消谐波误差。使用通用电极和组织模型的仿真结果表明，该技术可以提供生物阻抗的精确测量，仅考虑五个频率倍数，幅度误差<0.5%，相位误差< 0.2。由于该方法不涉及正弦信号生成和模拟混合，因此足以以低面积和功率开销集成在可穿戴健康监测设备中。
Bio-impedance spectroscopy, which measures impedance of the tissue over a frequency range, has been widely used to provide crucial information for monitoring human health. Its conventional methods using sine wave current stimulation of the tissue and sine wave demodulation of the resultant voltage provide an accurate impedance measurement, but involve bulky components and power inefficiency due to sinusoidal waveform generation and analog signal multiplication. Instead, the method using square wave clocks can be much more area and power efficient, but inherently has substantial errors in the measured result due to the presence of harmonics in square waves. In this paper we propose a technique to cancel the errors caused by harmonics of the square wave stimulation and demodulation. The technique, based on the fact that the magnitude ratio of all the harmonics of a square wave are known, cancels out harmonic errors by subtracting or adding the square-wave-based measured results at higher harmonics to the fundamental output as a simple post-processing calculation. Simulation results using a generic electrode and tissue model show that this technique can provide a precise measurement of the bio-impedance with <0.5% magnitude error and < 0.2 phase error considering just five frequency multiples. Because this method does not involve sinusoidal signal generation and analog mixing, it is adequate to be integrated in a wearable health monitoring device at low area and power overhead.