應用於生醫訊號偵測之互補式金氧半八通道類比前端生理訊號截取電路

Abstract

1887 年，英國科學家 Augustus Waller第一次向世人發表了心電圖。1912 年，俄國生理學者 Vladimir Vladimirovich Pravdich-Neminsky 紀錄下腦部的電波訊號。而十九世紀末科學家也紀錄到了肌肉裡的電訊號並且發現這些訊號和許多神經上的疾病或身體上的活動息息相關。所以深入的研究這些生理訊號變成了重要的課題。由於生理訊號有低頻、低振幅且獨特等特性，所以訊號的放大、低雜訊且有可調性成為設計的一大挑戰。本論文即為實現一個可用於放大Electrocochleography (ECoG)、Electromyography (EMG) 和 Electrocardiography (ECG) 等多種生理訊號的類比前端放大器，並與一已設計好的十位元每秒五十萬次取樣差量調變逐次漸進式類比數位轉換器,整合成一類比前端系統。其中類比前端放大器,為了能夠同時觀察多個通道，本設計使用八通道架構，此類比前端放大器包含了低雜訊前端放大器、可程式增益放大器、八通道多功器和轉阻放大器。其中新架構低雜訊前級放大器可以防止電極造成的直流電壓偏移而飽和電路，高頻截止頻率可調於0.96K Hz到7.1K Hz，低頻截止頻率可低於1Hz，雜訊效率因子(NEF)為1.77，整個類比前端放大器增益為40.6-60.9dB，並有很高的線性度，功率消耗為53.1μW。整體類比前端的功率消耗為77.54μW,平均每個通道所消耗的功率為9.69μW，在台灣積體電路製造股份有限公司與國家晶片系統中心的幫助下，此類比前端電路晶片將以 0.18 微米製程實現。

This paper presents an 8-channel analog front-end (AFE) acquisition circuit for neural recording systems. It consists of an 8 channel analog front-end amplifier (AFEA) and full-integrated with a 500 KS/s 10b ADC. The AFEA consists 8 analog front-end blocks, an 8-to-1 multiplexer, a trans-impedance amplifier (TIA). Each of the analog blocks in AFEA is implemented a low-noise preamplifier and a programmable transconductance gain amplifier (PTGA). It is designed for amplification, filtering, and converting to digital signals of different kinds of biopotential signals, such as electrocorticogram (ECoG), electrocardiogram (ECG) and electromyogram (EMG). These biopotential signals have the characteristics of small amplitudes, low frequency and variability. The AFE acquisition circuit which is fabricated in TSMC 0.18μm CMOS process can adjust gain at three steps(40.6/48.7/60.9 dB) digitally, the high-pass corner can achieve as low as 0.69Hz and low-pass corner can be adjusted to three steps(0.96k/3.01k/7.1k Hz). The input-referred noise of the AFEA is 5.46μVrms. The noise efficiency factor is 1.77 of low-noise preamplifier. The whole AFE acquisition circuit power consumption is 77.54μW where 9.69μW per channel (6.71μW of AFEA per channel, and 2.98μW of ADC per channel ).