可拉伸式感測電極與非晶氧化銦鎵鋅薄膜電晶體差分放大電路之整合於心電訊號量測之應用

Abstract

本研究目標為開發應用於心電訊號量測之可撓性電子元件，共設計兩種不同的可拉伸式乾式電極，皆以聚二甲基矽氧烷做為基底材料，並分別使用銀及奈米銀線作為感測電極。導線的部分特別設計彎曲的結構，使得電極貼片與皮膚能夠服貼，進而提高訊號雜訊比。兩者之表現與使用市售銀/氯化銀(Ag/AgCl)電極之量測結果相近。 接著於聚醯亞胺基板上製作可撓性差分放大電路，其由八個非晶氧化銦鎵鋅薄膜電晶體組成(放大倍率約3.5 V/V)。其中四個薄膜電晶體組成主動式負載NMOS差分放大器，而另外四個薄膜電晶體組成雙輸入轉單輸出電路。電路之差模增益約為3.5 V/V，共模增益約為0.6 V/V，共模抑制比約為15.3 dB。 最後，將電極貼片與感測電路整合於心電圖訊號量測。先利用可拉伸式乾式電極接收皮膚上的訊號，再透過可撓性非晶氧化銦鎵鋅薄膜電晶體之前端差分放大電路進行初步放大(放大倍率約3.5 V/V)，而後利用自組之後段濾波電路(放大倍率約101 V/V，頻寬為0.4 ~ 48 Hz、 60 Hz帶拒)進行雜訊濾除，從而於示波器上擷取ECG波形。所得心電訊號之QRS平均波峰約為85.73 mV，雜訊約為22.21 mV，得訊雜比值約為11.73 dB。

In this research, developing flexible electronic devices for Electrocardiogram (ECG) measurement is demonstrated. First of all, two types of stretchable dry electrodes are designed, both of which are based on Polydimethylsiloxane (PDMS), and the electrodes use silver (Ag) and silver nanowires (AgNW) respectively. It’s worth mentioning that the design of matrix networks makes the patches conformably adhere to the skin surface, so that the signal-to-noise ratio can be improved. Both of their performance are similar to the measurement results using commercial silver/silver chloride (Ag/AgCl) reference electrodes. Next, the flexible differential amplifier circuit which is composed of eight amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs) is fabricated on polyimide substrate. Four of them act as a differential pair, and the other form a differential to single ended converter. The differential mode gain of the circuit is about 3.5 V/V, and the common mode gain is about 0.6 V/V, so the common mode rejection ratio (CMRR) is about 15.3 dB. Finally, the patches and circuit are integrated into ECG measurement. The ECG signal is received from the skin surface by three pairs of stretchable dry electrodes, and then the signal will be amplified by a-IGZO TFT based differential amplifier circuit (gain is about 3.5 V/V). After that, the breadboard filter circuit (gain is about 101 V/V, and bandwidth is 0.4 ~ 48 Hz 60 Hz notch) is used for noise filtering, so as to monitor the ECG waveform on the oscilloscope. The average peak of the QRS wave obtained is about 85.73 mV, the noise is about 22.21 mV, and the signal-to-noise ratio is about 11.73 dB.