應用低通濾波器之電容式指紋感測研究

生物辨識的應用可以說是相當普遍，而指紋感測也是其中一種辨識方式，本論文提出一種可用於感測指紋的電容式陣列讀取電路，有別於過去的電容式指紋感測器，原理是透過低通濾波過度頻帶特性，改變其濾波器電容值來達成指紋感測，本電路設計採用TSMC 0.18μm 1P6M CMOS標準製程所實現。讀取電路包含有8×8個指紋感測像素單元，整體電路操作頻率為600MHz此頻率是由壓控震盪器產生0V~1.8V方波訊號，再經由峰值偵測器鎖住低通濾波中輸出之最高電位，但每2.7mv/f的電壓變化，難以判斷出正確電容值，所以透過減法放大器將感測電壓放大為每12mv/f，使電壓輸出範圍變大，達成指紋辨識。整體面積為852.0um × 650.92um，工作電壓為1.8V，感測電容範圍為0fF~60fF，輸出電壓範圍為0.4V~1.25V。關鍵字:電容式指紋感測器、低通濾波器、峰值偵測器

關鍵字

電容式指紋感測器；低通濾波器；峰值偵測器

並列摘要

The application of biometrics is quite common. And fingerprint sensing is one of the common identification methods. This paper proposes a capacitive array reading circuit for sensing fingerprints that different from the capacitive fingerprint sensor of the past. The principle is to achieve the output voltage change required for fingerprint sensing. By changing the capacitance value of the low-pass filter affect the characteristics of transition band. This circuit design is realized by TSMC 0.18μm 1P6M standard CMOS process. The reading circuit contains 8×8 fingerprint sensing pixel units. The overall circuit operating frequency is 600MHz that generated by a 0V~1.8V square wave voltage controlled oscillator. Use the peak detector to lock the highest potential output in the low-pass filter. However, every 2.7mv/f voltage change of the output waveform will make it difficult to determine the correct capacitance value. Therefore, a subtractive amplifier is used to amplify the sensing voltage to a change of every 12mv/f to increase the voltage output range to realize a fingerprint sensor. The chip area is 852.0um × 650.92um, works at 1.8V power supply, The sensing capacitance range is 0fF~60fF, The output voltage range is 0.4V~1.25V. Keywords: Capacitive Fingerprint Sensor, Low Pass Filter, Peak Detector Circuit,