Design of Capacitive Fingerprint Sensing Chip with Automatically Adjustable Dynamic Range

[[abstract]]本論文提出了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，指紋皮膚處在不同的乾、濕、髒污狀態時，將直接地影響電容式指紋感測器的擷取的輸出影像清晰度表現，故吾人提出一種具備有調整感測範圍區間功能的電容式指紋感測器，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4×128個指紋感測器像素單元，解析度為442dpi，整體電路的操作頻率為500KHz，電容的感測範圍為0fF~75fF，針對指紋表面不同的乾濕狀況會感應出不同的電容範圍，吾人所提出的電路會依據感測到電容的範圍大小自動調整感測器的感測範圍，以能得到最佳的電壓輸出範圍，讀取電路的輸出電壓範圍分別是：Mode1對應到較乾的指紋感應電容範圍(0~30F)，輸出電壓範圍為0.23V~1.75V；Mode2對應到一般的指紋感應電容範圍(15~50F)，輸出電壓範圍為0.23V~1.75V；以及Mode3對應到較濕的指紋感應電容範圍(35~70F)，輸出電壓範圍為0.27V~1.77V。晶片整體面積為0.330×7.996mm2，功率消耗為0.915mW。[[abstract]]A capacitive fingerprint sensing chip is proposed in this thesis with automatically adjustable output dynamic range for enhancing the quality of acquired image under various surface conditions of fingerprint. The presented chip is implemented with TSMC 0.18μm 1P6M standard CMOS process. The proposed fingerprint sensing chip is constructed with an array of 4 by 128 sensing units, and has an image resolution of 442dpi. The chip operates at 500KHz. The fingerprint induced capacitance to be sensed ranges from 0 to 75fF. The induced capacitance will be crowded to a smaller range according to the wetness/dryness condition of the fingerprint surface. A dry fingerprint will induce a lower capacitance value than normal fingerprint, while a wet one will induce a larger value. To get an optimal output dynamic range under various fingerprint surface condition, an automatically adjusting sensing scheme is implemented in the proposed chip. The measured output dynamic range is 0.23-1.75V for dry fingerprint with induced capacitance range of 0-30fF (Mode1). The measured output dynamic range is 0.23-1.75V for normal fingerprint with induced capacitance range of 15-50fF (Mode2). The measured output dynamic range is 0.27-1.77V for dry fingerprint with induced capacitance range of 35-70fF (Mode3). The chip area is 0.330 × 7.996mm2, and consumes 0.915mW.[[note]]碩