Design of Capacitive Fingerprint Sensing Chip with Dynamic Range Selection Scheme

[[abstract]]生物辨識是近年來最熱門的研究議題，而其中最可靠的就是採用指紋辨識。電容式指紋感測器的原理，是藉由量測感測電極板與指紋表面紋路的深淺距離不同，而造成的電容值變化，以此擷取出指紋影像。 在本論文中，我們將會討論具動態範圍選擇之電容式指紋感測晶片之研製。藉由感測器單元電路佈局安排方法，可以消除寄生電容的影響，，並且採用最小尺寸的MOS開關以減少MOS開關的非理想效應，透過感測架構開關切換達成三種不同的輸出範圍，利用類比至數位轉換器將三種輸出範圍做相加，以獲得良好的電容對電壓轉換特性。而功率消耗方面，則透過控制感測讀取電路中緩衝放大器的靜態消耗電流，以節省功率消耗。 我們採用國家晶片系統設計中心提供的UMC 0.18μm Mixed-Signal 1P6M CMOS製程，完成16乘16陣列的指紋感測器晶片實作，包含了感測器陣列和周邊控制電路，以及類比至數位轉換器。 晶片工作電壓為1.8V，時脈速度為4MHz。感測電容範圍為0fF至65fF，對應的類比輸出電壓為1.3V至0.2V，以及六位元的數位輸出。[[abstract]]In recent years, Biometric Identification has become the most popular research topic, and one of the most robust methods is fingerprint identification. A capacitive fingerprint sensor acquires the fingerprint image by measuring capacitance variation, caused by different distance between sensing electrode and fingerprint surface. In this thesis, we present a capacitive fingerprint sensor readout circuit with a dynamic range extension scheme. The parasitic capacitance in fingerprint sensor cell has been eliminated with novel layout structure, and minimal size switch is used to avoid non-ideal effect. Power dissipation is also reduced with quiescent current control in buffer amplifier of sensor cell. A proof of concept chip, including the 16x16 sensor array, peripheral control circuit and analog to digital converter, is implemented in UMC 0.18 m Mixed- Signal 1P6M CMOS technology. The proposed capacitive fingerprint sensor readout circuit works at 1.8V power supply and operates at 4MHz clock rate. Capacitance value from 0fF to 65fF can be sensed, corresponding analog output voltage is from 1.3V to 0.2V and the digital output is 6 bits.[[note]]碩