Abstract
In this paper, we introduce a differential sensing technique for CMOS capacitive fingerprint detection. It employs a new capacitive-sensing cell structure with charge sharing detection and readout circuit. The proposed technique also can eliminate the effect of parasitic capacitances by employing parasitic insensitive switched-capacitor structure and so increases the sensitivity even under severe noisy conditions. It can also overcome the performance degradation caused by various conditions of finger surface by using a differential integrator and adjusting its number of integrations. In addition, the proposed architecture allows parallel detection of all sensing channels. It can, therefore, substantially speed up the detection process compared with conventional architectures. We implemented a prototype fingerprint sensor chip with an array of 20 × 16 sensor cells using a 130 nm CMOS process. Simulation experiments demonstrated that the proposed architecture provided an SNR gain of 54 dB, whereas a conventional single line sensing gives an SNR gain of only 13 dB.
Highlights
Nowadays, the increasing requirements on tighter security are raising the demand of the accuracy and performance levels of biometric sensing techniques such as fingerprint sensing.User authentication becomes one of the major challenges in the era of mobile banking, FinTech, and the Internet of Things (IoT)
We present a new architecture for the stand-alone CMOS capacitive fingerprint sensing based on a new cell structure with charge sharing detection and a parallel readout circuit with differential integrators
We implemented the proposed fingerprint sensing circuit and fabricated a test chip using nm CMOS process. It consists of a proposed fingerprint sensor array of 20 × 16 sensor cells and a a 130 nm CMOS process
Summary
The increasing requirements on tighter security are raising the demand of the accuracy and performance levels of biometric sensing techniques such as fingerprint sensing. For mass production of the ultrasonic fingerprint sensors for the in-cell phones display fingerprint, it needs complex manufacturing steps and its fingerprint recognition speed is slow [5,17] It needs to achieve a high performance at a lower or similar cost and power consumption of the capacitive technology. The optical fingerprint sensor is added under the display of the cell phone to capture the fingerprint image where a special position of the display works as a fingerprint scanner This prototype is embedded under the display; it has the drawbacks of working under the strong light and dealing with certain circumstances such as dry fingers and wet fingers.
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