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Impedance-Sensing Circuit Techniques for Integration of a Fraud Detection Function Into a Capacitive Fingerprint Sensor

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7 Author(s)
Shimamura, T. ; NTT Microsyst. Integration Labs., Atsugi, Japan ; Morimura, H. ; Shimoyama, N. ; Sakata, T.
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This paper describes techniques for an impedance-sensing circuit integrated into a capacitive fingerprint sensor to prevent spoofing with a fake finger. We have reported a sensor chip with an embedded impedance-sensing function. We proposed an impedance-sensing circuit that features current-to-voltage con- version using a unity gain buffer. Here, the design of the sensing circuit is discussed. The detectable impedance range and the sensitivity are analyzed within the impedance range for various human fingers. A test chip with the proposed circuit was fabricated using 0.5-μm CMOS/sensor processes. The results confirm that the difference in impedance between a real finger and a fake finger is detected without any degradation of the original characteristics of the fingerprint sensor chip.

Published in:

Sensors Journal, IEEE  (Volume:12 ,  Issue: 5 )
Biometrics Compendium, IEEE