Capacitive-Sensing Circuit Technique for Image Quality Improvement on Fingerprint Sensor LSIs

This paper describes a new capacitive-sensing circuit technique that improves the quality of images captured with capacitive fingerprint sensor LSIs. The quality of the captured image depends on the surface condition of the finger. When the finger is dry, the electrical resistance of the finger surf...

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Bibliographic Details
Published in:IEEE journal of solid-state circuits 2010-05, Vol.45 (5), p.1080-1087
Main Authors: Shimamura, Toshishige, Morimura, Hiroki, Shigematsu, Satoshi, Nakanishi, Mamoru, Machida, Katsuyuki
Format: Article
Language:English
Subjects:
Applied sciences
Biometrics
Capacitive sensors
capacitive-sensing
Circuits
Design. Technologies. Operation analysis. Testing
dry finger
Drying
Electric potential
Electric resistance
Electronic equipment and fabrication. Passive components, printed wiring boards, connectics
Electronics
Exact sciences and technology
Fingerprint recognition
Fingerprint sensor LSI
Fingerprinting
Fingerprints
Fingers
General equipment and techniques
Image matching
Image quality
Image sensors
Instruments, apparatus, components and techniques common to several branches of physics and astronomy
Integrated circuits
Physics
Security management
Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
Sensors
Sensors (chemical, optical, electrical, movement, gas, etc.)
remote sensing
Surface resistance
Voltage control
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Description
Summary:This paper describes a new capacitive-sensing circuit technique that improves the quality of images captured with capacitive fingerprint sensor LSIs. The quality of the captured image depends on the surface condition of the finger. When the finger is dry, the electrical resistance of the finger surface is high. The finger surface resistance induces a voltage drop in the electrical potential of the finger surface (which should be grounded), which leads to poor image quality. To capture clear images even when the finger is dry, the circuit technique improves the image quality using the series resistance caused at the finger surface. The potential of the finger surface is controlled by an enhancement plate and a voltage control circuit. A test chip implementing this technique was fabricated on a 0.5 ¿m CMOS process and a sensor process. The chip captures a clear fingerprint image of a dry finger, confirming the effectiveness of the circuit technique for capturing clear fingerprint images independent of the finger surface condition with the capacitive fingerprint sensor LSIs.
ISSN:0018-9200
1558-173X
DOI:10.1109/JSSC.2010.2042525