A pixel-level automatic calibration circuit scheme for sensing initialization of a capacitive fingerprint sensor LSI

We propose a pixel-level automatic calibration circuit scheme that initializes a capacitive fingerprint sensor LSI to eliminate the influence of the surface condition, which is degraded by dirt during practical use. The calibration is executed by adjusting the variable capacitance in each pixel to make the sensed signals of all pixels the same. A fingerprint sensor LSI using the 0.5-/spl mu/m CMOS process/sensor process demonstrates that clear fingerprint images are always obtained by the scheme though the surface condition degrades. The proposed scheme ensures consistent clear image capture during long-term usage.