Patent ID: 7683638

Claim:
A capacitive fingerprint sensor, comprising: a sensor cell comprising: a fingerprint capacitor having a capacitance that is either a valley capacitance C FV or a ridge capacitance C FR , and C FV being smaller than C FR ; and a first transistor having a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a scan line, the input terminal is connected to the fingerprint capacitor, and the output terminal is connected to a readout line; and a control circuit comprising: a second transistor having a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a first reset line and the input terminal is connected to the readout line; an operational amplifier, with one input end of the operational amplifier connected to the output terminal of the second transistor; a reference capacitor having capacitance C fb and disposed between input and output ends of the operational amplifier; a third transistor having a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a second reset line, and the input and output terminals are connected to the input and output ends of the operational amplifier, respectively; and a multiplexer connected to another input end of the operational amplifier, wherein inputs of the multiplexer are connected to a first voltage VA and a second voltage VB.