Patent ID: 7683640

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 is smaller than C FR ; 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; a second transistor having a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by an evaluate signal, the input terminal is connected to a second voltage VB, and the output terminal is connected to the fingerprint capacitor; a control circuit comprising: a third 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, wherein one input end of the operational amplifier is connected to the output terminal of the third transistor, and the other input end of the operational amplifier is connected to a first voltage VA; a reference capacitor C fb connected input and output ends of the operational amplifier; and a fourth 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.