Patent ID: 7663380

Claim:
A capacitive fingerprint sensor, comprising: a first transistor having a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a first readout select line, and the input terminal is connected to a first bias voltage VA; a second transistor having a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by the first readout select line, and the input terminal is connected to a second bias voltage VB; a fingerprint capacitor C F connected in parallel to the output terminal of the second transistor, wherein the fingerprint capacitor has a capacitance that is either a valley capacitance C FV or a ridge capacitance C FR ; a reference capacitor C s connected in parallel to the output terminal of the first transistor, wherein the reference capacitor has a capacitance C s , and C FV <C s <C FR ; a third transistor having a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a second readout select line, the input terminal is connected to the fingerprint capacitor, the output terminal is connected to the reference capacitor, and the second readout select line is immediately next to the first readout select line; and a fourth 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 reference capacitor, and the output terminal is connected to a readout line.