Fingerprint identification system and electronic device

1. A fingerprint identification system, comprising:

a plurality of first pixel circuits, a first pixel circuit in the plurality of first pixel circuits forming a contact capacitance with a finger;

a first sensing circuit, coupled to the first pixel circuit, for sensing the contact capacitance and outputting a first output signal, wherein the first output signal contains a big signal component and a small signal component, and the small signal component correlates with a change amount of the contact capacitance, and the big signal component comprises a signal component influenced by parasitic capacitance, temperature and/or noise;

at least one second pixel circuit;

a second sensing circuit, coupled to a second pixel circuit of the at least one second pixel circuit, for outputting a second output signal, wherein the second output signal is equal to the big signal component; and

a differential amplifying circuit, coupled to the first sensing circuit and the second sensing circuit, for amplifying a difference value between the first output signal and the second output signal to generate an amplifying output signal, wherein the amplifying output signal correlates with the small signal component;

wherein the second pixel circuit comprises:

a contact layer, coupled to a first driving circuit to receive a first drive signal, the contact layer receiving a contact of the finger;

a first shield layer, disposed below the contact layer;

a first metal layer, disposed below the first shield layer, and coupled to a second driving circuit to receive a second drive signal; and

a second metal layer, disposed below the first metal layer;

wherein the first shield layer and the second metal layer are coupled to the second driving circuit to receive a third drive signal; and

wherein the first metal layer is coupled to the second sensing circuit.

2. The fingerprint identification system according to claim 1 , wherein in a driving phase, the first driving circuit drives the contact layer to a positive voltage, and the second driving circuit drives the first shield layer, the first metal layer and the second metal layer to the positive voltage; and in a sensing phase, the first driving circuit provides the contact layer with a first voltage.

3. The fingerprint identification system according to claim 1 , wherein the second pixel circuit further comprises a third metal layer having the same horizontal position as the second metal layer and spaced with the second metal layer, and the third metal layer receives a fixed voltage.

4. The fingerprint identification system according to claim 1 , wherein the second pixel circuit further comprises a second shield layer having the same horizontal position as the first shield layer and spaced with the first shield layer, and the second shield layer receives a fixed voltage.

5. The fingerprint identification system according to claim 1 , wherein the first pixel circuit comprises:

a contact layer for receiving a contact of the finger, the contact layer forming the contact capacitance with the finger, and the contact layer coupled to a driving circuit and the sensing circuit; and

a first shield layer, disposed below the contact layer.

6. The fingerprint identification system according to claim 5 , wherein in a driving phase, the driving circuit drives the contact layer to a positive voltage.

7. The fingerprint identification system according to claim 5 , wherein the first pixel circuit further comprises a second shield layer having the same horizontal position as the first shield layer and spaced with the first shield layer, and the second shield layer receives a fixed voltage.

8. The fingerprint identification system according to claim 1 , wherein the differential amplifying circuit is a programmable gain amplifier.

9. An electronic device, wherein the electronic device comprises:

an operating circuit; and

a fingerprint identification system, coupled to the operating circuit, and the fingerprint identification system comprising:

a plurality of first pixel circuits, a first pixel circuit in the plurality of first pixel circuits forming a contact capacitance with a finger;

a first sensing circuit, coupled to the first pixel circuit, for sensing the contact capacitance and outputting a first output signal, wherein the first output signal contains a big signal component and a small signal component, and the small signal component correlates with a change amount of the contact capacitance, and the big signal component comprises a signal component influenced by parasitic capacitance, temperature and/or noise;

at least one second pixel circuit;

a second sensing circuit, coupled to a second pixel circuit of the at least one second pixel circuit, for outputting a second output signal, wherein the second output signal is equal to the big signal component; and

a differential amplifying circuit, coupled to the first sensing circuit and the second sensing circuit, for amplifying a difference value between the first output signal and the second output signal to generate an amplifying output signal, wherein the amplifying output signal correlates with the small signal component;

wherein the second pixel circuit comprises;

a contact layer, coupled to a first driving circuit to receive a first drive signal, the contact layer receiving a contact of the finger;

a first shield layer, disposed below the contact layer;

a first metal layer, disposed below the first shield layer, and coupled to a second driving circuit to receive a second drive signal; and

a second metal layer, disposed below the first metal layer;

wherein the first shield layer and the second metal layer are coupled to the second driving circuit to receive a third drive signal; and

wherein the first metal layer is coupled to the second sensing circuit.