Fingerprint identification system and electronic device

• US 10,474,865 B2
• Filed: 10/12/2017
• Issued: 11/12/2019
• Est. Priority Date: 09/27/2016
• Status: Active Grant

• Current Assignee: Shenzhen Goodix Technology Co., Ltd.
• Original Assignee: Shenzhen Goodix Technology Co., Ltd.
• Inventors: Chao, Kuohao, Yang, Mengta
• Primary Examiner(s): Werner, Brian
• Application Number:
  US15/782,843
• Publication Number:
  US 20180089488A1
• Time in Patent Office: 761 Days
• CPC Class Codes: G06F 2203/04107 Shielding in digitiser, i.e. guard or shielding arrangements, mostly for capacitive touchscreens, e.g. driven shields, driven grounds
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: G06V 40/1329 Protecting the fingerprint sensor against damage caused by the finger

Abstract

Provided is a fingerprint identification system, comprising: a plurality of first pixel circuits; a first sensing circuit for sensing a contact capacitance and outputting a first output signal, where 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; at least one second pixel circuit; a second sensing circuit for outputting a second output signal, where the second output signal is equal to the big signal component; and a differential amplifying circuit for amplifying a difference value between the first output signal and the second output signal so as to generate an amplifying output signal, where the amplifying output signal correlates with the small signal component.

Claims

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.