Active matrix capacitive fingerprint sensor with 1-TFT pixel architecture for display integration

• US 9,958,993 B2
• Filed: 06/30/2015
• Issued: 05/01/2018
• Est. Priority Date: 06/30/2015
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Akhavan Fomani, Arash, Hargreaves, Kirk, Smith, Patrick, Shepelev, Petr
• Primary Examiner(s): Shankar, Vijay
• Application Number:
  US14/788,604
• Publication Number:
  US 20170003777A1
• Time in Patent Office: 1,036 Days
• Field of Search: 345173-178
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

Embodiments described herein include a method for operating an input device by applying a charge voltage to a sense element through a first transistor that is between the sense element and a column output line and a first switch that is between the column output line and a drive voltage. The method also includes storing an electric charge on the sense element, wherein the electric charge comprises a magnitude corresponding to a feature of an input object. The method also includes driving a gate terminal of the first transistor low and disconnecting the charge voltage via the first switch. The method further includes transferring the electric charge to a feedback capacitor.

Claims

1. An input device, comprising:

a sensing pixel configured to sense an input object in a sensing region, wherein the sensing pixel comprises a sense element configured to store an electric charge, wherein the electric charge comprises a magnitude corresponding to a feature of the input object; and

a drive/readout circuit comprising;

an amplifier circuit connected to a feedback capacitor and a reset switch;

a first switch configured to connect and disconnect a column output line to a drive voltage; and

a second switch configured to connect and disconnect the column output line to the amplifier circuit;

wherein the drive/readout circuit is configured to;

apply the drive voltage to the sense element;

bias the column output line to ground while the sense element is disconnected from the column output line; and

read out a resulting signal from the sense element.

2. The input device of claim 1, wherein the resulting signal corresponds to a capacitance formed between the sense element and the input object in the sensing region.

3. The input device of claim 1, wherein the drive/readout circuit further comprises a feedback switch, wherein the feedback capacitor is configured to accumulate a charge over one or more charge and discharge cycles of the sense element using the feedback switch.

4. The input device of claim 3, wherein the feedback switch is further configured to connect and disconnect the feedback capacitor to an input of the amplifier circuit.

5. The input device of claim 1, wherein the drive/readout circuit further comprises a third switch configured to connect and disconnect the column output line to system ground, wherein the drive/readout circuit is configured to bias the column output line to ground by closing the third switch.

6. A method for operating an input device, comprising:

applying a drive voltage to a sense element via a first switch configured to connect and disconnect a column output line;

biasing the column output line to ground while the sense element is disconnected from the column output line via a second switch; and

reading out a resulting signal from the sense element.

7. The method of claim 6, wherein the resulting signal corresponds to a capacitance formed between the sense element and an input object in a sensing region.

8. The method of claim 6, wherein a feedback capacitor is configured to accumulate a charge over one or more charge and discharge cycles of the sense element using a feedback switch.

9. The method of claim 8, wherein the feedback switch is further configured to connect and disconnect the feedback capacitor to an input of an amplifier circuit.

10. A processing system for operating an input device, comprising:

a drive/readout circuit comprising;

an amplifier circuit connected to a feedback capacitor and a reset switch;

a first switch configured to connect and disconnect a column output line to a drive voltage; and

a second switch configured to connect and disconnect the column output line to the amplifier circuit;

wherein the drive/readout circuit is configured to;

apply the drive voltage to a sense element;

bias the column output line to ground while the sense element is disconnected from the column output line; and

read out a resulting signal from the sense element.

11. The processing system of claim 10, wherein the resulting signal corresponds to a capacitance formed between the sense element and an input object in a sensing region.

12. The processing system of claim 10, wherein the drive/readout circuit further comprises a feedback switch, wherein the feedback capacitor is configured to accumulate a charge over one or more charge and discharge cycles of the sense element using the feedback switch.

13. The processing system of claim 12, wherein the feedback switch is further configured to connect and disconnect the feedback capacitor to an input of the amplifier circuit.

14. The processing system of claim 10, wherein the drive/readout circuit further comprises a third switch configured to connect and disconnect the column output line to system ground, wherein the drive/readout circuit is configured to bias the column output line to ground by closing the third switch.

15. The processing system of claim 10, wherein the drive/readout circuit is configured to bias the column output line to ground by closing the second switch and the reset switch to bias the column output line to virtual ground.

16. The processing system of claim 10, wherein the amplifier circuit is a lower voltage circuit than the drive voltage.

17. The processing system of claim 10, wherein the drive/readout circuit is configured to address the sense element through a first transistor, wherein the first transistor has a gate terminal connected to a row select line, a second terminal connected to the column output line, and a third terminal connected to the sense element.

18. The processing system of claim 17, wherein the first transistor is a thin-film transistor.

19. The processing system of claim 10, wherein the sense element has a pitch suitable for distinguishing between features of a fingerprint.

20. The processing system of claim 19, wherein the pitch comprises a range of 20 to 100 microns.