Active baseline signal cancellation in fingerprint sensors

• US 10,074,002 B2
• Filed: 11/04/2016
• Issued: 09/11/2018
• Est. Priority Date: 10/08/2014
• Status: Active Grant

• Current Assignee: Shenzhen Goodix Technology Co., Ltd.
• Original Assignee: Shenzhen Goodix Technology Co., Ltd.
• Inventors: Pi, Bo, Yang, Mengta
• Primary Examiner(s): Yang, Qian
• Application Number:
  US15/344,506
• Publication Number:
  US 20170068837A1
• Time in Patent Office: 676 Days
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

In one aspect, a fingerprint sensor chip includes an array of senor pixels. At least one of the sensor pixels is designated as a reference sensor pixel and remaining sensor pixels in the array are designated to contribute to fingerprint data, The sensor chip includes a signal processing unit including amplifier circuitry to cancel out baseline signals from output signals of remaining sensor pixels based at least on an output signal of the reference sensor pixel.

Claims

1. A fingerprint sensor chip, comprising:

an array of senor pixels, wherein at least one of the sensor pixels is designated as a reference sensor pixel and remaining sensor pixels in the array are designated to contribute to fingerprint data;

the reference sensor pixel includes same fingerprint sensor components as the remaining sensor pixels;

each sensor of the array of sensor pixels generates an output signal including a baseline signal and a fingerprint signal, wherein a magnitude proportion of the baseline signal in the output signal is greater than that of the fingerprint signal in the output signal;

the output signal of the reference sensor pixel is used to generate a baseline cancellation signal; and

a signal processing unit including circuitry configured to cancel out baseline signals from output signals of remaining sensor pixels based on the baseline cancellation signal.

2. The fingerprint sensor chip of claim 1, wherein:

the circuitry to cancel out baseline signals is configured to cancel out the output signal of the reference sensor pixel from the output signals corresponding to the remaining sensor signals.

3. The fingerprint sensor chip of claim 2, wherein:

the signal processing unit includes an integrating amplifier for each of the remaining sensor pixels configured to amplify the baseline signal cancelled output signal of a corresponding remaining sensor pixel.

4. The fingerprint sensor chip of claim 1, wherein:

the signal processing unit includes a reference coupling capacitor for each of the remaining sensor pixels disposed on an electrical path to receive the output signal of the reference sensor pixel.

5. The fingerprint sensor chip of claim 1, wherein:

the signal processing unit includes a sensor coupling capacitor for each of the remaining sensor pixels disposed on an electrical path to receive the output signal of a corresponding sensor pixel.

6. The fingerprint sensor chip of claim 1, wherein:

the reference sensor pixel is positioned substantially near a center of the array of sensor pixels.

7. A method of cancelling a baseline signal in a fingerprint sensor chip, comprising:

responsive to an input indicating a fingerprint scan, generating, at an array of fingerprint sensor pixels, output signals including baseline signals and fingerprint signals, wherein a magnitude proportion of the baseline signals in the output signals are greater than that of the fingerprint signals in the output signals;

selecting one of the fingerprint sensor pixels as a reference fingerprint sensor pixel;

using the output signal corresponding to the selected reference fingerprint sensor pixel to generate a baseline cancellation signal;

cancelling out the baseline signals from remaining output signals corresponding to remaining sensor pixels based on the baseline cancellation signal;

wherein the reference sensor pixel includes same fingerprint sensor components as the remaining sensor pixels;

amplifying the baseline signal cancelled output signals corresponding to the remaining sensor pixels; and

using the amplified signals to generate fingerprint data.

8. The method of claim 7, comprising:

selecting additional ones of the sensor pixels as reference sensor pixel; and

using the output signals corresponding to the selected reference sensor pixels to cancel the baseline signals from the output signals of the remaining sensor pixels.

9. The method of claim 7, wherein using the output signals corresponding to the selected reference sensor pixels includes:

averaging the output signals corresponding to the selected reference sensor pixels; and

cancelling out the baseline signals from remaining output signals corresponding to remaining sensor pixels based on the baseline cancellation signal includes;

using the averaged output signal to cancel the baseline signals from the output signals of the remaining sensor pixels.

10. A method of cancelling a baseline signal in a fingerprint sensor chip, comprising:

responsive to an input indicating a fingerprint scan, generating, at an array of fingerprint sensor pixels, output signals including baseline signals and fingerprint signals, wherein a magnitude proportion of the baseline signals in the output signals are greater than that of the fingerprint signals in the output signals;

comparing the output signals with a preset reference signal;

when the preset reference signal satisfy a threshold percentage of the output signals, cancelling out the baseline signals from the output signals by performing the following;

using the preset reference signal to cancel out the baseline signals from the output signals generated at the array of sensor pixels;

amplifying the baseline signal cancelled output signals corresponding to the array of sensor pixels; and

using the amplified signals to generate fingerprint data.

11. The method of claim 10, wherein the using the amplified signals to generate the fingerprint data includes reading out the amplified signals from the array of sensor pixels each row or column of the array of sensor pixels at a time.

12. The method of claim 10, when the preset reference signal does not satisfy the threshold percentage of the output signals, the preset reference signal is adjusted and compared against the output signals of the sensor pixels to determine whether the adjusted reference signal satisfies the threshold percentage.

13. The method of claim 12, when the adjusted reference signal satisfies the threshold percentage of the output signals, cancelling out the baseline signals from the output signals by performing the following:

using the adjusted reference signal to cancel out the baseline signals from the output signals generated at the array of sensor pixels;

amplifying the baseline signal cancelled output signals corresponding to the array of sensor pixels; and

using the amplified signals to generate fingerprint data.

14. The method of claim 12, including incrementally adjusting the adjusted reference signal until the threshold percentage is satisfied.

15. A mobile device comprising:

a fingerprint sensor device; and

a protective cover disposed over the fingerprint sensor device, the protective cover including a dielectric material;

wherein the fingerprint sensor device includes a sensor chip, the sensor chip including;

an array of senor pixels, wherein one of the sensor pixels is designated as a reference sensor pixel and remaining sensor pixels in the array are designated to contribute to fingerprint data;

the reference sensor pixel includes same fingerprint sensor components as the remaining sensor pixels;

each sensor of the array of sensor pixels generates an output signal including a baseline signal and a fingerprint signal, wherein a magnitude proportion of the baseline signal in the output signal is greater than that of the fingerprint signal in the output signal;

the output signal of the reference sensor pixel is used to generate a baseline cancellation signal; and

a signal processing unit including circuitry configured to cancel out baseline signals from output signals of remaining sensor pixels based on the baseline cancellation signal.

16. The mobile device of claim 15, wherein:

the circuitry to cancel out baseline signals is configured to cancel out the output signal of the reference sensor pixel from the output signals corresponding to the remaining sensor signals.

17. The mobile device of claim 16, wherein:

the signal processing unit includes an integrating amplifier for each of the remaining sensor pixels configured to amplify the baseline signal cancelled output signal of a corresponding remaining sensor pixel.

18. The mobile device of claim 15, wherein:

the signal processing unit includes a reference coupling capacitor for each of the remaining sensor pixels disposed on an electrical path to receive the output signal of the reference sensor pixel.

19. The mobile device of claim 15, wherein:

the signal processing unit includes a sensor coupling capacitor for each of the remaining sensor pixels disposed on an electrical path to receive the output signal of a corresponding sensor pixel.

20. The mobile device of claim 15, wherein:

the reference sensor pixel is positioned substantially near a center of the array of sensor pixels.