Active sensing element for acoustic imaging systems

• US 10,061,963 B2
• Filed: 08/28/2017
• Issued: 08/28/2018
• Est. Priority Date: 09/30/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Yazdandoost, Mohammad Yeke, Gozzini, Giovanni, Bussat, Jean-Marie
• Primary Examiner(s): Werner, Brian
• Application Number:
  US15/688,639
• Publication Number:
  US 20170357839A1
• Time in Patent Office: 365 Days
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

An acoustic fingerprint imaging system having a plurality of acoustic elements, each acoustic element including a transducer, and independent drive and sense circuitry is disclosed. Drive circuitry may require higher voltage than low voltage sense circuitry. Many embodiments described herein include a ground shifting controller to apply a voltage bias to the low voltage sense circuitry during a drive operation, in order to prevent electrical damage to the sense circuitry.

Claims

1. An acoustic imaging sensor comprising:

a piezoelectric element operable in a drive mode and a sense mode;

a sense circuit coupled to the piezoelectric element and configured to obtain a voltage signal from the piezoelectric element when in the sense mode, the voltage signal corresponding to at least a portion of a pixel of an acoustic image; and

a ground-shifting controller configured to increase a ground and a source of the sense circuit approximately to a drive voltage when in the drive mode.

2. The acoustic imaging sensor of claim 1, further comprising:

a drive voltage node; and

a drive circuit configured to couple the piezoelectric element to the drive voltage node when in the drive mode.

3. The acoustic imaging sensor of claim 2, wherein the ground-shifting controller is configured to connect the drive voltage node to a system ground when in the sense mode.

4. The acoustic imaging sensor of claim 2, wherein the drive voltage node is coupled to a high voltage source.

5. The acoustic imaging sensor of claim 2, wherein the sense circuit is coupled to a low voltage source.

6. The acoustic imaging sensor of claim 1, wherein:

the piezoelectric element is a first piezoelectric element; and

the acoustic imaging sensor further comprises;

an array of piezoelectric elements, including the first piezoelectric element, coupled to an interior surface of a substrate.

7. The acoustic imaging sensor of claim 6, wherein the array of piezoelectric elements is configured to capture an image of a fingerprint in contact with an exterior surface of the substrate.

8. The acoustic imaging sensor of claim 7, wherein the substrate is formed from one of the group consisting of glass, plastic, sapphire, and metal.

9. The acoustic imaging sensor of claim 1, wherein the piezoelectric element is positioned below a display.

10. The acoustic imaging sensor of claim 1, wherein the piezoelectric element is positioned below a button.

11. The acoustic imaging sensor of claim 1, wherein the piezoelectric element comprises a lead-free piezoelectric material.

12. A method of operating an acoustic sensor element in a drive mode, the method comprising:

increasing a ground of a low-voltage sense circuit coupled to the acoustic sensor element to a voltage approximately equal to a high-voltage drive signal;

increasing a source of the low-voltage sense circuit such that a potential difference between the source and the ground of the low-voltage sense circuit does not exceed a selected low-voltage threshold; and

after increasing the ground and source of the low-voltage sense circuit, applying the high-voltage drive signal to the acoustic sensor element.

13. The method of claim 12, wherein the high-voltage drive signal has a sinusoidal waveform.

14. The method of claim 12, further comprising increasing the source of the low-voltage sense circuit above the ground.

15. The method of claim 12, wherein the ground and source are biased to the same voltage.

16. The method of claim 12, wherein when the acoustic sensor element is in a sense mode, the method comprises:

decreasing the ground of the low-voltage sense circuit to a system ground; and

decreasing the source of the low-voltage sense circuit to a voltage above the system ground such that a potential difference between the source and the ground of the low-voltage sense circuit does not exceed a selected threshold.

17. A method of operating an acoustic imaging sensor, the method comprising:

operating in a drive mode by;

increasing a ground of a low-voltage sense circuit coupled to an acoustic sensor element array to a voltage approximately equal to a high-voltage drive signal;

increasing a source of the low-voltage sense circuit such that a potential difference between the source and the ground of the low-voltage sense circuit does not exceed a selected threshold; and

applying the high-voltage drive signal to at least one acoustic sensor element of the acoustic sensor element array; and

operating in a sense mode, after applying the high-voltage drive signal to the at least one acoustic sensor element, by;

decreasing the ground of the low-voltage sense circuit;

decreasing the source of the low-voltage sense circuit such that the potential difference between the source and the ground does not exceed the selected threshold; and

obtaining at least one voltage signal from the at least one acoustic sensor element.

18. The method of claim 17, further comprising amplifying the at least one voltage signal.

19. The method of claim 18, further comprising correlating the at least one voltage signal to at least one pixel of an output image.

20. The method of claim 18, wherein:

the high-voltage drive signal is generated by a drive circuit; and

the method further comprising, in the sense mode, grounding a voltage supply line of the drive circuit.