Active Sensing Element for Acoustic Imaging Systems

• US 20170357839A1
• Filed: 08/28/2017
• Published: 12/14/2017
• Est. Priority Date: 09/30/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Yazdandoost, Mohammad Yeke, Gozzini, Glovanni, Bussat, Jean-Marie
• Granted Patent: US 10,061,963 B2
• Time in Patent Office: 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 high voltage node;

a low voltage node;

an acoustic element in communication with a bottom surface of a substrate, configured to produce an acoustic input into the substrate, the acoustic element comprising;

an ultrasonic transducer;

a drive circuit configured to couple the ultrasonic transducer to the high voltage node and generate the acoustic input; and

a sense circuit coupled to the low voltage node and configured to obtain an acoustic output from the substrate; and

a controller configured to increase a voltage bias of the sense circuit when the drive circuit is active.

2. The acoustic imaging sensor of claim 1, wherein the acoustic imaging sensor is a biometric imaging sensor.

3. The acoustic imaging sensor of claim 1, wherein the acoustic imaging sensor is configured to capture an image of a fingerprint.

4. The acoustic imaging sensor of claim 1, wherein the substrate is formed from an optically transparent material.

5. The acoustic imaging sensor of claim 1, wherein the substrate is formed from one of the group consisting of glass, sapphire, and metal.

6. The acoustic imaging sensor of claim 1, wherein the acoustic transducer is formed from a material configured to expand in response to a high voltage pulse.

7. The acoustic imaging sensor of claim 1, wherein the high voltage node is coupled to a high voltage source configured to output 100 volts.

8. The acoustic imaging sensor of claim 1, wherein the low voltage node is coupled to a low voltage source configured output less than 10 volts.

9. The acoustic imaging sensor of claim 1, wherein the controller is configured to raise the voltage bias of the sense circuit to a voltage approximately equal to the voltage of the high voltage node.

10. The acoustic imaging sensor of claim 9, wherein raising the voltage bias of the sense circuit to a voltage approximately equal to the voltage of the high voltage node comprises ground shifting the sense circuit.

11. The acoustic imaging sensor of claim 9, wherein ground shifting the sense circuit comprises applying a direct current voltage bias to the low voltage node and to a circuit ground of the sense circuit.

12. A method of driving an acoustic element comprising a high voltage drive circuit and a low voltage sense circuit, the method comprising:

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

applying a high voltage drive signal to an ultrasonic transducer coupled to the high voltage drive circuit.

13. The method of claim 12, wherein the acoustic element comprises an acoustic transducer formed from a material configured to expand in response to a high voltage pulse.

14. The method of claim 12, wherein the high voltage drive circuit is coupled to a high voltage source configured to output 100 volts.

15. The method of claim 14, wherein the low voltage sense circuit is coupled to a low voltage node configured to output approximately 3.3 volts.

16. The method of claim 12, wherein increasing a voltage bias of the low voltage sense circuit comprises raising the voltage bias of the low voltage sense circuit to a voltage approximately equal to the voltage of the high voltage drive circuit.

17. The method of claim 16, wherein raising the voltage bias of the low voltage sense circuit to a voltage approximately equal to the voltage of the high voltage drive circuit comprises ground shifting the low voltage sense circuit.

18. The method of claim 17, wherein ground shifting the sense circuit comprises applying a direct current voltage bias to the low voltage node and to a circuit ground of the sense circuit.

19. A method of reading an output of an acoustic element of an acoustic fingerprint imaging system comprising a high voltage drive circuit and a low voltage sense circuit, the method comprising:

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

decreasing a voltage bias of the high voltage drive circuit such that the potential difference between a voltage source of the high voltage drive circuit and a circuit ground of the high voltage drive circuit is approximately zero volts;

applying a reset voltage signal to the low voltage sense circuit; and

measuring a voltage output from the low voltage sense circuit.

20. The method of claim 19, wherein the acoustic element comprises an acoustic transducer formed from a material configured to expand in response to a high voltage pulse.

21. The method of claim 19, wherein the high voltage drive circuit is coupled to a high voltage source configured to output 100 volts.

22. The method of claim 19, wherein the low voltage sense circuit is coupled to a low voltage node configured to output approximately 3.3 volts.