System and method for controlling a signal in a fingerprint sensing device

1. A method for controlling a capacitive fingerprint sensing device for sensing a fingerprint pattern of a finger, said capacitive fingerprint sensing device comprising a plurality of sensing elements, each sensing element comprising:

a protective dielectric top layer to be touched by said finger;

an electrically conductive sensing structure arranged underneath said top layer;

sensing circuitry configured to provide an analog sensing signal indicative of a distance between said finger and said sensing structure, said fingerprint sensing device further comprising:

timing circuitry configured to control a timing of a drive signal, the drive signal being configured to provide a change in potential difference between the finger and the sensing structure; the method comprising:

forming a drive signal comprising a sequence of pulses, wherein a delay between consecutive pulses is controllable by said timing circuitry.

2. The method according to claim 1 , wherein the pulses have a fixed duty cycle determining a minimum separation between consecutive pulses.

3. The method according to claim 1 , wherein the drive signal comprises a sequence of pulses arranged in groups of pulses, where a delay between consecutive groups of pulses is larger than a delay between consecutive pulses within a group, and wherein a delay between consecutive pulses is the same for all pulses within a group.

4. The method according to claim 3 , comprising providing a drive signal comprising a plurality of sequences of pulses, each sequence comprising a plurality of groups of pulses, and controlling a delay between consecutive sequences of pulses, wherein a delay between consecutive sequences is larger than a delay between consecutive groups.

5. The method according to claim 1 , comprising providing a random delay between consecutive pulses.

6. The method according to claim 1 , wherein a delay between consecutive pulses is in the range of 1 to 20 clock cycles.

7. The method according to claim 1 , wherein a delay between consecutive pulses is based on an operating frequency of a component in an electronic device in which the fingerprint sensing device is arranged.

8. The method according to claim 7 , wherein a fixed delay is provided between consecutive pulses such that said drive signal is characterized by a frequency different from the operating frequency.

9. The method according to claim 7 , wherein the component is a touch screen display of an electronic device.

10. The method according to claim 1 , further comprising detecting the use of an antenna in an electronic device in which the fingerprint sensing device is arranged, and increasing a delay between consecutive pulses compared to if the antenna is not in use.

11. A capacitive fingerprint sensing device for sensing a fingerprint pattern of a finger, said capacitive fingerprint sensing device comprising a plurality of sensing elements, each sensing element comprising:

a protective dielectric top layer to be touched by said finger;

an electrically conductive sensing structure arranged underneath said top layer;

sensing circuitry configured to provide an analog sensing signal indicative of a distance between said finger and said sensing structure, said fingerprint sensing device further comprising:

timing circuitry configured to control a timing of a drive signal, the drive signal being configured to provide a change in potential difference between the finger and the sensing structure;

wherein the timing circuitry is configured to form a drive signal comprising a sequence of pulses, wherein a delay between consecutive pulses is controllable by said timing circuitry.

12. The sensing device according to claim 11 , further comprising an electrically conductive bezel arranged adjacent to a sensing surface of said fingerprint sensing device, wherein said drive signal is provided to said bezel.

13. The sensing device according to claim 11 , wherein said drive signal is provided to a sensing element of said sensing circuitry.

14. The sensing device according to claim 11 , wherein said drive signal is provided to a reference ground connection of said sensing circuitry.

15. The sensing device according to claim 11 , wherein said timing circuitry comprises drive signal circuitry configured to form and provide said drive signal to said sensing circuitry.

16. An electronic device comprising:

a fingerprint sensing device according to claim 11 ; and

a component operating at a predetermined operating frequency; wherein the timing circuitry is configured to form a drive signal comprising a delay between consecutive pulses based on the predetermined operating frequency.

17. The electronic device according to claim 16 , wherein the timing circuitry is configured to configured to form a drive signal comprising a fixed delay between consecutive pulses such that said drive signal exhibits a fixed frequency different from the operating frequency.

18. The electronic device according to claim 16 , wherein the timing circuitry is configured to form a drive signal comprising a random delay between consecutive pulses.

19. The electronic device according to claim 17 , further comprising an antenna, wherein the fingerprint sensing device is configured to detect a use of the antenna, and to increase a delay between consecutive pulses compared to if the antenna is not in use.