Fingerprint sensing system and method utilizing edge-compensating structure

1. A fingerprint sensing system for sensing a fingerprint pattern of a finger, comprising:

a sensor array including a plurality of electrically conductive sensing structures;

read-out circuitry connected to each of said sensing structures for providing sensing signals indicative of a capacitive coupling between said sensing structures and said finger;

first signal providing circuitry for providing a first time-varying voltage signal to a set of the sensing structures in the plurality of sensing structures;

at least one electrically conductive edge-compensating structure arranged outside said sensor array; and

second signal providing circuitry for providing a second time-varying voltage signal to said at least one edge-compensating structure.

2. The fingerprint sensing system according to claim 1 , wherein said second signal providing circuitry is configured to provide said second time-varying voltage signal in synchronization with said first time-varying voltage signal.

3. The fingerprint sensing system according to claim 1 , wherein said read-out circuitry comprises:

a plurality of sensing circuits, each sensing circuit in said plurality of sensing circuits being arranged underneath, and being connected to, a respective set of sensing structures in said plurality of sensing structures; and

signal routing and conditioning circuitry for routing or conditioning signals to or from said plurality of sensing circuits,

said signal routing and conditioning circuitry at least partly being arranged underneath said at least one edge compensating structure.

4. The fingerprint sensing system according to claim 1 , wherein said sensor array, said read-out circuitry and said at least one edge-compensating structure are included in a fingerprint sensor component.

5. The fingerprint sensing system according to claim 4 , wherein said fingerprint sensor component comprises:

a component substrate;

active circuitry formed on said component substrate; and

a plurality of metal layers on said active circuitry.

6. The fingerprint sensing system according to claim 5 , wherein said plurality of sensing structures and said at least one edge-compensating structure are formed in a top-most metal layer in said plurality of metal layers.

7. The fingerprint sensing system according to claim 1 , wherein:

the sensing structures in said sensor array are arranged in rows and columns; and

said fingerprint sensing system comprises a plurality of edge-compensating structures, including:

a plurality of left proximal edge-compensating structures, each being arranged to the left of a corresponding one of said rows; and

a plurality of right proximal edge-compensating structures, each being arranged to the right of a corresponding one of said rows.

8. The fingerprint sensing system according to claim 7 , wherein said second signal providing circuitry is connected to each of said left proximal edge-compensating structures, and to each of said right proximal edge-compensating structures, and controllable to provide said second time-varying voltage signal to at least one of a set of said left proximal edge-compensating structures and a set of said right proximal edge-compensating structures.

9. The fingerprint sensing system according to claim 8 , wherein said second signal providing circuitry is controllable to simultaneously provide said second time-varying voltage signal to at least one of said left proximal edge-compensating structures aligned with one row of sensing structures, and to at least one of said right proximal edge-compensating structures aligned with said row of sensing structures.

10. The fingerprint sensing system according to claim 7 , wherein said plurality of edge-compensating structures further includes:

a plurality of left distal edge-compensating structures, each being arranged to the left of a corresponding one of said left proximal edge-compensating structures; and

a plurality of right distal edge-compensating structures, each being arranged to the right of a corresponding one of said right proximal edge-compensating structures.

11. The fingerprint sensing system according to claim 10 , wherein said second signal providing circuitry is connected to each of said left distal edge-compensating structures, and to each of said right distal edge-compensating structures, and controllable to provide a third time-varying voltage signal to at least one of a set of said left distal edge-compensating structures and a set of said right distal edge-compensating structures.

12. The fingerprint sensing system according to claim 1 , wherein said first signal providing circuitry is controllable to provide said first time-varying voltage signal to a set of said sensing structures in said plurality of sensing structures.

13. The fingerprint sensing system according to claim 12 , wherein:

said read-out circuitry comprises a plurality of sensing circuits, each sensing circuit in said plurality of sensing circuit being connected to a respective set of sensing structures in said plurality of sensing structures;

each sensing circuit in said plurality of sensing circuits comprises a charge amplifier including a first input connected to said set of sensing structures, a second input, an output, a feedback capacitor between said first input and said output, said charge amplifier being configured in such a way that a change in potential at said second input results in a substantially identical change in potential at said first input; and

said first signal providing circuitry is connected to said second input.

14. The fingerprint sensing system according to claim 13 , wherein:

said fingerprint sensing system comprises a semiconductor substrate;

said charge amplifier comprises a transistor formed in a well in said semiconductor substrate, said transistor having a gate constituting said first input,

an interface between said well and said substrate is configured in such a way that current can be prevented from flowing between said well and said substrate; and

said first signal providing circuitry is further connected to said well.

15. The fingerprint sensing system according to claim 1 , wherein said fingerprint sensing system further comprises:

finger detecting circuitry connected to said at least one edge-compensating structure for providing a finger detection signal indicative of a capacitive coupling between said at least one edge-compensating structure and said finger.

16. A method of sensing a fingerprint pattern of a finger, using a finger sensing system comprising:

a sensor array including a plurality of electrically conductive sensing structures;

read-out circuitry connected to each of said sensing structures;

first signal providing circuitry;

at least one electrically conductive edge-compensating structure arranged outside said sensor array; and

second signal providing circuitry,

said method comprising the steps of:

controlling said first signal providing circuitry to provide a first time-varying voltage signal to a set of the sensing structures in the plurality of sensing structures;

controlling said second signal providing circuitry to provide a second time-varying voltage signal to said at least one edge-compensating structure; and

controlling said read-out circuitry to provide sensing signals indicative of a capacitive coupling between said sensing structures and said finger.