Fingerprint sensing using measuring configurations with different principal directions of extensions

1. A method of determining a representation of a fingerprint pattern of a finger using a fingerprint sensor comprising a two-dimensional measuring arrangement including a plurality of measuring elements, each comprising a finger electrode spaced apart from said finger by a dielectric structure,

said method comprising the steps of, for each measurement position in a plurality of measurement positions:

providing a first measuring element configuration comprising:

a first set of sensing measuring elements defining an elongated first measuring arrangement portion including said measurement position and having a first principal direction of extension, the finger electrode of each measuring element in said first set of sensing measuring elements exhibiting a first time-varying sensing finger electrode potential; and

a first set of peripheral measuring elements defining a first peripheral measuring arrangement portion at least partly surrounding said first measuring arrangement portion, the finger electrode of each measuring element in said first set of peripheral measuring elements exhibiting a first peripheral finger electrode potential different from said first sensing finger electrode potential;

acquiring, using said first measuring element configuration, a first measurement value for said measurement position;

providing a second measuring element configuration comprising:

a second set of sensing measuring elements defining an elongated second measuring arrangement portion including said measurement position and having a second principal direction of extension different from said first principal direction of extension, the finger electrode of each measuring element in said second set of sensing measuring elements exhibiting a second time-varying sensing finger electrode potential; and

a second set of peripheral measuring elements defining a second peripheral measuring arrangement portion at least partly surrounding said second measuring arrangement portion, the finger electrode of each measuring element in said second set of peripheral measuring elements exhibiting a second peripheral finger electrode potential different from said second sensing finger electrode potential; and

acquiring, using said second measuring element configuration, a second measurement value for said measurement position, wherein said method further comprises the steps of:

determining a combined measurement value for each of said measurement positions based on said first measurement value and said second measurement value for each of said measurement positions; and

determining said representation of the fingerprint pattern based on said combined measurement value for each of said measurement positions.

2. The method according to claim 1 , wherein:

said first measuring element configuration further comprises:

a first set of guarding measuring elements defining an elongated first guarding measuring arrangement portion having said first principal direction of extension and being adjacent to said first sensing measuring arrangement portion, the finger electrode of each measuring element in said first set of guarding measuring elements exhibiting a first guarding finger electrode potential different from said first peripheral finger electrode potential; and

said second measuring element configuration further comprises:

a second set of guarding measuring elements defining an elongated second guarding measuring arrangement portion having said second principal direction of extension and being adjacent to said second sensing measuring arrangement portion, the finger electrode of each measuring element in said second set of guarding measuring elements exhibiting a second guarding finger electrode potential different from said second peripheral finger electrode potential.

3. The method according to claim 2 , wherein:

said first measuring element configuration further comprises:

a third set of guarding measuring elements defining an elongated third guarding measuring arrangement having said first principal direction of extension and being adjacent to said first set of guarding measuring elements, the finger electrode of each measuring element in said third set of guarding measuring elements exhibiting a third guarding finger electrode potential different from said first guarding finger electrode potential and different from said first peripheral finger electrode potential; and

said second measuring element configuration further comprises:

a fourth set of guarding measuring elements defining an elongated fourth guarding measuring arrangement having said second principal direction of extension and being adjacent to said second set of guarding measuring elements, the finger electrode of each measuring element in said fourth set of guarding measuring elements exhibiting a fourth guarding finger electrode potential different from said second guarding finger electrode potential and different from said second peripheral finger electrode potential.

4. The method according to claim 1 , wherein:

said first sensing finger electrode potential is time-varying in relation to said first peripheral finger electrode potential in such a way that a potential difference between said first sensing finger electrode potential and said first peripheral finger electrode potential changes from being a first potential difference at a first point in time to being a second potential difference at a second point in time; and

said second sensing finger electrode potential is time-varying in relation to said second peripheral finger electrode potential in such a way that a potential difference between said second sensing finger electrode potential and said second peripheral finger electrode potential changes from being a third potential difference at a third point in time to being a fourth potential difference at a fourth point in time.

5. The method according to claim 4 , wherein:

each measuring element in said plurality of measuring elements comprises charge amplifier circuitry controllable to provide a sensing signal indicative of a charge on the finger electrode of said measuring element.

6. The method according to claim 5 , wherein:

the step of acquiring said first measurement value comprises sampling a first sensing signal provided by said charge amplifier circuitry comprised in a measuring element in said first set of sensing measuring elements at said first point in time, and sampling said first sensing signal at said second point in time; and

the step of acquiring said second measurement value comprises sampling a second sensing signal provided by said charge amplifier circuitry comprised in a measuring element in said second set of sensing measuring elements at said third point in time, and sampling said second sensing signal at said fourth point in time.

7. The method according to claim 1 , wherein said two-dimensional measuring arrangement is a measuring element array with said plurality of measuring elements arranged in rows and columns,

wherein said first principal direction of extension is parallel to said columns, and said second principal direction of extension is parallel to said rows.

8. The method according to claim 1 , wherein:

said first measurement value is based on a signal acquired from a single measuring element, in said first set of measuring elements, arranged at said measurement position; and

said second measurement value is based on a signal acquired from a single measuring element, in said second set of measuring elements, arranged at said measurement position.

9. The method according to claim 1 , wherein:

said first measurement value is based on a difference between signals from mutually adjacent measuring elements, in said first set of measuring elements; and

said second measurement value is based on a difference between signals from mutually adjacent measuring elements, in said second set of measuring elements.

10. The method according to claim 1 , wherein:

said first measurement value is acquired, using said first measuring element configuration, simultaneously for a plurality of measurement positions included in said first measuring arrangement portion; and

said second measurement value is acquired, using said second measuring element configuration, simultaneously for a plurality of measurement positions included in said second measuring arrangement portion.

11. A fingerprint sensing system comprising:

a two-dimensional measuring arrangement including a plurality of measuring elements, each measuring element in said plurality of measuring elements comprising a finger electrode;

measurement control circuitry; and

image processing circuitry,

wherein said measuring arrangement is configurable, by said measurement control circuitry, in:

a first measuring element configuration comprising:

a first set of sensing measuring elements defining a first measuring arrangement portion having a first principal direction of extension, the finger electrode of each measuring element in said first set of sensing measuring elements exhibiting a first sensing finger electrode potential; and

a first set of peripheral measuring elements defining a first peripheral measuring arrangement portion at least partly surrounding said first measuring arrangement portion, the finger electrode of each measuring element in said first set of peripheral measuring elements exhibiting a first peripheral finger electrode potential different from said first sensing finger electrode potential; and

a second measuring element configuration comprising:

a second set of sensing measuring elements defining a second measuring arrangement portion having a second principal direction of extension, the finger electrode of each measuring element in said second set of sensing measuring elements exhibiting a second sensing finger electrode potential; and

a second set of peripheral measuring elements defining a second peripheral measuring arrangement portion at least partly surrounding said second measuring arrangement portion, the finger electrode of each measuring element in said second set of peripheral measuring elements exhibiting a second peripheral finger electrode potential different from said second sensing finger electrode potential,

wherein said measurement control circuitry is configured to:

control said measuring arrangement to acquire a first measurement value for each of said measurement positions, using said first measuring element configuration; and

control said measuring arrangement to acquire a second measurement value for each of said measurement positions, using said second measuring element configuration,

wherein said image processing circuitry is configured to:

determine a combined measurement value for each of said measurement positions based on said first measurement value and said second measurement value for each of said measurement positions; and

determine a representation of the fingerprint pattern based on said combined measurement value for each of said measurement positions.

12. The fingerprint sensing system according to claim 11 , wherein:

said first measuring element configuration further comprises a first set of guarding measuring elements defining an elongated first guarding measuring arrangement portion having said first principal direction of extension and being adjacent to said first sensing measuring arrangement portion;

said measurement control circuitry is configured to control said measuring arrangement to provide a first guarding finger electrode potential different from said first peripheral finger electrode potential to the finger electrode of each measuring element in said first set of guarding measuring elements;

said second measuring element configuration further comprises a second set of guarding measuring elements defining an elongated second guarding measuring arrangement portion having said second principal direction of extension and being adjacent to said second sensing measuring arrangement portion; and

said measurement control circuitry is configured to control said measuring arrangement to provide a second guarding finger electrode potential different from said second peripheral finger electrode potential to the finger electrode of each measuring element in said second set of guarding measuring elements.

13. The fingerprint sensor according to claim 12 , wherein:

said first measuring element configuration further comprises a third set of guarding measuring elements defining an elongated third guarding measuring arrangement portion having said first principal direction of extension and being adjacent to said first guarding measuring arrangement portion;

said measurement control circuitry is configured to control said measuring arrangement to provide a third guarding finger electrode potential different from said first guarding finger potential and said first peripheral finger electrode potential to the finger electrode of each measuring element in said third set of guarding measuring elements;

said second measuring element configuration further comprises a fourth set of guarding measuring elements defining an elongated fourth guarding measuring arrangement portion having said second principal direction of extension and being adjacent to said second guarding measuring arrangement portion; and

said measurement control circuitry is configured to control said measuring arrangement to provide a fourth guarding finger electrode potential different from said second guarding finger potential and said second peripheral finger electrode potential to the finger electrode of each measuring element in said fourth set of guarding measuring elements.

14. An electronic device, comprising:

the fingerprint sensing system according to claim 11 ; and

processing circuitry configured to:

acquire a representation of a fingerprint pattern of a user from said fingerprint sensing system;

authenticate said user based on said representation; and

perform at least one user-requested process only if said user is authenticated based on said representation.