FINGERPRINT SENSING SYSTEM WITH SENSING REFERENCE POTENTIAL PROVIDING CIRCUITRY
First Claim
1. A fingerprint sensing system for sensing a fingerprint pattern of a finger, said fingerprint sensing system comprising:
- a device connection interface for connection of said fingerprint sensing system to an electronic device, said device connection interface including a device reference potential input for receiving a device reference potential from said electronic device;
a sensing arrangement including;
a plurality of sensing structures, each being covered by a dielectric structure; and
read-out circuitry connected to each of said sensing structures for providing sensing signals indicative of a capacitive coupling between each sensing structure and said finger in response to a change in potential difference between a finger potential of said finger and a sensing structure potential of said sensing structure, said read-out circuitry being connected to each of said sensing structures in such a way that said sensing structure potential follows a sensing reference potential of said sensing arrangement; and
sensing reference potential providing circuitry connected to said sensing arrangement for providing, to said sensing arrangement, said sensing reference potential in the form of a sensing reference signal alternating, in relation to said device reference potential, between a first sensing reference potential and a second sensing reference potential, a change in potential difference, in relation to said device reference potential, between said first sensing reference potential and said second sensing reference potential resulting in said change in potential difference between said finger potential and said sensing structure potential, wherein said sensing reference potential providing circuitry includes;
a first capacitor;
a second capacitor;
charging circuitry for charging said first capacitor and said second capacitor; and
switching circuitry connected to said first capacitor, said second capacitor, said charging circuitry, and said sensing arrangement for alternatingly switching said sensing reference potential providing circuitry between;
a first state in which said first capacitor and said second capacitor are connected in parallel to said charging circuitry to allow said charging circuitry to charge said first capacitor and said second capacitor, and said sensing reference potential providing circuitry provides said first sensing reference potential to said sensing arrangement; and
a second state in which said first capacitor and said second capacitor are disconnected from said charging circuitry and connected in series between said device reference potential input and said sensing arrangement, whereby said sensing reference potential providing circuitry provides said second sensing reference potential to said sensing arrangement.
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Accused Products
Abstract
A fingerprint sensing system comprising a device connection interface including a device reference potential input, a sensing arrangement, and sensing reference potential providing circuitry. The sensing arrangement includes multiple sensing structures and read-out circuitry connected to each of the sensing structures. The sensing reference potential providing circuitry provides a sensing reference potential to the sensing arrangement in the form of a sensing reference signal alternating between a first sensing reference potential and a second sensing reference potential, and comprises a first capacitor; a second capacitor; charging circuitry; and switching circuitry for alternatingly switching the sensing reference potential providing circuitry between a first state in which the first capacitor and the second capacitor are connected in parallel to the charging circuitry; and a second state in which the first capacitor and the second capacitor, when charged, are connected in series between the device reference potential input and the sensing arrangement.
12 Citations
15 Claims
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1. A fingerprint sensing system for sensing a fingerprint pattern of a finger, said fingerprint sensing system comprising:
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a device connection interface for connection of said fingerprint sensing system to an electronic device, said device connection interface including a device reference potential input for receiving a device reference potential from said electronic device; a sensing arrangement including; a plurality of sensing structures, each being covered by a dielectric structure; and read-out circuitry connected to each of said sensing structures for providing sensing signals indicative of a capacitive coupling between each sensing structure and said finger in response to a change in potential difference between a finger potential of said finger and a sensing structure potential of said sensing structure, said read-out circuitry being connected to each of said sensing structures in such a way that said sensing structure potential follows a sensing reference potential of said sensing arrangement; and sensing reference potential providing circuitry connected to said sensing arrangement for providing, to said sensing arrangement, said sensing reference potential in the form of a sensing reference signal alternating, in relation to said device reference potential, between a first sensing reference potential and a second sensing reference potential, a change in potential difference, in relation to said device reference potential, between said first sensing reference potential and said second sensing reference potential resulting in said change in potential difference between said finger potential and said sensing structure potential, wherein said sensing reference potential providing circuitry includes; a first capacitor; a second capacitor; charging circuitry for charging said first capacitor and said second capacitor; and switching circuitry connected to said first capacitor, said second capacitor, said charging circuitry, and said sensing arrangement for alternatingly switching said sensing reference potential providing circuitry between; a first state in which said first capacitor and said second capacitor are connected in parallel to said charging circuitry to allow said charging circuitry to charge said first capacitor and said second capacitor, and said sensing reference potential providing circuitry provides said first sensing reference potential to said sensing arrangement; and a second state in which said first capacitor and said second capacitor are disconnected from said charging circuitry and connected in series between said device reference potential input and said sensing arrangement, whereby said sensing reference potential providing circuitry provides said second sensing reference potential to said sensing arrangement. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of sensing a fingerprint pattern of a finger using a fingerprint sensing system comprising:
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a device connection interface for connection of said fingerprint sensing system to an electronic device, said device connection interface including a device reference potential input for receiving a device reference potential from said electronic device; a sensing arrangement including; a plurality of sensing structures, each being covered by a dielectric structure and being arranged to capacitively couple to said finger when said finger is placed on said dielectric structure; and read-out circuitry connected to each of said sensing structures in such a way that said sensing structure potential follows a sensing reference potential of said sensing arrangement; and sensing reference potential providing circuitry connected to said sensing arrangement for providing said sensing reference potential to said sensing arrangement, said sensing reference potential providing circuitry includes a first capacitor; and
a second capacitor,said method comprising the steps of; a) connecting said first capacitor and said second capacitor in parallel; b) charging said first capacitor and said second capacitor while said first capacitor and said second capacitor are connected in parallel; c) providing, while charging said first capacitor and said second capacitor, a first sensing reference potential to said sensing arrangement; d) sensing, by said read-out circuitry, a first charge carried by at least one of said sensing structures while said first sensing reference potential is provided to said sensing arrangement; e) connecting said charged first capacitor and said charged second capacitor in series between said device reference potential input and said sensing arrangement to change said sensing reference potential, in relation to said device reference potential, from said first sensing reference potential to a second sensing reference potential; f) sensing, by said read-out circuitry, a second charge carried by at least one of said sensing structures while said second sensing reference potential is provided to said sensing arrangement; and g) forming, by said read-out circuitry, a sensing signal for said at least one sensing structure indicative of a difference between said first charge and said second charge, wherein steps a) to g) are repeated until said sensing signal has been formed for each of said sensing structures. - View Dependent Claims (15)
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Specification