Capacitive fingerprint sensing device with demodulation circuitry in sensing element
First Claim
1. A capacitive fingerprint sensing system for sensing a fingerprint pattern of a finger, said capacitive fingerprint sensing system comprising:
- excitation signal providing circuitry for providing an excitation signal exhibiting a time-varying excitation potential including recurring changes from a first potential to a second potential and back to the first potential, in relation to a potential of said finger;
a plurality of sensing elements, each including;
a protective dielectric top layer to be touched by said finger;
an electrically conductive sensing structure arranged underneath said top layer, said sensing structure being coupled to said excitation signal providing circuitry to exhibit a time-varying sensing structure potential substantially following said excitation potential, wherein each of said changes of the excitation potential from said first potential to said second potential results in a change in potential difference between said finger and said sensing structure;
sensing circuitry connected to said sensing structure for providing a sensing signal indicative of a change of a charge carried by said sensing structure resulting from said change in potential difference between said finger and said sensing structure; and
demodulation circuitry connected to said sensing circuitry for combining said sensing signal and a demodulation signal being timing-related to said excitation signal to provide a combined signal including a DC signal component indicating said change of the charge carried by said sensing structure; and
readout circuitry connected to each of said sensing elements for providing a representation of said fingerprint pattern based on said DC signal component from each of said sensing elements.
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Abstract
A capacitive fingerprint sensing system includes excitation signal providing circuitry and a plurality of sensing elements. Each sensing element includes a protective dielectric top layer, an electrically conductive sensing structure coupled to the excitation signal for providing a sensing signal indicative of a change of a charge carried by the sensing structure resulting from a change in potential difference between the finger and the sensing structure, and demodulation circuitry connected to the sensing circuitry for combining the sensing signal and a demodulation signal being timing-related to the excitation signal to provide a combined signal including a DC signal component indicating the change of the charge carried by the sensing structure. The fingerprint sensing system further includes readout circuitry connected to each of the sensing elements for providing a representation of the fingerprint pattern based on the DC signal component from each of the sensing elements.
8 Citations
15 Claims
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1. A capacitive fingerprint sensing system for sensing a fingerprint pattern of a finger, said capacitive fingerprint sensing system comprising:
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excitation signal providing circuitry for providing an excitation signal exhibiting a time-varying excitation potential including recurring changes from a first potential to a second potential and back to the first potential, in relation to a potential of said finger; a plurality of sensing elements, each including; a protective dielectric top layer to be touched by said finger; an electrically conductive sensing structure arranged underneath said top layer, said sensing structure being coupled to said excitation signal providing circuitry to exhibit a time-varying sensing structure potential substantially following said excitation potential, wherein each of said changes of the excitation potential from said first potential to said second potential results in a change in potential difference between said finger and said sensing structure; sensing circuitry connected to said sensing structure for providing a sensing signal indicative of a change of a charge carried by said sensing structure resulting from said change in potential difference between said finger and said sensing structure; and demodulation circuitry connected to said sensing circuitry for combining said sensing signal and a demodulation signal being timing-related to said excitation signal to provide a combined signal including a DC signal component indicating said change of the charge carried by said sensing structure; and readout circuitry connected to each of said sensing elements for providing a representation of said fingerprint pattern based on said DC signal component from each of said sensing elements. - 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 capacitive fingerprint sensing system comprising excitation signal providing circuitry;
- and a plurality of sensing elements, each including;
a protective dielectric top layer to be touched by said finger; an electrically conductive sensing structure arranged underneath said top layer; and sensing circuitry connected to said sensing structure for providing a sensing signal indicative of a change of a charge carried by said sensing structure resulting from a change in potential difference between said finger and said sensing structure, wherein said method comprises the steps of; providing, using said excitation signal providing circuitry, an excitation signal to at least one of said finger and said sensing structure, to provide a time-varying potential difference between said finger and said sensing structure; providing, by said fingerprint sensing system, a demodulation signal being timing-related to said excitation signal; combining, by said fingerprint sensing system, said demodulation signal and said sensing signal to provide a combined signal including a DC signal component indicating said change of the charge carried by said sensing structure; and providing, using readout circuitry external to said sensing elements, a representation of said fingerprint pattern based on said DC signal component from each of said sensing elements. - View Dependent Claims (15)
- and a plurality of sensing elements, each including;
Specification