Capacitive fingerprint sensing device with current readout from sensing elements
First Claim
1. 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 including;
a protective dielectric top layer to be touched by said finger;
an electrically conductive sensing structure arranged underneath said top layer;
a charge amplifier connected to said sensing structure for providing a sensing voltage signal indicative of a change of a charge carried by said sensing structure resulting from a change in a potential difference between said finger and said sensing structure, said charge amplifier comprising;
a first input connected to said sensing structure;
a second input;
an output for providing said sensing voltage signal;
a feedback capacitor connected between said first input and said output; and
at least one amplifier stage between said first and second inputs, and said output; and
a voltage-to-current converter for converting said sensing voltage signal to a sensing current signal indicative of said change of charge carried by said sensing structure,wherein said fingerprint sensing device further comprises readout circuitry connected to the voltage-to-current converter comprised in each of said sensing elements for receiving sensing current signals from said plurality of sensing elements and providing a representation of said fingerprint pattern based on said sensing current signals.
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Abstract
The present invention relates to a capacitive fingerprint sensing device comprising a plurality of sensing elements. Each sensing element includes a protective dielectric top layer to be touched by a finger; an electrically conductive sensing structure arranged underneath the top layer; a charge amplifier connected to the sensing structure for providing a sensing voltage signal indicative of a change of a charge carried by the sensing structure resulting from a change in a potential difference between the finger and the sensing structure; and a voltage-to-current converter for converting the sensing voltage signal to a sensing current signal indicative of the change of charge carried by the sensing structure. Hereby, accurate sensing as well as faster operation of the sensing elements can be achieved without a corresponding increase in power consumption.
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Citations
13 Claims
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1. A capacitive fingerprint sensing device for sensing a fingerprint pattern of a finger, said capacitive fingerprint sensing device comprising:
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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; a charge amplifier connected to said sensing structure for providing a sensing voltage signal indicative of a change of a charge carried by said sensing structure resulting from a change in a potential difference between said finger and said sensing structure, said charge amplifier comprising; a first input connected to said sensing structure; a second input; an output for providing said sensing voltage signal; a feedback capacitor connected between said first input and said output; and at least one amplifier stage between said first and second inputs, and said output; and a voltage-to-current converter for converting said sensing voltage signal to a sensing current signal indicative of said change of charge carried by said sensing structure, wherein said fingerprint sensing device further comprises readout circuitry connected to the voltage-to-current converter comprised in each of said sensing elements for receiving sensing current signals from said plurality of sensing elements and providing a representation of said fingerprint pattern based on said sensing current signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of sensing a fingerprint pattern of a finger using a capacitive fingerprint sensor comprising a plurality of sensing elements, each including:
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a protective dielectric top layer to be touched by said finger; an electrically conductive sensing structure arranged underneath said top layer; and a charge amplifier connected to said sensing structure for providing a sensing voltage signal indicative of a change of a charge carried by said sensing structure resulting from a change in a potential difference between said finger and said sensing structure, said charge amplifier comprising; a first input connected to said sensing structure; a second input; an output for providing said sensing voltage; a feedback capacitor connected between said first input and said output; and at least one amplifier stage between said first and second inputs, and said output, wherein said method comprises the steps of; changing said potential difference between said finger and said sensing structure; providing, by the charge amplifier, said sensing voltage; converting, in said sensing element, said sensing voltage to a sensing current; and receiving, using readout circuitry external to said sensing elements, sensing currents from each of said sensing elements and providing a representation of said fingerprint pattern based on said received sensing currents.
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Specification