Modulation scheme for fingerprint sensing
First Claim
1. A processing system, comprising:
- a fingerprint sensor, comprising;
a plurality of sensor electrodes,a plurality of receivers coupled to the sensor electrodes,a DC power source, anda modulator; and
a reference voltage rail configured to power the fingerprint sensor, wherein the receivers are configured to acquire resulting signals from the sensor electrodes for capacitive sensing while the reference voltage rail is modulated by the modulator,wherein the DC power source is coupled to the reference voltage rail,wherein the modulator includes modulation circuitry and coupling circuitry, the coupling circuitry comprising a switched capacitor network configured to selectively connect and disconnect a capacitor to the DC power source, wherein when the capacitor is connected to the DC power source, the DC power source charges the capacitor, and when disconnected from the DC power source, charge stored on the capacitor maintains a reference voltage provided to the modulation circuitry.
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Accused Products
Abstract
This disclosure generally provides a fingerprint sensor that derives a fingerprint by measuring capacitive sensing signals while modulating a reference voltage rail used to power the fingerprint sensor. In one embodiment, the fingerprint sensor is integrated into an electronic device which may include other components such as a display, I/O devices, speakers, and the like. To power these components, the electronic device may include a DC power supply which outputs reference voltages. When transmitting the reference voltages to the fingerprint sensor, the electronic device may modulate the voltages using a modulating signal. Because the reference voltages are used to power the components in the fingerprint sensor, modulating the rail voltages also causes the components coupled to the reference voltages to also modulate. While this modulation occurs, the fingerprint sensor measures resulting signals using a plurality of sensor electrodes which are then processed to derive a fingerprint.
250 Citations
21 Claims
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1. A processing system, comprising:
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a fingerprint sensor, comprising; a plurality of sensor electrodes, a plurality of receivers coupled to the sensor electrodes, a DC power source, and a modulator; and a reference voltage rail configured to power the fingerprint sensor, wherein the receivers are configured to acquire resulting signals from the sensor electrodes for capacitive sensing while the reference voltage rail is modulated by the modulator, wherein the DC power source is coupled to the reference voltage rail, wherein the modulator includes modulation circuitry and coupling circuitry, the coupling circuitry comprising a switched capacitor network configured to selectively connect and disconnect a capacitor to the DC power source, wherein when the capacitor is connected to the DC power source, the DC power source charges the capacitor, and when disconnected from the DC power source, charge stored on the capacitor maintains a reference voltage provided to the modulation circuitry. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An input device, comprising:
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a DC power source a fingerprint sensor comprising; a plurality of sensor electrodes, a plurality of receivers coupled to the sensor electrodes, and a modulator; a reference voltage rail configured to power the fingerprint sensor, wherein the receivers are configured to acquire resulting signals from the sensor electrodes for capacitive sensing while the reference voltage rail is modulated by the modulator, and wherein the DC power source is coupled to the reference voltage rail; and a chassis containing the fingerprint sensor, wherein the reference voltage rail is modulated relative to a chassis ground by the modulator, wherein the modulator includes modulation circuitry and coupling circuitry, the coupling circuitry comprising a switched capacitor network configured to selectively connect and disconnect a capacitor to the DC power source, wherein when the capacitor is connected to the DC power source, the DC power source charges the capacitor, and when disconnected from the DC power source, charge stored on the capacitor maintains a reference voltage provided to the modulation circuitry. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A method comprising:
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connecting a capacitor in a switched capacitor network to a DC power source to charge the capacitor; disconnecting the capacitor from the DC power source, wherein charge stored on the capacitor maintains reference voltages provided to modulation circuitry in a modulator when the capacitor is disconnected from the DC power source; modulating, using the modulation circuitry, a reference voltage rail used to provide power to a fingerprint sensor; and acquiring, while modulating the reference voltage rail, first resulting signals from a plurality of sensor electrodes at a plurality of receivers for performing capacitive sensing, wherein the sensor electrodes are disposed in the fingerprint sensor. - View Dependent Claims (18, 19, 20, 21)
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Specification