Capacitive sensing array modulation
First Claim
1. An electronic device, comprising:
- a fingerprint sensor comprising;
a sensor pad;
a dielectric positioned above the sensor pad; and
an electrically conductive ring surrounding the sensor pad and the dielectric, the electrically conductive ring at least partially elevated with respect to the sensor pad and the dielectric;
a modulating circuit electrically connected to the fingerprint sensor and configured to maintain the electrically conductive ring at a constant voltage having an absolute value less than four volts relative to a system ground, the modulating circuit configured to;
provide a first modulated voltage to the sensor pad; and
provide a second modulated voltage to the sensor pad, the second modulated voltage lower than the first modulated voltage and greater than the system ground;
wherein;
a relative voltage difference between the first modulated voltage and the second modulated voltage is received by the sensor pad as a sensor pad supply voltage.
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Abstract
A capacitive fingerprint sensor that may be formed of an array of sensing elements. Each capacitive sensing element of the array may register a voltage that varies with the capacitance of a capacitive coupling. A finger may capacitively couple to the individual capacitive sensing elements of the sensor, such that the sensor may sense a capacitance between each capacitive sensing element and the flesh of the fingerprint. The capacitance signal may be detected by sensing the change in voltage on the capacitive sensing element as the relative voltage between the finger and the sensing chip is changed. Alternately, the capacitance signal may be detected by sensing the change in charge received by the capacitive sensing elements as the relative voltage between the finger and the sensing chip is changed.
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Citations
19 Claims
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1. An electronic device, comprising:
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a fingerprint sensor comprising; a sensor pad; a dielectric positioned above the sensor pad; and an electrically conductive ring surrounding the sensor pad and the dielectric, the electrically conductive ring at least partially elevated with respect to the sensor pad and the dielectric; a modulating circuit electrically connected to the fingerprint sensor and configured to maintain the electrically conductive ring at a constant voltage having an absolute value less than four volts relative to a system ground, the modulating circuit configured to; provide a first modulated voltage to the sensor pad; and provide a second modulated voltage to the sensor pad, the second modulated voltage lower than the first modulated voltage and greater than the system ground;
wherein;a relative voltage difference between the first modulated voltage and the second modulated voltage is received by the sensor pad as a sensor pad supply voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A fingerprint sensing system, comprising:
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a sensor pad; a dielectric positioned over the sensor pad; an electrically conductive ring surrounding the sensor pad and the dielectric, wherein at least a portion of the electrically conductive ring is elevated with respect to the dielectric and the sensor pad such that the elevated portion of the electrically conductive ring is configured for contact by a finger; and a modulating circuit operably connected to the sensor pad and the electrically conductive ring, the modulating circuit adapted to maintain the electrically conductive ring at a substantially constant system ground voltage level and to provide to the sensor pad; a first modulated voltage greater than the system ground voltage level; and a second modulated voltage less than the first modulated voltage and greater than the system ground voltage level;
whereina direct current voltage difference between the first modulated voltage and the second modulated voltage is received by the sensor pad as a sensor pad supply voltage; and the second modulated voltage is received by the sensor pad as a sensor pad ground voltage level. - View Dependent Claims (11, 12, 13, 14, 15)
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16. A method for operating a fingerprint sensor comprising a sensor pad, a dielectric positioned above the sensor pad, and an elevated electrically conductive ring adjacent to and surrounding the dielectric, the method comprising:
when a finger is in contact with the dielectric and the electrically conductive ring; applying, by the sensor pad, a first modulated signal to at least one capacitive sensing element of the sensor pad when a voltage supply received by the sensor pad is in a low state and the electrically conductive ring is held at a system ground; obtaining, by the sensor pad, a first sense signal from the at least one capacitive sensing when the voltage supply received by the sensor pad is in the low voltage state and the electrically conductive ring is held at a system ground; applying, by the sensor pad, a second modulated signal to the at least one capacitive sensing element of the sensor pad when the voltage supply received by the sensor pad is in a high state and the electrically conductive ring is held at a system ground; obtaining, by the sensor pad, a second sense signal from the at least one capacitive sensing element when the voltage supply received by the sensor pad is in the high voltage state and the electrically conductive ring is held at the system ground; and constructing an image of a portion of the finger based, at least in part, on the first sense signal and second sense signal. - View Dependent Claims (17, 18, 19)
Specification