Apparatus and method for reducing parasitic capacitive coupling and noise in fingerprint sensing circuits
First Claim
1. A fingerprint sensing circuit for reducing parasitic capacitive coupling and noise when scanning a fingerprint, the fingerprint sensing circuit comprising:
- a plurality of transmitting elements configured to sequentially transmit a probing signal;
a digital ground to provide a ground for digital components in the fingerprint sensing circuit;
a quiet ground, different from the digital ground;
a grounding switch electrically connected between the quiet ground and a respective transmitting element; and
control logic configured to selectively connect each transmitting element to the quiet ground through the operation of the respective grounding switch.
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Accused Products
Abstract
A fingerprint sensing circuit for reducing noise and parasitic capacitive coupling is disclosed in one embodiment of the invention as including a plurality of transmitting elements to sequentially emit a probing signal. A digital ground is provided to ground digital components in the fingerprint sensing circuit. A quiet ground, separate from and quieter than the digital ground, is provided to ground transmitting elements that are not transmitting the probing signal. Similarly, control logic is provided to connect, to the quiet ground, transmitting elements that are not transmitting the probing signal, while disconnecting, from the quiet ground, transmitting elements that are emitting the probing signal. The quiet ground helps to reduce the adverse effects of parasitic capacitive coupling and noise on the inactive transmitting elements.
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Citations
29 Claims
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1. A fingerprint sensing circuit for reducing parasitic capacitive coupling and noise when scanning a fingerprint, the fingerprint sensing circuit comprising:
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a plurality of transmitting elements configured to sequentially transmit a probing signal; a digital ground to provide a ground for digital components in the fingerprint sensing circuit; a quiet ground, different from the digital ground; a grounding switch electrically connected between the quiet ground and a respective transmitting element; and control logic configured to selectively connect each transmitting element to the quiet ground through the operation of the respective grounding switch. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for reducing parasitic capacitive coupling and noise in a fingerprint sensing circuit, the method comprising:
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providing a plurality of transmitting elements to sequentially transmit a probing signal; providing a digital ground to ground digital components in the fingerprint sensing circuit; providing a quiet ground, different from the digital ground; providing a grounding switch electrically connected between the quiet ground and a respective transmitting element; selectively connecting, to the quiet ground, each transmitting element through the operation of the respective grounding switch; and disconnecting, from the quiet ground, transmitting elements that are transmitting the probing signal. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A fingerprint sensing circuit for reducing parasitic capacitive coupling and noise when scanning a fingerprint, the fingerprint sensing circuit comprising:
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a plurality of receiving elements configured to sequentially sense a probing signal; a digital ground configured to provide a ground for digital components in the fingerprint sensing circuit; a quiet ground, substantially separate from the digital ground, configured to provide a ground for selected receiving elements that are not currently sensing the probing signal; a grounding switch electrically connected between the quiet ground and a respective receiving element; and control logic configured to selectively disconnect a receiving element that is currently sensing the probing signal from the quiet ground, while selectively connecting receiving elements that are not sensing the probing signal to the quiet ground. - View Dependent Claims (16, 17, 18, 19, 20)
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21. A biometric sensing circuit comprising:
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a plurality of probe signal transmitting elements; a plurality of response signal receiving elements; a digital ground connected to digital components in the fingerprint sensing circuit; a quiet ground, substantially separate from the digital ground; a respective grounding switch electrically connected between the quiet ground and a respective transmitting element or the quiet ground and a respective response signal receiving element; and control logic configured to selectively connect at least one of each respective transmitting element to the quiet ground through the operation of the respective grounding switch and each respective response signal receiving element to the quiet ground through the operation of the respective grounding switch. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29)
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Specification