Signal processing for a capacitive sensor system with robustness to noise
First Claim
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1. A capacitive sensor, comprising:
- a transmit electrode configured to provide an alternating electric field for the capacitive sensor;
an oscillator for generating a carrier signal;
one or more receive electrodes for detecting variations in the alternating electric field;
an adaptive frequency adjustment unit coupled with the oscillator and configured to adjust an operating frequency of the alternating electric field responsive to detection of a noise measure, anda modulator configured to modulate the carrier signal at the operating frequency depending on a sensed capacitance, wherein the modulated carrier signal is synchronously demodulated and downsampled.
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Abstract
A capacitive sensor includes a transmit electrode configured to provide an alternating electric field to a sensor; one or more receive electrodes for detecting variations in the alternating electric field; and an adaptive frequency adjustment unit configured to adjust an operating frequency of the alternating electric field responsive to detection of a noise measure, such as noise power.
8 Citations
28 Claims
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1. A capacitive sensor, comprising:
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a transmit electrode configured to provide an alternating electric field for the capacitive sensor; an oscillator for generating a carrier signal; one or more receive electrodes for detecting variations in the alternating electric field; an adaptive frequency adjustment unit coupled with the oscillator and configured to adjust an operating frequency of the alternating electric field responsive to detection of a noise measure, and a modulator configured to modulate the carrier signal at the operating frequency depending on a sensed capacitance, wherein the modulated carrier signal is synchronously demodulated and downsampled. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for providing noise robustness to a capacitive sensing system, comprising:
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generating a carrier signal and modulating the carrier signal at the operating frequency depending on a sensed capacitance; defining a plurality of potential operating transmit frequencies; determining a corresponding noise measure corresponding to each of the potential operating frequencies; operating the capacitive sensing system at one of the plurality of potential operating transmit frequencies; measuring an operating noise measure at the operating frequency; and selecting a new operating frequency responsive to a value of the measured operating noise measure; wherein the modulated carrier signal is synchronously demodulated and downsampled. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A capacitive sensor system, comprising:
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a transmit electrode configured to provide an alternating electric field to a capacitive sensor;
a plurality of reception electrodes associated with the transmit electrode for detecting variations in the alternating electric field generated by the transmit electrode; andan adaptive frequency adjustment unit configured to adjust an operating frequency of the alternating electric field in accordance with modeling the capacitive sensor system as an amplitude modulation system with direct sampling and synchronous demodulation. - View Dependent Claims (25, 26, 27, 28)
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Specification