Adaptive Capacitive Sensing
First Claim
1. A sensing apparatus comprising:
- a first load component configured to couple to an interface device having a specific electrical characteristic, wherein the first load component and the specific electrical characteristic of the interface device together form a first load;
a sensing signal-path comprising the first load component, wherein the sensing signal-path is configured to be driven by a periodic control signal having a specific frequency to obtain an input signal;
a reference signal-path comprising a second load that forms a pole commensurate with a pole formed by the first load, wherein the reference signal-path is configured to be driven by the control signal to obtain a reference signal;
a mixer configured to;
generate a difference signal representative of a difference of the input signal and the reference signal; and
correlate the difference signal to the control signal to obtain a main output signal;
wherein the main output signal is indicative of a change in value of the specific electrical characteristic of the interface device.
1 Assignment
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Accused Products
Abstract
A capacitive sensing circuit may comprise an RC (resistive-capacitive) bridge circuit, with a switching signal simultaneously applied to a reference path, and a signal path comprising the capacitance to be detected. Small perturbations in the capacitance may be detected by mixing/correlating a difference signal representative of the difference between the reference path signal and the signal path signal, to the switching signal. The output of the mixer may be filtered to virtually eliminate all EMI signals. A narrowband approach may also allow filtering of unwanted signals, enabling operation in systems susceptible to high levels of noise. Frequency stepping of the switching signal may minimize inband signal interference, and allow operation in the presence of many signals that would otherwise result in failure of the sensing circuit. Pad calibration may be implemented to free the user from a need to characterize each button channel capacitance and tailor the operation for each channel.
102 Citations
36 Claims
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1. A sensing apparatus comprising:
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a first load component configured to couple to an interface device having a specific electrical characteristic, wherein the first load component and the specific electrical characteristic of the interface device together form a first load; a sensing signal-path comprising the first load component, wherein the sensing signal-path is configured to be driven by a periodic control signal having a specific frequency to obtain an input signal; a reference signal-path comprising a second load that forms a pole commensurate with a pole formed by the first load, wherein the reference signal-path is configured to be driven by the control signal to obtain a reference signal; a mixer configured to; generate a difference signal representative of a difference of the input signal and the reference signal; and correlate the difference signal to the control signal to obtain a main output signal; wherein the main output signal is indicative of a change in value of the specific electrical characteristic of the interface device. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method comprising:
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driving a signal sensing-path with a periodic control signal having a specific frequency to generate an input signal, wherein the signal sensing-path comprises an interface device having a specific electrical characteristic; driving a reference sensing-path with the control signal to generate a reference signal; generating a difference signal representative of a difference of the input signal and the reference signal; and correlating the difference signal to the control signal to generate a main output signal, wherein the output signal is indicative of a change in value of the specific electrical characteristic of the interface device. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
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32. A circuit comprising:
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a sensing signal-path comprising a first resistor configured to couple to a button pad having a parasitic capacitance that changes when an object is brought within at least a specified distance of the button pad; a reference signal-path comprising a second resistor coupled to a first capacitor; an oscillator configured to; generate a switching signal having a specific frequency; apply the switching signal to the sensing signal-path to obtain an input signal; apply the switching signal to the reference signal-path to obtain a reference signal; and a mixer configured to; generate a difference signal representative of a difference of the input signal and the reference signal; and correlate the difference signal to the switching signal to obtain a main output signal; wherein the main output signal is indicative of a change in the parasitic capacitance of the button pad. - View Dependent Claims (33, 34, 35, 36)
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Specification