METHOD AND APPARATUS FOR SENSING CAPACITANCE VALUE AND CONVERTING IT INTO DIGITAL FORMAT
First Claim
1. A capacitance sensing device comprising:
- a signal generator that generates both a digital local oscillator (LO) signal and an excitation signal;
a capacitance-to-amplitude converter (C2A) coupled to the signal generator, the C2A converts a measured capacitance to an AC signal having an amplitude proportional to the measured capacitance;
a demodulator coupled to receive the AC signal from the C2A and the digital LO signal from the signal generator, the demodulator multiplies the AC signal with the digital LO signal to generate a DC signal proportional to the amplitude; and
an analog-to-digital converter (ADC) coupled to the output of the demodulator, the ADC outputs a digital conversion value proportional to both the DC component and the measured capacitance.
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Abstract
A capacitive sensing system are configured to sense a capacitance value and convert the sensed capacitance value to a digital format. The capacitive sensing system provides good selectivity and immunity to noise and interference, which can be further enhanced by enabling spread spectrum excitation. In some embodiments, the capacitive sensing system utilizes a sinusoidal excitation signal that results in low electromagnetic emissions, limited to narrow frequency band. In some embodiments, the capacitive sensing system is configured to operate in a spread spectrum mode, in which the majority of the excitation signal power is carried in the assigned bandwidth. The excitation frequency and the bandwidth of the spread spectrum excitation signal are programmable in a wide range, which allows for avoiding frequency conflicts in the operating environment.
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Citations
20 Claims
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1. A capacitance sensing device comprising:
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a signal generator that generates both a digital local oscillator (LO) signal and an excitation signal; a capacitance-to-amplitude converter (C2A) coupled to the signal generator, the C2A converts a measured capacitance to an AC signal having an amplitude proportional to the measured capacitance; a demodulator coupled to receive the AC signal from the C2A and the digital LO signal from the signal generator, the demodulator multiplies the AC signal with the digital LO signal to generate a DC signal proportional to the amplitude; and an analog-to-digital converter (ADC) coupled to the output of the demodulator, the ADC outputs a digital conversion value proportional to both the DC component and the measured capacitance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of converting a measured capacitance, the method comprising:
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measuring a capacitance; generating a digital local oscillator (LO) signal and an excitation signal; converting the measured capacitance according to the excitation signal to an AC signal having an amplitude proportional to the measured capacitance; multiplying the AC signal with the digital LO signal to form a demodulated signal with a DC component proportional to amplitude; and converting the demodulated signal to a digital conversion value that is proportional to both the DC component and the measured capacitance. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification