Capacitance detection circuit that detects minute changes in capacitance
First Claim
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1. A capacitance-to-data converter (CDC) for use in a system identifying a change in the capacitance of the variable capacitor, the system including a frequency-domain capacitance extractor, the CDC comprising:
- a variable capacitance oscillator (VCO), including the variable capacitor, to generate a VCO oscillating signal with a frequency based on a VCO resonant frequency that is modulated based on changes in a capacitance of the variable capacitor;
frequency digitization circuitry to receive the VCO oscillating signal, and generate time-domain digital samples that represent a portion of the VCO oscillating signal, including modulation based on the changes in capacitance; and
a frequency decomposition module coupled to receive the time-domain digital samples generated by the frequency digitization circuitry, and;
to convert these time-domain digital samples from the time domain to the frequency domain by generating corresponding frequency-domain information for each of these time-domain digital samples as a predetermined number of frequencies and frequency magnitudes;
to output corresponding frequency-domain information for input to the frequency-domain capacitance extractor, the frequency-domain capacitance extractor having multiple predefined frequencies, and operable to determine for each predefined frequency, an extracted magnitude based on the frequency-domain information for that time-domain digital sample, the extracted magnitudes for the predefined frequencies corresponding to a change in the capacitance of the variable capacitor.
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Abstract
A capacitance detection circuit detects changes in the capacitance of a variable capacitor by using the change in capacitance to change the resonant frequency of a variable capacitor oscillator. The resonant frequency of the variable capacitor oscillator is converted from the time domain to the frequency domain, and then selected frequencies values are compared to known frequency domain values to detect the magnitude of the change in capacitance.
6 Citations
18 Claims
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1. A capacitance-to-data converter (CDC) for use in a system identifying a change in the capacitance of the variable capacitor, the system including a frequency-domain capacitance extractor, the CDC comprising:
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a variable capacitance oscillator (VCO), including the variable capacitor, to generate a VCO oscillating signal with a frequency based on a VCO resonant frequency that is modulated based on changes in a capacitance of the variable capacitor; frequency digitization circuitry to receive the VCO oscillating signal, and generate time-domain digital samples that represent a portion of the VCO oscillating signal, including modulation based on the changes in capacitance; and a frequency decomposition module coupled to receive the time-domain digital samples generated by the frequency digitization circuitry, and; to convert these time-domain digital samples from the time domain to the frequency domain by generating corresponding frequency-domain information for each of these time-domain digital samples as a predetermined number of frequencies and frequency magnitudes; to output corresponding frequency-domain information for input to the frequency-domain capacitance extractor, the frequency-domain capacitance extractor having multiple predefined frequencies, and operable to determine for each predefined frequency, an extracted magnitude based on the frequency-domain information for that time-domain digital sample, the extracted magnitudes for the predefined frequencies corresponding to a change in the capacitance of the variable capacitor. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A capacitance detection system comprising:
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a capacitance-to-data converter (CDC), including; a variable capacitance oscillator (VCO), including a variable capacitor, to generate a VCO oscillating signal with a frequency based on a VCO resonant frequency that is modulated based on changes in a capacitance of the variable capacitor, and frequency digitization circuitry to receive the VCO signal, and generate time-domain digital samples that represent a portion of the VCO signal, including modulation based on changes in capacitance; a frequency decomposition module coupled to receive time-domain digital samples generated by the frequency digitization circuitry, and to convert these time-domain digital samples from the time domain to the frequency domain by generating corresponding frequency-domain information for each of these time-domain digital samples as a corresponding number of frequencies and frequency magnitudes; and a frequency-domain capacitance extractor coupled to receive from the frequency decomposition module the frequency-domain information for respective time-domain digital samples, the frequency-domain capacitance extractor operable to to determine, for each predefined frequency, an extracted magnitude based on the frequency-domain information for that time-domain digital sample, the extracted magnitudes for the predefined frequencies corresponding to a change in the capacitance of the variable capacitor; to extract from the associated extracted magnitudes a change-in-capacitance value identifying a change in the capacitance of the variable capacitor in the VCO; and to output the change-in-capacitance value as representing a change in the capacitance of the variable capacitor in the VCO based on the frequency-domain information for the associated time-domain digital sample. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A method suitable for detecting capacitance changes with a variable capacitance oscillator (VCO) including a variable capacitor, comprising:
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generating, a VCO oscillating signal based on a VCO resonant frequency that is modulated based on changes in a capacitance of the variable capacitor; generating time-domain digital samples that represent a portion of the VCO oscillating signal including modulation based on changes in capacitance; and converting these time-domain digital samples from the time domain to the frequency domain by generating corresponding frequency-domain information for each of these time-domain digital samples as a corresponding a number of frequencies and frequency magnitudes; and extracting capacitance by, for each time-domain digital sample, determining an extracted magnitude based on the frequency-domain information for that time-domain digital sample, the extracted magnitudes for the predefined frequencies corresponding to a change in the capacitance of the variable capacitor; extracting from the associated extracted magnitudes a change-in-capacitance value identifying a change in the capacitance of the variable capacitor in the VCO; and outputting the change-in-capacitance value as representing a change in the capacitance of the variable capacitor in the VCO based on the frequency-domain information for the associated time-domain digital sample. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification