CONTINUOUS TIME CORRELATOR ARCHITECTURE
First Claim
Patent Images
1. A capacitance measurement circuit comprising:
- a. an external capacitor; and
b. a coherent detection circuit coupled to the external capacitor and configured to measure a capacitance of the external capacitor and to convert the measured capacitance to a corresponding voltage output, wherein the coherent detection circuit comprises a programmable impedance element, a first amplifier coupled to an output of the programmable impedance element, and an integrating feedback capacitor coupled to an input of the first amplifier and to an output of the first amplifier.
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Abstract
An analog front end circuit utilizes coherent detection within a capacitance measurement application. The analog front end circuit uses coherent detection to measure capacitance of a touch screen display. An analog excitation signal is modulated by a capacitor to be measured. The modulated signal is synchronously demodulated using a correlator, which includes an integrated mixing and integration circuit. The correlator includes a programmable impedance element that generates a time-varying conductance according to a controlling digitized waveform.
38 Citations
26 Claims
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1. A capacitance measurement circuit comprising:
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a. an external capacitor; and b. a coherent detection circuit coupled to the external capacitor and configured to measure a capacitance of the external capacitor and to convert the measured capacitance to a corresponding voltage output, wherein the coherent detection circuit comprises a programmable impedance element, a first amplifier coupled to an output of the programmable impedance element, and an integrating feedback capacitor coupled to an input of the first amplifier and to an output of the first amplifier. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15)
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11. The capacitance measurement circuit of claim 11 wherein the period of time is a multiple of 1/f, where f is a frequency of the analog excitation signal.
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16. A capacitance measurement circuit comprising:
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a. a signal generator configured to generate an analog excitation signal; b. a touch screen display having at least one capacitor, wherein the capacitor is configured to input the analog excitation signal and to output a modulated analog excitation signal, wherein the analog excitation signal is modulated according to a capacitance of the capacitor; c. a first amplifier coupled to the capacitor and a first feedback capacitor coupled to an input and to an output of the first amplifier, wherein the first amplifier is configured to input the modulated analog excitation signal and to output an amplified modulated analog excitation signal; d. a programmable impedance element coupled to the first amplifier, wherein the programmable impedance element is configured to input the amplified modulated analog excitation signal and to output a mixed analog signal, further wherein the programmable impedance element is programmed with a time-varying conductance according to a programmed waveform such that the mixed analog signal output from the programmable impedance element is a product of the modulated signal and the programmed waveform; and e. a second amplifier coupled to the programmable impedance element and a second feedback capacitor coupled to an input and to an output of the second amplifier, wherein the second amplifier and the second feedback capacitor are configured to receive the mixed analog signal and to integrate the mixed analog signal over a discrete period of time to output a voltage signal, wherein the voltage signal corresponds to the capacitance of the capacitor.
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17. An integrated mixing and integration circuit comprising:
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a. a programmable impedance element configured to receive as input a modulated signal, wherein the programmable impedance element is programmed with a time-varying conductance according to a programmed waveform such that a signal output from the programmable impedance element is a multiple of the modulated signal and the programmed waveform; b. an amplifier coupled to an output of the programmable impedance element; and c. an integrating feedback capacitor coupled to an input of the amplifier and to an output of the amplifier. - View Dependent Claims (18, 19, 20, 21, 22)
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23. A method of measuring capacitance, the method comprising:
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a. generating an analog excitation signal; b. applying the analog excitation signal to a capacitor to be measured, thereby modulating the analog excitation signal; c. generating a time-varying conductance according to a digitized waveform, wherein the time-varying conductance is correlated to the analog excitation signal; d. applying the time-varying conductance to the modulated analog excitation signal, thereby generating a mixed signal; and e. integrating the mixed signal over a discrete period of time thereby demodulating the modulated analog excitation signal resulting in an output voltage corresponding to a capacitance of the capacitor. - View Dependent Claims (24, 25, 26)
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Specification