Capacitive touch sense architecture having a correlator for demodulating a measured capacitance from an excitation signal
First Claim
Patent Images
1. A capacitance measurement circuit comprising:
- an external capacitor; and
a coherent detection circuit coupled to the external capacitor and configured to measure a capacitance of the external capacitor, the coherent detection circuit including a signal generator coupled to the external capacitor, a mixing circuit and an integration circuit, wherein;
the signal generator is configured to generate an analog excitation signal having a first frequency “
f”
;
a modulated analog excitation signal, being the analog excitation signal modulated by a capacitance of the external capacitor, is input to a first input of the mixing circuit;
the analog excitation signal is input to a second input of the mixing circuit, the mixing circuit being configured to multiply the modulated analog excitation signal and the analog excitation signal and to output a mixed analog signal, the mixed analog signal including a DC voltage term plus a sine term having a second frequency approximately 2 f; and
the integration circuit filters out noise by providing a band-pass filtering function with a peak around f and is configured to output a corresponding voltage output that is proportional to a capacitance value of the capacitance.
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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 a discrete mixer and a discrete integrator. The excitation signal is also input to the mixer such that the modulated signal is multiplied by the excitation signal. The excitation signal is an analog signal having a sine wave function or other waveform.
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Citations
12 Claims
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1. A capacitance measurement circuit comprising:
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an external capacitor; and a coherent detection circuit coupled to the external capacitor and configured to measure a capacitance of the external capacitor, the coherent detection circuit including a signal generator coupled to the external capacitor, a mixing circuit and an integration circuit, wherein; the signal generator is configured to generate an analog excitation signal having a first frequency “
f”
;a modulated analog excitation signal, being the analog excitation signal modulated by a capacitance of the external capacitor, is input to a first input of the mixing circuit; the analog excitation signal is input to a second input of the mixing circuit, the mixing circuit being configured to multiply the modulated analog excitation signal and the analog excitation signal and to output a mixed analog signal, the mixed analog signal including a DC voltage term plus a sine term having a second frequency approximately 2 f; and the integration circuit filters out noise by providing a band-pass filtering function with a peak around f and is configured to output a corresponding voltage output that is proportional to a capacitance value of the capacitance. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A capacitance measurement circuit comprising:
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a signal generator configured to generate an analog excitation signal having a first frequency “
f”
;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; an amplifier coupled to the capacitor and a feedback capacitor coupled to an input and to an output of the amplifier, wherein the amplifier is configured to input the modulated analog excitation signal and to output an amplified modulated analog excitation signal; a mixing circuit coupled to the amplifier and to the signal generator, wherein the mixing circuit is configured to input the amplified modulated analog excitation signal and an analog correlation signal that is correlated to the analog excitation signal, and to output a mixed analog signal, the mixed analog signal including a DC voltage term plus a sine term having a second frequency approximately 2 f; and an integration circuit coupled to the mixing circuit, wherein the integration circuit filters out noise by providing a band-pass filtering function with a peak around f and is configured to receive the mixed analog signal and to output a voltage signal, wherein the voltage signal corresponds to the capacitance value of the capacitor.
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9. A method of measuring capacitance, the method comprising:
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generating an analog excitation signal having a first frequency “
f”
; andapplying the analog excitation signal to a capacitor to be measured, wherein; the analog excitation signal is modulated based upon a capacitance of the capacitor; and
multiplying, via a mixing circuit, the modulated analog excitation signal by the analog excitation signal to generate a mixed signal, the mixed signal including a DC voltage term plus a sine term having a second frequency approximately 2 f; and
integrating the mixed signal, via an integrating circuit that filters out noise by providing a band-pass filtering function with a peak around f, and is configured to generate an output voltage corresponding to the capacitance of the capacitor. - View Dependent Claims (10, 11, 12)
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Specification