Method and apparatus for detecting a change in capacitance of a capacitive proximity sensor
First Claim
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1. A method for detecting a change in capacitance of a capacitive sensing element having a nominal capacitance value, the method comprising:
- employing a single non-Contact capacitive sensing element;
coupling the sensing element to a first oscillator, said first oscillator generating a first frequency dependent upon the capacitance value of the sensing element; and
comparing said first frequency to a reference frequency, said reference frequency being a second frequency generated by a second oscillator;
wherein the change in capacitance from the nominal capacitance value is detected it said first frequency differs from said reference frequency by a determined frequency value.
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Abstract
A method for detecting a change in capacitance of a capacitive sensing element having a nominal capacitance value is disclosed. In an exemplary embodiment, the method includes coupling the sensing element to a first oscillator, the first oscillator generating a first frequency dependent upon the capacitance value of the sensing element. The first frequency is compared to a reference frequency generated by a second oscillator. The change in capacitance from the nominal capacitance value is detected if the first frequency differs from said reference frequency by a determined frequency value.
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16 Claims
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1. A method for detecting a change in capacitance of a capacitive sensing element having a nominal capacitance value, the method comprising:
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employing a single non-Contact capacitive sensing element;
coupling the sensing element to a first oscillator, said first oscillator generating a first frequency dependent upon the capacitance value of the sensing element; and
comparing said first frequency to a reference frequency, said reference frequency being a second frequency generated by a second oscillator;
wherein the change in capacitance from the nominal capacitance value is detected it said first frequency differs from said reference frequency by a determined frequency value. - View Dependent Claims (2, 3, 4, 5, 6)
configuring said first oscillator such that said first frequency and said reference frequency are offset from one another by a fixed offset value when the capacitance of said capacitive sensing element is equal to the nominal capacitance value.
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3. The method of claim 2, further comprising:
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inputting said first frequency and said reference frequency into a mixer; and
inputting an output of said mixer into a low pass filter;
wherein an output of said low pass filter is an intermediate frequency (IF), said intermediate frequency corresponding to the difference between said first frequency and said reference frequency.
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4. The method of claim 3, wherein said intermediate frequency (IF) is in the range of about 0.01 to about 15 MHz.
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5. The method of claim 4, wherein said first frequency and said reference frequency are at least 900 MHz.
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6. The method of claim 3, further comprising:
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transmitting said intermediate frequency to a control module; and
comparting said intermediate frequency to said fixed offset value;
said fixed offset value being stored with in said control module;
wherein an increase in capacitance from the nominal capacitance value is detected is said intermediate frequency exceeds said fixed offset value.
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7. An apparatus for detecting a change in capacitance of a single non-contact capacitive sensing element having a nominal capacitance value, comprising:
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a first oscillator coupled to the single non-contact capacitive sensing element, said first oscillator generating a first frequency dependent upon the capacitance value of the sensing element;
a second oscillator generating a reference frequency; and
a device for comparing said first frequency to said reference frequency;
wherein the change in capacitance from the nominal capacitance value is detected if said first frequency differs from said reference frequency by a determined frequency value. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15)
a mixer, said mixer having said first frequency as a first input thereto and said reference frequency as a second input thereto; and
a low pass filter, said low pass filter having an output of said mixer as an input thereto;
wherein an output of said low pass filter is an intermediate frequency (IF), said intermediate frequency corresponding to the difference between said first frequency and said reference frequency.
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10. The apparatus of claim 9, wherein said intermediate frequency (IF) is in the range of about 0.01 to about 15 MHz.
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11. The apparatus of claim 10, wherein said first frequency and said reference frequency are at least 900 MHz.
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12. The apparatus of claim 11, wherein siad fixed offset value is about 3 MHz.
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13. The apparatus of claim 9, further comprising:
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a control module;
a signal line for transmitting said intermediate frequency to said control module; and
said intermediate frequency being compared to said fixed offset value, said fixed offset value further being stored with in said control module;
wherein an increase in capacitance from the nominal capacitance value is detected if said intermediate frequency exceeds said fixed offset value.
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14. The apparatus of claim 13, further comprising:
a bias “
T”
arrangement, configured between said low pass filter and said signal line, said bias “
T”
arrangement enabling said signal line to simultaneously transmit said intermediate frequency to said control module and a DC power signal from said control module.
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15. The apparatus of claim 14, wherein said signal line comprises a twisted pair of conductors.
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16. A capacitive sensing element, comprising:
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a single non-contact capacitive strip having a nominal capacitance value; and
a capacitance detection circuit integrated within said capacitive strip, said capacitance detection circuit further comprising;
a first oscillator coupled to the capacitive strip, said first oscillator generating a first frequency dependent upon the capacitance value of the capacitive strip; and
a second oscillator generating a reference frequency, said reference frequency being offset from said first frequency by a fixed offset value when the capacitance of said capacitive strip equals said nominal capacitance value;
wherein a change in capacitance of the capacitive strip from said nominal capacitance value is detected if said first frequency differs from said reference frequency by mere than said fixed offset value.
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Specification