Method of detecting a variation in stray capacitance by use of a PLL circuit
First Claim
1. A method of detecting a variation in stray capacitance by use of a PLL circuit, comprising the steps of:
- setting respectively a freerunning frequency and a capture range of a phase-locked loop circuit so that a range in which an output frequency of a pre-oscillator changes extends to an interior of said capture range of said phase-locked loop circuit, said output frequency being determined by a synthetic time constant obtained by adding up a variation value of an electric capacitance that is detected by a sensor and a reserve time constant preset in a time constant determining module when detecting the stray capacitance by employing said sensor for detecting the variation in the stray capacitance in contact or non-contact with a body to be detected and a capacitance detecting means including said pre-oscillator having said time constant determining module connected to said sensor and said phase-locked loop circuit connected to said pre-oscillator;
detecting a change in a freerunning frequency control voltage in a locked state of said phase-locked loop circuit, the change being caused with the variation in the electric capacitance that is detected by said sensor; and
detecting a state variation of said detected body.
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Accused Products
Abstract
Disclosed is a method of detecting a variation in stray capacitance by use of a PLL circuit. This method involves the steps of: setting respectively a freerunning frequency and a capture range of a phase-locked loop circuit so that a range in which an output frequency of a pre-oscillator changes extends to an interior of the capture range of the phase-locked loop circuit, the output frequency being determined by a synthetic time constant obtained by adding up a variation value of an electric capacitance or the like that is detected by a sensor and a reserve time constant preset in a time constant determining module when detecting the stray capacitance by employing the sensor for detecting the variation in the stray capacitance in contact or non-contact with a body to be detected and a capacitance detecting means including the pre-oscillator having the time constant determining module connected to the sensor and the phase-locked loop circuit connected to the pre-oscillator; detecting a change in a freerunning frequency control voltage in a locked state of the phase-locked loop circuit, the change being caused with the variation in the electric capacitance or the like that is detected by the sensor; and detecting a state variation of the detected body.
18 Citations
6 Claims
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1. A method of detecting a variation in stray capacitance by use of a PLL circuit, comprising the steps of:
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setting respectively a freerunning frequency and a capture range of a phase-locked loop circuit so that a range in which an output frequency of a pre-oscillator changes extends to an interior of said capture range of said phase-locked loop circuit, said output frequency being determined by a synthetic time constant obtained by adding up a variation value of an electric capacitance that is detected by a sensor and a reserve time constant preset in a time constant determining module when detecting the stray capacitance by employing said sensor for detecting the variation in the stray capacitance in contact or non-contact with a body to be detected and a capacitance detecting means including said pre-oscillator having said time constant determining module connected to said sensor and said phase-locked loop circuit connected to said pre-oscillator; detecting a change in a freerunning frequency control voltage in a locked state of said phase-locked loop circuit, the change being caused with the variation in the electric capacitance that is detected by said sensor; and detecting a state variation of said detected body. - View Dependent Claims (2, 3, 4, 5)
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6. A method of detecting a variation in stray capacitance by use of a PLL circuit, comprising the steps of:
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providing a sensor for detecting a variation in the stray capacitance in contact or non-contact with a body to be detected, a phase-locked loop circuit including a time constant determining module connected to said sensor and a pre-oscillator connected to said phase-locked loop circuit and having an intrinsic output frequency; setting respectively a freerunning frequency and a capture range of said phase-locked loop circuit so that the capture range is brought into a first state to include the intrinsic output frequency of said pre-oscillator with a variation in electric capacitance that is detected by said sensor or into a second state to release from the included intrinsic output frequency of said pre-oscillator, the capture range being defined based on a freerunning frequency of a voltage control oscillator that is determined by a synthetic time constant obtained by adding up a variation value of the electric capacitance which is detected by said sensor and a reserve time constant preset in said time constant determining module; detecting the variation in the freerunning control voltage in the locked state of said phase-locked loop circuit, the variation being caused with the change in the electric capacitance that is detected by said sensor; and detecting a state variation of said detected body.
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Specification