Frequency encoding closed loop circuit with transducer
First Claim
1. A method for producing an output frequency which is a function of the amplitude of a varying physical quantity acting on a transducer having an output impedance, the method comprising the steps of:
- generating, in a relaxation oscillator with an input impedance, a digital drive signal at the output frequency;
driving the transducer with a function of the digital drive signal and producing an amplitude modulated bilevel signal in-phase with the drive signal and having an amplitude which is a function of the amplitude of the physical quantity sensed by the transducer;
isolating the output impedance of the driven transducer from the input impedance of the relaxation oscillator;
combining the drive signal and the amplitude modulated bilevel signal, thereby providing a composite signal; and
feeding the composite signal back as the input to the relaxation oscillator.
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Accused Products
Abstract
A frequency encoding closed loop circuit with transducer, comprising a closed inner digital loop nested in a closed outer loop which carries both digital and analog signals, associates a corresponding frequency output to variations in the magnitude of physical quantity input to a transducer which is contained within the outer loop. The encoder achieves the advantage of synchronous detection in converting changes in a transduced quantity into a frequency count. The encoder produces frequency shifts at its output that are proportional to the transducer input and are significantly immune to noise and power input fluctuations.
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Citations
20 Claims
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1. A method for producing an output frequency which is a function of the amplitude of a varying physical quantity acting on a transducer having an output impedance, the method comprising the steps of:
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generating, in a relaxation oscillator with an input impedance, a digital drive signal at the output frequency; driving the transducer with a function of the digital drive signal and producing an amplitude modulated bilevel signal in-phase with the drive signal and having an amplitude which is a function of the amplitude of the physical quantity sensed by the transducer; isolating the output impedance of the driven transducer from the input impedance of the relaxation oscillator; combining the drive signal and the amplitude modulated bilevel signal, thereby providing a composite signal; and feeding the composite signal back as the input to the relaxation oscillator. - View Dependent Claims (2, 3, 4, 5)
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6. A frequency encoding closed loop circuit with transducer comprising:
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an inner loop comprising a relaxation oscillator having a bilevel input of variable amplitude and having as an output a fixed amplitude digital drive signal, the frequency of the drive signal being a function of the amplitude of the bilevel input to the relaxation oscillator; and an outer loop comprising;
(a) a transducer excitable by a physical quantity input of variable magnitude;
(b) means for driving the transducer with the digital drive signal to provide an amplitude modulated output signal which selectively varies between two signal levels, the two signal levels being a function of the magnitude of the physical input;
(c) the inner loop;
(d) means for additively combining the amplitude modulated signal with the drive signal to provide a composite signal;
(e) means for entering the composite signal at the input to the relaxation oscillator of the inner loop for controlling the frequency of the drive signal. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A sensor system comprising a plurality of frequency encoding closed loop circuits with transducers wherein each circuit comprises:
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an inner loop comprising a relaxation oscillator having a digital input of variable amplitude and having as its output a fixed amplitude digital drive signal, the frequency of the drive signal being a function of the amplitude of the digital input to the relaxation oscillator; an outer loop comprising;
(a) a transducer excitable by a variable physical input, said transducer having an electrical output;
(b) means for driving the transducer with the digital drive signal to provide an amplitude modulated signal from the transducer, which selectively varies between two signal levels, the two signal levels being a function of the magnitude of the physical quantity input (c) the inner loop;
(d) means for additively combining the amplitude modulated signal with the drive signal to provide a composite signal; and
(e) means for entering the composite signal as the input to the relaxation oscillator of the inner loop; anda pair of wires connected for providing power to all the circuits and for providing at a selected time, a signal indicative of the amplitude modulated signal from a selected one of the circuits. - View Dependent Claims (20)
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Specification