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US 4,289,035 AGranted
Compensated capacitive transducer demodulator circuit
AssigneeThe Bendix Corporation
InventorChen Y. Lee
Life of this patent
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Abstract
A compensation technique and network circuitry for a quad-diode demodulator and capacitive transducer combination is disclosed. The compensation method includes varying the amplitude of an alternating carrier frequency oppositely to the changes produced in that amplitude by the compensable errors in the demodulator and transducer. In one preferred embodiment ratiometric compensation and temperature compensation for the demodulator and any capacitive transducer is produced. In a second embodiment linearization and temperature compensation for the demodulator and a quartz capacitive transducer is provided.
Claims21
A capacitive transducer and demodulator combination circuit comprising:
- a capacitive transducer for measuring the variances of a physical parameter, said transducer adapted to transform the variances into changes of capacitance of the transducer;
- a frequency generator means for supplying an alternating carrier voltage;
- a quad-diode demodulator electrically connected to receive from said frequency generator means the alternating carrier voltage and further connected to said transducer such that the changes in capacitance modulate said carrier, said demodulator detecting said carrier and generating an output voltage signal representative of the variances in the measured physical parameter;
- and
- compensation network means, electrically connected to said frequency generator, for varying the amplitude of the carrier voltage oppositely to the amplitude changes in the output signal produced by the compensable errors of the demodulator and transducer.
2 more elements
A capacitive transducer and demodulator combination circuit comprising:
- a capacitive transducer for measuring the variances of a physical parameter and for transforming the variances into changes in capacitance of the transducer, wherein said transducer has a variable capacitor C.sub.p which changes capacitance with respect to the physical variable and a reference capacitor C.sub.r which is substantially unchanging with respect to the physical parameter;
- a quad-diode demodulator electrically connected to the capacitive transducer and electrically connected to a frequency generator means for supplying an alternating carrier voltage such that the carrier voltage is modulated and detected to generate an output voltage signal representative of the variances in the measured physical parameter, said demodulator having a voltage transfer function of:
- V.sub.dc =2(V.sub.p -V.sub.d)(C.sub.p -C.sub.r)/(C.sub.p +C.sub.r)
- where V.sub.dc is said output voltage signal, V.sub.p is the voltage amplitude of said alternating carrier voltage, and V.sub.d is the voltage drop across one of the diodes of said demodulator;
- and
- compensation network means, electrically connected to said frequency generator, for varying the amplitude of the carrier voltage oppositely to the amplitude changes in the output signal produced by the compensable errors of the demodulator and transducer.
3 more elements
A transducer and demodulator combination circuit comprising:
- a transducer for measuring the variances of a physical parameter, said transducer adapted to transform the variances into changes of impendance of the transducer;
- a frequency generator means for supplying an alternating carrier voltage which is a ratiometric function of an input supply voltage;
- a demodulator electrically connected to receive from said frequency generator means the alternating carrier voltage and further connected to said transducer such that the changes in impedance modulate said carrier, said demodulator detecting said carrier and generating an output voltage signal representative of the variances in the measured physical parameter;
- and
- compensation network means for varying the amplitude of the carrier voltage oppositely to the amplitude changes in the output signal produced by the compensable errors of the demodulator and transducer wherein said compensation network means includes means for providing ratiometric compensation for the ratiometric error of said demodulator.
2 more elements
A transducer and demodulator combination circuit comprising:
- a transducer for measuring the variances of a physical parameter, said transducer adapted to transform the variances into changes of impedance of the transducer;
- a frequency generator means for supplying an alternating carrier voltage;
- a quad-diode demodulator having a voltage transfer function relatively independent of carrier waveform and frequency electrically connected to receive from said frequency generator means the alternating carrier voltage and further connected to said transducer such that the changes in impedance modulate said carrier, said demodulator detecting said carrier and generating an output voltage signal representative of the variances in the measured physical parameter;
- and
- compensation network means, electrically connected to said frequency generator, for varying the amplitude of the carrier voltage oppositely to the amplitude changes in the output signal produced by the compensable errors of the demodulator and transducer.
2 more elements
Dependencies are inferred from the claim text.