Capacitive-type physical quantity sensor
First Claim
1. A capacitive-type physical quantity sensor comprising:
- first and second substrates provided separately;
a sensor element formed on the first substrate and having moving electrodes and first and second fixed electrodes, the moving electrodes undergoing a displacement depending upon a change in physical quantity, and the first and second fixed electrodes being arranged to face the moving electrodes and receive periodic carrier waves having phases opposite to each other; and
a detector circuit formed on the second substrate and including a C-V conversion circuit that receives a signal that varies depending upon a change in a capacitance formed between the moving electrodes and the first and second fixed electrodes, the detector circuit producing a voltage that varies depending upon a change in the capacitance, whereinthe C-V conversion circuit includes an operational amplifier and a reference voltage supply circuit, the operational amplifier having a first input terminal to receive a signal that varies depending upon a change in the capacitance and a second input terminal to receive a reference voltage of the reference voltage supply circuit, and whereinthe first substrate is electrically connected to the second input terminal of the operational amplifier so that the voltage of the first substrate is fixed to the reference voltage of the reference voltage supply circuit.
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Accused Products
Abstract
A substrate forming a sensor element is connected to a non-inverting input terminal of an operational amplifier, and a common voltage is applied thereto from a reference voltage supply circuit to fix them to the same potential. Thus, the impedances of the non-inverting input terminal and of the inverting input terminal of the operational amplifier are matched with respect to the power source. Therefore, noise superposed on a power source line can be greatly decreased by noise-removing characteristics determined by CMRR characteristics of the operational amplifier. As a result, a capacitive-type acceleration sensor exhibits sensor characteristics of frequency noise suppressing effect.
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Citations
10 Claims
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1. A capacitive-type physical quantity sensor comprising:
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first and second substrates provided separately; a sensor element formed on the first substrate and having moving electrodes and first and second fixed electrodes, the moving electrodes undergoing a displacement depending upon a change in physical quantity, and the first and second fixed electrodes being arranged to face the moving electrodes and receive periodic carrier waves having phases opposite to each other; and a detector circuit formed on the second substrate and including a C-V conversion circuit that receives a signal that varies depending upon a change in a capacitance formed between the moving electrodes and the first and second fixed electrodes, the detector circuit producing a voltage that varies depending upon a change in the capacitance, wherein the C-V conversion circuit includes an operational amplifier and a reference voltage supply circuit, the operational amplifier having a first input terminal to receive a signal that varies depending upon a change in the capacitance and a second input terminal to receive a reference voltage of the reference voltage supply circuit, and wherein the first substrate is electrically connected to the second input terminal of the operational amplifier so that the voltage of the first substrate is fixed to the reference voltage of the reference voltage supply circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification