Capacitive temperature compensation for a pressure sensor
First Claim
1. A capacitor temperature compensation circuit for use at a predetermined operative frequency of an operative electrical signal to be applied to and/or determined by a capacitor, comprising:
- a first capacitor connected between two end terminals, said first capacitor having a predetermined temperature coefficient of capacitance (TCC) with a predetermined polarity and providing a predetermined capacitive impedance at a predetermined operative signal frequency of a signal to be applied to and/or determined by said first capacitor;
an additional compensation capacitor connected in series with a resistor, said additional capacitor having a predetermined temperature coefficient of capacitance with a predetermined polarity opposite to said first capacitor temperature coefficient of capacitance polarity, said series connection of said additional capacitor and said resistor being connected in parallel with said first capacitor across said two end terminals; and
means for providing, at at least one of said two end terminals, a signal having a predetermined operative signal frequency, said resistor providing a nonnegligible resistive impedance at said predetermined operative signal frequency as compared to said first capacitor impedance and said additional capacitor impedance at said predetermined operative signal frequency, whereby the composite temperature coefficient of capacitance of said first and additional capacitors across said two end terminals is effectively determined by the magnitude of said resistor impedance.
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Accused Products
Abstract
The undesired temperature variation of a capacitive pressure sensing element (10) having a positive temperature coefficient of capacitance (TCC) is compensated by a series resistor R and compensating capacitor (Cc) connected in parallel to the pressure sensing capacitor (Cx). The compensating capacitor and presssure sensing element have opposite polarity temperature coefficients of capacitance, and the magnitude of the resistor is selected such that its resistive impedance is nonnegligible and is comparable to the magnitude of the capacitive reactance of the pressure sensing capacitor or compensating capacitor at a predetermined operative frequency of an electrical signal applied to and/or determined by the pressure sensing and compensating capacitors.
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Citations
20 Claims
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1. A capacitor temperature compensation circuit for use at a predetermined operative frequency of an operative electrical signal to be applied to and/or determined by a capacitor, comprising:
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a first capacitor connected between two end terminals, said first capacitor having a predetermined temperature coefficient of capacitance (TCC) with a predetermined polarity and providing a predetermined capacitive impedance at a predetermined operative signal frequency of a signal to be applied to and/or determined by said first capacitor; an additional compensation capacitor connected in series with a resistor, said additional capacitor having a predetermined temperature coefficient of capacitance with a predetermined polarity opposite to said first capacitor temperature coefficient of capacitance polarity, said series connection of said additional capacitor and said resistor being connected in parallel with said first capacitor across said two end terminals; and means for providing, at at least one of said two end terminals, a signal having a predetermined operative signal frequency, said resistor providing a nonnegligible resistive impedance at said predetermined operative signal frequency as compared to said first capacitor impedance and said additional capacitor impedance at said predetermined operative signal frequency, whereby the composite temperature coefficient of capacitance of said first and additional capacitors across said two end terminals is effectively determined by the magnitude of said resistor impedance. - View Dependent Claims (2, 3, 4, 5)
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6. A method for adjusting temperature variation of a capacitor, comprising the steps of:
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providing a first capacitor between two end terminals, said first capacitor having a predetermined coefficient of capacitance (TCC) with a predetermined polarity; connecting in parallel with said first capacitor across said two end terminals a series circuit comprising of a resistor connected in series with an additional capacitor, said additional capacitor having a predetermined TCC with a predetermined polarity opposite to the TCC polarity of said first capacitor; providing an electrical signal having a predetermined operative signal frequency to the said series circuit and said first capacitor; and changing the resistance in said series circuitry to achieve a desired composite TCC across said two terminals for the combination of said series circuit and said first capacitor, said resistance, when said desired composite TCC is achieved, providing a nonnegligible impedance at said operative signal frequency as compared to the impedances of said first or additional capacitors at said operative signal frequency. - View Dependent Claims (7, 8, 9, 10)
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11. A capacitive sensor with temperature compensation comprising:
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a capacitive transducer element connected between two end terminals, said capacitor transducer element providing between said end terminals a variable capacitance which varies in accordance with a variable parameter, other than temperature, the magnitude of which is desired to be sensed, said variable capacitance having a predetermined temperature coefficient of capacitance (TCC) with a predetermined polarity which provides an undesired capacitance variation as a function of temperature; sensor circuit means, including said capacitive transducer element, in which an electrical signal at a predetermined operative frequency is applied to said transducer element to provide an output signal varying in accordance with the capacitance variation of said transducer element provided across said two end terminals in response to said sensed variable parameter; and compensation means, coupled to said transducer element, for altering the temperature variation of said output signal, said compensation means comprising, a series circuit comprising a compensation capacitor connected in series with a resistor, said series circuit being connected across said end terminals and in parallel to said capacitive transducer element, said compensation capacitor having a temperature coefficient of capacitance of opposite polarity with respect to the polarity of the temperature coefficient of capacitance of said variable capacitance, and said resistor providing a nonnegligible resistive impedance at said predetermined operative frequency with respect to the reactive impedances of said variable capacitance or said compensation capacitor, whereby said series circuit can provide for adjusting the temperature variation of said output signal by adjusting the magnitude of said resistor. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification