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Self-testing capacitive pressure transducer and method

  • US 5,377,524 A
  • Filed: 06/22/1992
  • Issued: 01/03/1995
  • Est. Priority Date: 06/22/1992
  • Status: Expired due to Term
First Claim
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1. A self-testable micromachined transducer apparatus for measuring at least one externally applied condition, the transducer apparatus including at least one solid-state capacitive pressure sensor, the transducer apparatus comprising:

  • a rigid support substrate;

    a solid-state micromachined pressure sensor, formed at least in part on the support substrate and having a flexible member and a capacitor adjustable by varying pressure applied to the flexible member; and

    an electronic read-out circuit, electrically coupled to the solid-state pressure sensor, the read-out circuit including;

    (1) a solid-state operational amplifier for producing an analog output signal corresponding to a charge applied to the adjustable capacitor, the amplifier having first and second differential input terminals, and an output terminal upon which the analog output signal is placed, with the first input terminal connected to the adjustable capacitor,(2) a reference capacitor connected to the first input terminal of the operational amplifier,(3) an integrating capacitor connected to the first input terminal and the output terminal of the operational amplifier,(4) means for providing a reset signal to the read-out circuit, the reset signal having a precharge portion and an integration portion which establishes an integration period during which the analog output signal is produced;

    (5) means for applying at least one clock signal which alternates between two states substantially in synchronization with transitions between the precharge portion and the integration portion of the reset signal, to the adjustable capacitor and to the reference capacitor, with the beginning of the integrating portion coinciding with the beginning of the integration period established by the reset signal, whereby an output signal is generated on the output terminal of the operational amplifier during the integrating portion of the reset signal; and

    (6) means for selectively extending at least one precharge portion of the reset signal so as to cause the flexible member to deflect to a maximum steady-state deflection immediately prior to an integration portion of the reset signal, wherein the means for selectively extending causes the transducer apparatus to be self-tested by determining whether the value of the analog output signal from the operational amplifier includes an electrostatic deflection component consistent with predetermined expectations about same.

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