Self-testing capacitive pressure transducer and method

A self-testable electronic system located in immediate proximity to a miniature transducer including a solid-state capacitive pressure sensor having an adjustable capacitor with generally parallel electrically conductive plates, the capacitor being responsive to an external force, the electronic system providing electronic read-out signals corresponding to the forces sensed by the adjustable capacitor, the electronic system comprising:

• a read-out circuit for reading a parameter of the adjustable capacitor correlatable to the magnitude of an external force applied to the capacitor, the read-out circuit including,
• (1) a solid-state amplifier for producing an output signal corresponding to a charge applied to the adjustable capacitor, the amplifier having at least a first input terminal and an output terminal upon which the output signal is placed, with the first terminal being adapted for connection to the adjustable capacitor,
• (2) an integrating capacitor connected to the first input terminal and the output terminal of the operational amplifier,
• (3) means for providing a reset signal to the read-out circuit to establish the beginning of an integration cycle, said reset signal including a precharge portion and an integration portion,
• (4) means for applying synchronized clock input signals in synchronization with the reset signal, and
• (5) means for testing the system by applying a predetermined electrostatically generated force to the adjustable capacitor, said means for testing the system extending at least one precharge portion of the reset signal so as to cause a maximum steady-state electrostatic condition on the adjustable capacitor, wherein the means for testing the system determines whether the value of the output signal from the solid-state amplifier after the steady-state electrostatic condition is placed on the capacitor is consistent with predetermined expectations.

A method of operating a solid state transducer which employs a capacitive pressure sensor and a switched capacitor electronic read-out circuit, the capacitive pressure sensor including at least one adjustable capacitor responsive to at least one variable external condition, the method comprising the steps of:

• (a) obtaining successive read-outs with each such read-out corresponding to a value of the external conditions then sensed by the capacitor, by applying repetitively a waveform having a frequency above a first pre-determined frequency to the adjustable capacitor of the capacitive pressure transducer;
• (b) generating by use of an electric signal an electrostatic force upon the capacitor of the pressure sensor by selectively holding the waveform in a pre-determined state for a length of time exceeding the normal period of the cycle of the waveform by at least an order of magnitude so as to cause a maximum steady-state condition on the capacitor;
• and
• (c) after releasing the waveform from the pre-determined state, immediately obtaining a read-out from the waveform to obtain an output signal including a component due to the electrostatic force generated during the last step.