Frequency output piezoresistive pressure sensor

• Published in: Sensors and actuators Vol. 4; pp. 77 - 83
• Main Authors: French, P.J., Dorey, A.P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1983
• ISSN: 0250-6874
• DOI: 10.1016/0250-6874(83)85011-2

The sensitivity of silicon to strain and its application to the fabrication of integrated circuits enable sensors to be designed which provide the primary sensing and digital encoding of the signal within the same piece of material. One possible configuration, originally described by Reichl, uses a resistor as the basic sensor to vary the injector currents in an I 2L ring oscillator. The change in value of the resistance causes a change in the delay of the I 2L gates and hence changes the frequency of the oscillator. If two such oscillators are used with the resistors associated with them being subjected to opposite strains, a differential frequency is provided which incorporates a first-order cancellation of temperature effects. This frequency difference may be detected digitally and encoded for transmission within a microprocessor-based measurement system. An NMOS circuit to carry out this function has been designed.