Analysis, Design, and Performance of a Capacitive Pressure Sensor IC

Abstract

Medical research has an urgent need for a small, accurate, stable, low-power, biocompatible, and inexpensive pressure sensor with a zero to full-scale range of 0–300 mmHg. A comparison of fundamental transducer limits shows that the capacitive device offers better accuracy than the piezoresistive type. Limitations of the on-board circuitry, needed to buffer the transducer capacitor against parasitic capacitance, have previously prevented the realization of this accuracy. An integrated circuit (IC) for use with a capacitive pressure transducer was designed, built, and tested. Capacitance is measured by a new ratiometric scheme employing an on-chip reference capacitor. The typical random pressure measurement error due to resolution and nonlinearity is ±0.4 mmHg (with a full-scale of 300 mmHg). The long-term systematic error due to falling battery voltage is ±0.6 mmHg. These figures were calculated from measurements of temperature, supply dependence, and nonlinearity on completed integrated circuits. The sensor IC allows measurement of temperature to ±0.1°C for temperature compensation of the transducer. Copyright © 1986 by The Institute of Electrical and Electronics Engineers, Inc.