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

Medkcal research has an urgent nieed for a small, accurate, stable, low-power, biocomnpatible, and inexpensive pressure sensor with a zero to full-scale range of 0-300 mmHg. A comparison of fundamenital 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 capacitanice, hatve previously prevented the realilzation of this accuracy. An integrated circuit (IC) for use with acapacitive pressure transducer was designed, built, and tested. Capacitance is measured by a new ratiomnetric scheme employing an on-chip reference capacitor. The typical random pressure measuarement error due to resolution and nonlinearitiy is ±0.4 mmHlg (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 ature compensation of the transducer.