ALC crystal oscillator based pressure and temperature integrated measurement system for high temperature oil well applications

An application specific integrated circuit for the pressure and temperature measurement at the high temperature oil well bottom conditions, is presented in this paper. The system is mainly composed of three high performance Automatic Level Controlled (ALC) oscillator circuits which drive three external crystals (the sensitive elements), and of some mixing and filtering stages. The integrated system was successfully tested up to 220/spl deg/C, showing a frequency resolution of 0.0003 ppm (0.0007 psi, for the pressure measurement) and a drift of 1.5 Hz/month (/spl sim/0.5 psi/month), concerning respectively the short and long term measurement stability. A drastic reduction of the whole measurement tool size and cost will be allowed by means of this application specific BiCMOS integrated circuit.