Optimization of a BiCMOS integrated transducer for self-compensated capacitive pressure sensor

Two new pressure sensor demonstrators have been designed and mounted using silicon/Pyrex capacitive sensing cells and analog-digital BiCMOS transducers. A ratiometric scheme has been used to self-compensate thermal drifts and nonlinearities. The first demonstrator implemented with four chips is characterized by a relative sensitivity close to -1.85%/bar, a nonlinearity of the order of 1.1%FS and an offset thermal coefficient smaller than 20 ppm//spl deg/C. The second one has been implemented with two integrated chips. It consists, on the one hand, of two pairs of converters and counters integrated in the same chip, and on the other hand, of a reference and measurement capacitors into the same sensing cell. This configuration permits one to reduce stray capacitors by a factor of two but also provokes interference between oscillators. Characterization and PSPICE modeling have permitted understanding of localized causes and then proposes some solutions to avoid and/or minimize these problems.