Abstract: A micromachined accelerometer includes two capacitors comprising a pair of fixed capacitor electrodes and an intermediate movable proof mass serving as a common electrode which is displaced under acceleration to differentially vary the capacitances. A circuit holds the common electrode at a bias voltage and a switching circuit rapidly alternating between two phases separately connects the fixed electrodes to a main reference voltage and to ground during a first phase and to a common intermediate voltage during a second phase. A charge amplifier senses capacitance changes due to acceleration to produce an output voltage and an attenuating amplifier responsive to the output voltage produces the common intermediate voltage. A compensation servo circuit responsive to the output voltage generates the bias voltage which controls an electrostatic balancing force which is applied to the proof mass during the first phase to maintain the proof mass near a rest position.

Abstract: A quad-gate demodulator circuit for capacitive transducers in which analog gate devices replace the diodes of a prior art diode-quad bridge circuit. This improvement eliminates the temperature and ratiometricity errors associated with the diode-quad circuit.

Abstract: A capacitive pressure transducer system includes a reference capacitor and a capacitor which varies with pressure; and circuitry which involves alternately charging one of the capacitors to a reference voltage level, and then switching to charge the other capacitor; and circuitry for producing an output voltage which varies as the duty cycles of the two capacitors shift; and the output is therefore substantially proportional to the pressure changes. Feedback is provided to incrementally change the capacitor charging and switching timing or duty cycles by changing the charging current or the reference voltage at which switching occurs, to substantially eliminate deviations from linearity in the voltage versus pressure characteristic.

Abstract: A compensation technique and network circuitry for a quad-diode demodulator and capacitive transducer combination is disclosed. The compensation method includes varying the amplitude of an alternating carrier frequency oppositely to the changes produced in that amplitude by the compensable errors in the demodulator and transducer. In one preferred embodiment ratiometric compensation and temperature compensation for the demodulator and any capacitive transducer is produced. In a second embodiment linearization and temperature compensation for the demodulator and a quartz capacitive transducer is provided.