| 摘要 |
A capacitance-type electrostatic servo acceleration sensor capable of detecting applied acceleration with high sensitivity and with low error without needing an accurate oscillator. The sensor makes use of a PAM (pulse amplitude-modulation) circuit for performing pulse amplitude-modulation in proportion to the acceleration. The sensor is equipped with a capacitance-detecting portion having a movable electrode and a pair of fixed electrodes located on opposite sides of the movable electrode. The movable electrode is displaced in response to the acceleration. A comparator is formed by an operational amplifier, and a servomechanism is formed. The electrically obtained open gain of this operational amplifier is set sufficiently greater than the mechanically obtained gain of the capacitance-detecting portion. A measurement mode period and a force-balanced mode period are repeated alternately. During the measurement mode period, the movable electrode is not constrained by the servomechanism, and a voltage corresponding to the acceleration is applied to a sample-and-hold amplifier. During the force-balanced mode period, the movable electrode is constrained by the servomechanism according to the output from the sample-and-hold amplifier which corresponds to the acceleration, and the movable electrode is short-circuited to ground.
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