PURPOSE: To obtain a capacity detection circuit in which the ratio of capacity can be detected stably regardless of the ambient temperature by eliminating the effect of offset voltage of amplifier or the charges of a switching transistor.
CONSTITUTION: The capacity detection circuit comprises a switched capacitor circuit 15, sample hold circuits 16, 17, a differential amplifier circuit 18, a sensor drive circuit and a logic circuit. The sensor capacitor constituting the feedback capacity of the switched capacitor circuit 15 is discharged immediately before the level of a signal for driving a reference capacitor is changed. Output voltage from the switched capacitor circuit 15 is sampled and held in synchronism with the drive timing of reference capacitor and the difference signal between both signals is taken out. This circuitry eliminates the common mode disturbance, e.g. temperature drift, being mixed in the capacity detection circuit thus realizing a capacity detection circuit excellent in offset and the temperature drift thereof.
OKADA HIROYUKI
KURIYAMA TOSHIHIDE
TSURUGA KIKUO
TOKIN CORP
| JPS59168168U | 1984-11-10 |
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