| 摘要 |
A circuit for relatively accurately measuring the capacitance of a pair of capacitive elements which may be part of an accelerometer. The circuit includes a drive circuit, a switching circuit, a pair of bridge capacitors and a detector circuit. The bridge capacitors and the capacitive elements are connected together to form a bridge. Common nodes between the capacitive elements and the bridge capacitors are interconnected together by the switching circuit in a first mode of operation to force a reference or null condition to enable the common nodes to discharge to a predetermined reference voltage. The common nodes are isolated from one another in a second mode of operation during which time the bridge is charged to a predetermined voltage by the drive circuit to enable the detector circuit connected to the common nodes to detect differences in voltage between each of the two common nodes. In order to reduce errors resulting from unequal leakage currents and junction capacitances, the switching circuit is configured as a single JFET which additionally reduces the parts count and ultimately the cost of the accelerometer. In addition, capacitive elements are referenced to the pick-off drive voltage which maintains a relatively high detector gain under conditions where one of the capacitive elements is shorted, thereby enabling a relatively quick recovery from such a condition. |
