| 摘要 |
PURPOSE:To automatically adjust the phase shift of an active filter, etc., as an object of automatic adjustment by providing a phase control loop which includes a variable phase shifting circuit and using a phase shifting circuit of the same circuit constitution with the variable phase shifting circuit for the active filter as the object of automatic adjustment. CONSTITUTION:The variable phase shifting circuit 3, a phase comparing circuit 4, a low-pass filter 5, and a voltage-controlled constant current circuit 6 forms the phase control loop for adjusting the phase shift quantity of the variable phase shifting circuit 3 so that the phase shift quantity is invariably 90 deg.. The frequency characteristics of the active filter are set by the adjustment of the variable phase shifting circuit 3 included in the phase control loop, and this phase shifting circuit is a phase shifting circuit having circuit constitution similar to that of the variable phase shifting circuit 3 included in the phase control loop. The phase shift quantity of the phase shifting circuit in the active filter 7 is adjusted with a constant current output outputted by the voltage-controlled constant current circuit 6 through the operation of the phase shift control loop and the frequency characteristics of the active filter 7 are automatically adjusted.
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