| 摘要 |
PURPOSE:To shorten and stabilize especially the pull-in time in a tracking servo circuit by raising gains at the high frequency side further than usual and dropping gains at the low frequency side immediately after a servo lock is turned on and raising gains at the low frequency side as the time expires so as to improve the accuracy of the servo. CONSTITUTION:The positive side of an operational amplifier 2 is grounded, and between its negative side and an input terminal 3 a parallel circuit composed of a resistance 4 and a capacitor 5 is inserted. On a feedback path between the negative side and an output terminal 6 an active filter 10 available from connecting a fixed resistance 7, a capacitor 8 and an FET 9 as a variable resistance each other in parallel is inserted. The gate of the FET 9 is grounded and simultaneously is jointed to a minus electric power source terminal 14. When a positive voltage is given across the gate and source of the FET 9 and they are turned on with such circuit constitution, the resistance value as a variable resistance is small, whereas the folding point frequency F3 of the active filter 10 is large. Since a loop gain characteristic at this time is high in a high frequency band, the pull-in is smoothly executed, and the control accuracy of the servo is slowly improved as the time expires.
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