| 摘要 |
PURPOSE:To attain the stable lead-in of a servo loop by supplying an error signal to its amplifying means via a signal attenuating means which reduces gradually the signal attenuation amount in response to a control signal and also using an offset erasing means. CONSTITUTION:A transistor TR Q1 is turned on when a loop control signal (b) is set at a low level. Then the charging voltage of a capacitor C rises up gradually by the constant current output of a current mirror circuit 10. Thus the gate voltage of an FET 9 also rises up gradually and the source-drain impedance of the FET 9 is gradually reduced down to the resistance level of an ON mode from infinity . As a result, the gain of a signal attenuator 8 is changed gradually to 1 from 0 and the signal attenuation amount is reduced gradually. Therefore the output of an equalizer amplifier 7 can change within the maximum output range if the output voltage of an offset control circuit 11 is set previously so that the output offset of the amplifier 7 is eliminated. Thus no stepped change is produced to secure the stable lead-in of a servo loop.
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