| 摘要 |
PURPOSE:To bring the disc rotation quickly from the standstill to the vicinity of the specified line speed and to attain ease of reproducing clock extraction afterward, by applying at first rotation acceleration at disc start to drive the disc near the specified speed and then switching the control to the frame synchronism servo. CONSTITUTION:The recording disc is accelerated once by applying a prescribed voltage (or current) to a motor for a prescribed time in response to a rotation start command. A reproduced RF signal from a pickup 2 is shaped at a waveform shaping device 3 to obtain an EMF signal. This signal is inputted to a frame synchronism servo device 4 and a frame synchronism servo signal is generated. This servo signal is impressed to a spindle drive device 6 via a switching device 5 to apply the SYNC servo to the spindle motor. Since a constant voltage +V is impressed to the spindle drive device 6 via a low resistance Ro1, a large constant current (or constant voltage) is applied to the spindle motor in case of the ACC operation of the accelerating function. In case of HDL operation, a small constant current (or constant voltage) is applied to the spindle motor so that the value of resistor R02 is selected larger then the value of resister R01 and the HLD operation is attained. |
