| 摘要 |
PURPOSE:To detect a synchronous signal by triggering a timer circuit in every input of one inversion of a digital signal, and when the succeeding one inversion does not reach during the period of about 2 times the max. inversion time, outputting a signal from the time circuit. CONSTITUTION:If the relative speed of a disc 1 is slower than regularly prescribed speed vO, an output signal from a triggerable monostable multivibrator (MMV) 6 or 7 is inverted from ''L'' to ''H'' during the period 22T when at least a frame synchronous signal exists. An MMV9 is triggered by said inversion through an OR gate 8. When the MMV9 is triggered, the MMV9 outputs an H signal during a prescribed period T1 and the output signal is integrated by an LPF10 and compared with reference voltage. If the reference volage is set up to a half of the voltage VO corresponding to voltage generated by an F/V converting circuit 11 when the disc 1 travels at the regular speed vO, a comparator 13 outputs a positive output signal, increasing the number of rotations of a motor 2. |
