| 摘要 |
PURPOSE:To make the titled device small-sized and light weight with a simple constitution and to attain sure rotating speed control, by making the rotation of a disc as constant line speed, with a reproduced modulation signal and a clock signal picked up from the modulation signal. CONSTITUTION:A counter 13 counts a clock signal at a terminal 15 only when a modulation signal is at H level. The said count output a summed with a count value of a latch circuit 16 and latched to the circuit 16 again. A counter 14 outputs a control signal to the latch circuit 16 when the N-th H level of the said signal goes to L level, and the circuit 16 outputs the total summing value to an average value circuit 17. The circuit 17 calculates the average value of a clock signal number. A difference output between this average value and a theoretical average value A at a terminal 18 is converted into a voltage at a D-A converting circuit 19 and the rotating speed is controlled. That is, the rotating speed can be controlled so that the difference with the theoretical average value is zero. |
