| 摘要 |
PURPOSE:To make the line speed constant easy and with high accuracy, by counting the period between (1) and (0) of a reproducing signal with a clock pulse, generating an acceleration signal when the count value is prescribed value or over, and decelerating when the specified count value is not obtained. CONSTITUTION:The 1st and 2nd differentiation circuits 2 and 8 output differetiation pulses P1 and P2 of a reproducing signal A. Counters 12 and 13 count a clock pulse CP while being cleared with the pulses P1 and P2. The output value of shift registers 14 and 15 represents the number of the pulse CP at the period between (1) and (0) of the signal A. The output of the registers 14 and 15 is output from decoders 16 and 17. When the rotating speed is decreased, the value of the counters 12 and 13 is increased, and the output value of the registers 14 and 15 is also increased. If either one of them indicates the count value 12, an output of an OR gate 18 goes to (1) and a rotation increase signal UP of a disc is outputted. |
