| 摘要 |
PURPOSE:To perform stable speed servo by making the maximum or minimum inversion interval of the reproduced signal, a reference value, and pull-in a linear speed constant, then by subjecting speed servo with a signal which synchronizes with a playback signal fed from a PLL. CONSTITUTION:After the rotational speed of a disk is pulled in a specific linear speed, the PLL of a frame synchronizing signal detecting circuit 4 is phase- locked with a playback signal, and a frame synchronizing signal is detected in the reproduced signal, then its detected output D goes to ''H''. Consequently, a swtiching circuit 8 obtains a signal supplied to an input terminal C2 or C3, i.e., signal SFP having the specified period synchronized with the reproduced signal which is formed basing on the output of PLL. In this case, the signal SFP is obtained from the switching circuit 8 regardless of whether the output of an NAND gate 9B is at H or L. Therefore, a counter 9A is cleared invariably by this signal SFP. |
