| 摘要 |
PURPOSE:To demodulate position error signals with high sensitivity and high stability by deriving the position error signals from position pulses of respective tracks when the levels of synchronizing pulses detected from plural servo tracks are below prescribed values. CONSTITUTION:Four kinds of servo tracks are formed in the servo sector provided on a data disc surface, and a synchronizing pulse bit cell and a position pulse bit cell having prescribed phase and polarity are disposed in each track. The index pulses indicating the begining of the servo sectors are detected 12, and a synchronizing pulse detecting circuit 13 is operated by the detected outputs. When the absolute value of the synchronizing pulse is below reference voltage VR, -VR, the operation of a gate circuit 14 operating at prescribed periods is stopped. Position error signals are formed 17-19 by taking the differences in the positive and negative peak holding values of the position pulses obtained from the respective servo tracks in the state that there are no gate pulses. |
