| 摘要 |
PURPOSE:To prevent erroneous detection of an index mark signal by generating a detecting window whose width is a prescribed time T2 after a prescribed time T1 from the index signal and taking out only a signal, which is in this detecting window, of the output of an index mark detecting circuit as the index mark signal. CONSTITUTION:A head reproduced output waveform (b) sent from a reproducing circuit is subjected to full wave rectification to go to a waveform (c) and is integrated to go to a waveform (d) and is converted to a pulse (e) by a comparator 27. For the purpose of eliminating a pulse 38 due to noise, both edges of the pulse (e) are detected by a bidirectional monostable multivibrator 29, and a pulse (g) is obtained by delaying the pulse in a delay circuit 30 by a prescribed time Td, and the pulse (e) is latched in a flip flop 31 by this pulse (g) to obtain a pulse (h). For the purpose of taking out only the index mark from a pulse train of the index mark and sectors 1-4, a pulse (j) whose width is the prescribed time T2 is generated after the prescribed time T1 from the index mark signal by monostable multivibrators 32 and 33. The index mark signal is obtained by this detecting window and an AND circuit 34. |
