| 摘要 |
PURPOSE:To always detect a digital signal having the accurate high and low level periods, by realizing an automatic change of the reference level. CONSTITUTION:The EFM signal obtained through a pickup is supplied to a comparator 1 after its DC component is cut off, and at the same time the reference level signal which is usually set at level 0 for example is also fed to the comparator 1. Therefore the high and low level periods of an EFM signal (a) are decided to the reference level. Thus the EFM digital signal is produced. The reference level signal is delivered through a reference level changing circuit 3 consisting of an up-down counter 4 and a D/A converter 5. The output of the counter 4 is usually set at 0. |
