| 摘要 |
PURPOSE:To absorb a DC reproduction error due to the fluctuation in the mark rate or same code consecution by adopting the circuit constitution such that only a peak after DC recovery is not detected from a signal subjected to DC fluctuation in an identification circuit but a true amplitude is always detected and its median is given as a threshold level. CONSTITUTION:A peak value detection circuit 7 and a threshold level control circuit 8 are provided. At first a signal after DC recovery is given to a maximum value detection circuit 7 and a minimum value detection circuit 71. After the maximum and minimum value are detected in each circuit, the amplitude is detected by calculating the difference. Then the median of the amplitude is formed from the amplitude by a control circuit 80 and given as a threshold level of an identification circuit 3. Since both the maximum and minimum values are fluctuated in the same direction even when a DC level of an input signal is fluctuated in addition to the fluctuation of the amplitude of the input signal, the threshold level is fluctuated by the same level and the level is always set to 1/2 of the input amplitude. Thus, the amplitude information is always detected against the fluctuation in the mark rate or same code consecution. |
