| 摘要 |
PURPOSE:To attain quick normal locking state even when a pseudo locking is obtained by using a part of a reproducing signal to form an error signal thereby applying the signal to a DC level control means when a decision circuit decides the pseudo locking state from the level of an input signal of an A/D converter. CONSTITUTION:When the state reaches the pseudo locking state, e.g., the level is positive, the level taken for the input signal to the A/D converter 4 is shifted positively to the 1st bit threshold value V1. Thus, the output voltage of a low pass filter 22 being a mean value of the input signal of the A/D converter 4 is shifted positively and exceeds a reference voltage V+ of the voltage comparator 23. Thus, a decision circuit 20 is as pseudo locking and outputs '0' as a decision signal 21. As a result, the 1st bit output B1 is selected by a switching circuit 19 and an output signal 8 is obtained, the output voltage of a low pass filter 11 averaging it has a larger positive value than the output voltage of the normal locking, the output voltage of the DC amplifier 2 is drawn largely toward the negative level by negative feedback control. As a result, a pseudo locking is released and normal locking is attained.
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