| 摘要 |
<p>PURPOSE:To shorten a lock-in time required for tracking by changing temporarily a circulation order when a phase of a circulation order of frequency of the third signal is different greatly from a circulation order of the frequency of a tracking signal. CONSTITUTION:When the frequency of an automatic frequency control oscillator 23 is denoted as f1, and frequency of a band pass tracking signal is denoted as f2 or f4, signal components of f2-f1=15KHz (the first signal) and f4-f1=45KHz (the second signal) are obtained in an output of a mixer 24. In case when the frequency of the oscillator 23 is f1 or f2, and the frequency of the tracking signal is f3 or f4 in accordance with said frequency, a signal component of -f3-f1-= 60KHz, or -f4-f2-=30KHz (both are the third signal) is obtained. The third signal is detected, sets a TR34 to an on-state, and an oscillation control switch 36 is switched to a contact 36C. Therefore, as for the frequencies of the oscillator 23, f1 and f3, or f2 and f4 are replaced, and tracking can be taken instantaneously. That is to say, when the oscillation frequency of the oscillator 23 is made to coincide with the frequency of the tracking signal by which a head 21 is reproduced at the present time point, the lock-in time of a tracking error is shortened.</p> |
