| 摘要 |
<p>PURPOSE:To speed up the lead-in time of a video head at the time of tracking control by allowing the video head to generate residual reference pilot signals successively from a reference pilot signal corresponding to a track to be successively scanned. CONSTITUTION:A timing generating circuit 13 switches reference pilot selecting signals Sel 1, 2 at the prescribed timing and outputs the switched signal to a reference pilot selecting circuit 12. The circuit 12 controls a reference pilot generating circuit 11 to supply reference pilot signals f1-f4 to a balanced modulator 2 correspondingly to four-divided times T1-T4. Consequently, a difference frequency signal is outputted from a differential amplifier 7. At the time of inputting the difference frequency signal, a waveform shaping circuit 15 forms a track discriminating signal 1000 and outputs the signal 1000 to a speed deciding/track discriminating logic circuit 16. The circuit 16 outputs a reference pilot specifying signal 700 to the circuit 13. The circuit 13 outputs the signal Sel 1 or 2 to the circuit 12 on the basis of the signal 700. Consequently, the circuit 11 supplies the reference pilot signals with four frequency levels successively to the modulator 2 on the basis of the specified signal 700.</p> |
