| 摘要 |
PURPOSE:To place an APC circuit in a phase-locked state instantaneously by supplying a reference signal as data on switching from a reproduction mode to a recording mode, and extracting an FG pulse which is in the center of the slanting part of a reference trapezoid wave through a D type FF as a comparison signal. CONSTITUTION:When the reproduction mode is switched to the recording mode, the Q output of the D type FF41 rises to a high level by the FG pulse which is multiplied by two and generated right after the head switching pulse at a terminal 46 rises. The Q output drops to a low level similarly right after the pulse falls. Then, the rising timing of the Q output is in the slanting part of the reference trapezoid wave. This is based upon that the phase of the switching pulse and reference trapezoid wave are constant, that the period of a pulse generated by multiplying the FG pulse is shorter than the time of the slanting part obtained by subtracting the starting time of the slanting part of the trapezoid wave from the falling time of the head switching pulse. In this case, the slanting part of the reference trapezoid wave is in phase with the leading or trailing edge of a recording control pulse in the recording mode. |
