SERVO CONTROL CIRCUIT OF MAGNETIC RECORDING AND REPRODUCING DEVICE

摘要

PURPOSE:To shorten the pull-in time at starting with simple constitution and without affecting the control characteristics secured in a steady mode, by supplying a signal obtained by stepping down the frequency of a vertical synchronizing signal after the pull-in of phase to a servo system as a reference signal. CONSTITUTION:A gate circuit 40 outputs a vertical synchronizing signal V only when a gate signal G given from a gate signal producing circuit 50 is kept at a high level. A pulse signal S1 and a sample pulse P2 are supplied to the circuit 50. The circuit 50 outputs the signal S1 as the gate signal G for a preiod during which a disk motor 4 is started and then a phase pull-in state is set with the servo control. Then the circuit 40 outputs a signal P0 of a frame frequency is delivered after the signal V of a field frequency is stepped down to just half frequency. The motor 4 is controlled to have phase locking to the signal P0 corresponding to a reference signal. The phase difference time between a pull-in point A and the pulse P2 is increase up to the time of a yield cycle at the most. Thus the pull-in time can be reduced.