| 摘要 |
PURPOSE:To improve reliability by preventing a phase-detection type killer circuit from malfunctioning by putting an automatic phase control system into operation even in recording. CONSTITUTION:In reproduction, since switch circuit 6 is OFF, a killer signal is outputted from killer phase detecting circuit 9. In recording, crystal oscillator 2 is stopped to turn circuit 6 ON. At this time, the output of variable frequency crystal oscillator 5 is inputted to terminal (b) of -90 deg. phase-shifting circuit 3. At the point in time, a signal phase is set to phi1, and consequently the signal and a received burst signal (phase phi2) are inputted to APC phase detecting circuit 1, which bears the relation of phi1=phi2-90 deg. by locking. Then, this signal is passed through phase-shifting circuit 3 to set the phase of point (a) to phi1+90 deg. and detecting circuit 9 makes a phase comparison to the received burst signal as well as in reproduction to output a needed killer signal. Thus, the AFC system is put into operation even in recording, so that while malfunction due to noises, etc., is prevented, the reliability can be improved. |
