| 摘要 |
PURPOSE:To surely prevent a malfunction with simple configuration with respect to the malfuction preventing circuit for phase locked loop circuit to prevent the phase locked loop circuit from being locked at any frequency excepting for the desired frequency. CONSTITUTION:A phase locked loop circuit is provided to frequency divide the output signal of a voltage controlled oscillator (VCO) 1 with a frequency divider 2, to compare the phase with the output signal of a synthesizer 3 by using a phase comparator 4, to pass a phase comparison output signal through low-pass filter 5 and an amplifier 6 and to define it as the control voltage of the VCO 1. Further, a malfunction preventing circuit 9 is provided to get out of an erroneous frequency pullNn state by resetting the control voltage of the VCO 1 at a prescribed value such as an initial value or considerably changing the control voltage in the manner of a pulse when a phase lock state is detected by a lock detection part 7 and R,& a correction judge part 8 judgesNthe lock frequency is wrong. |
