UNLOCK DETECTOR CIRCUIT FOR PLL SYNTHESIZER

摘要

PURPOSE:To make it possible to break the output of an abnormal variable frequency oscillator (VCO) from the instant of an unlocked state by providing a channel switching detector circuit in the unlock detector circuit. CONSTITUTION:Pulse width detector circuit 9 outputs signals while the output pulse width of phase comparator 3 is over a fixed value, and irregular code detector circuit 8 outputs signals when channel selection signal input is a code which does not correspond to regular channels, and channel detector circuit B consisting of delay circuit 12 and disagreement detector circuit 13 outputs signals for a fixed time from the instant of channel switching. Variable frequency oscillator output breaking control circuit 14 causes the output of VCO 5 to pass through switch circuit 11 at a fixed time after outputs of three circuits above are erased. A detector circuit for which a normal unlock detector circuit A is substituted is constituted by these circuits to prevent the abnormal VCO output from being outputted to succeeding stages from the instant when a PLL synthesizer has unlocked.