| 摘要 |
PURPOSE:To prevent a phase locked loop from being malfunctioned at a period with broadcast content by forming the phase locked loop only at the period of synchronizing signal independently of the content of broadcast. CONSTITUTION:A broadcast wave is extracted from a transmitted TV broadcasting wave via a sound sub-carrier eliminating circuit 17. The phase of the broadcast wave and the phase of an output of a reference oscillator 10 are compared by a phase comparator 9. A part of an intermediate frequency is extracted and detected at a synchronizing signal detecting circuit 13 so as to extract the synchronizing signal. A sampling pulse generator 14 generates a sampling pulse by the synchronizing signal. A sampling circuit 15 samples an output of a comparator 9 based on this sampling pulse. The output of the circuit 14 is held by a sampling-hold circuit 16. A voltage controlled transmission station oscillator (VCO) 7 is controlled via a loop filter 8' by the holding value. |
