| 摘要 |
PROBLEM TO BE SOLVED: To prevent the erroneous judgment of a stereo mode and an SAP mode by a USA sound multiple system. SOLUTION: When a PLL circuit 103 is judged to be locked to the carrier of a video signal, the PLL locking detection part 102 of a VIF/SIF demodulation circuit 13 outputs a PLL locking detection signal to a judgement circuit 14. The demodulation part 101 of the VIF/SIF demodulation circuit 13 outputs a sound detection signal to stereo LPF 15 and SAPBPF 16. When the judgment circuit 14 continuously receives the PLL locking detection signal for a prescribed time, it outputs a judgment control signal to a stereo discrimination part 17 and an SAP discrimination part 26. While the judgment control signal is inputted from the judgment circuit 14, the stereo discrimination part 17 judges the presence or absence of a differential signal inputted from stereo BPF 15. While the judgment control signal is inputted form the judgment circuit 14, the SAP discrimination part 26 judges the presence or absence of the SAP signal inputted from SAPBPF 16 or SAPLPF 25.
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