| 摘要 |
PROBLEM TO BE SOLVED: To prevent erroneous charging incurred while viewing charged broadcasting signals. SOLUTION: A set top box 2 receives charged broadcasting data, executes a decoding processing and outputs video signals to a monitor 8. A signal detection means 11 detects the video signals displayed on the monitor 8 by using magnetic flux leakage generated in the deflection coil of the monitor 8 for instance and a synchronization component extraction circuit 13 extracts horizontal synchronizing signals from the input video signals and supplies them to a phase comparator circuit 14. In the meantime, a synchronizing signal extraction circuit 10 extracts horizontal synchronizing signals from the video signals supplied from the STB(set top box) 2 and supplies them to the phase comparator circuit 14. The phases of the two input signals are compared and thereafter, synchronization is judged from the phase compared result by a synchronization judgement circuit 15. When asynchronization is judged, a charging system part 9 judges that a charged program is not viewed, interrupts charging and stops the output of the STB 2. |
