| 摘要 |
PROBLEM TO BE SOLVED: To detect presence of a synchronizing signal for each system in a monitor with a plasma display panel (PDP) mounted thereon, to which a video signal of the NTSC, PAL, and SECAM system is given. SOLUTION: A video signal Vi of each system is inputted to a horizontal synchronizing separator circuit section 1, by which a horizontal synchronizing signal is separated. The separated horizontal synchronizing signal is inputted to a synchronization detection section 2. This synchronization detection section 2 outputs a signal showing the synchronization state when the frequency of the horizontal synchronizing signal and an oscillator output frequency are the same. An output detection section 6 detects a signal outputted from the synchronization detection section 2 and showing the synchronization state. When the detection is made, a changeover control section 7 keeps a current throwing state and when not made, the changeover control section throws the current position to other oscillator side. According to this changeover, the synchronization detection section 2 outputs the signal above in the synchronization state and outputs a signal showing a video no input state when in an asynchronous state. Thus, the presence of an input video signal is detected. |
