| 摘要 |
PURPOSE:To prevent the partial deterioration of a cathode-ray tube by displaying a video signal at the range narrower than the displaying range of the cathode-ray tube and adding a signal modulated at least in a vertical direction for an area except the video signal. CONSTITUTION:A brightness signal generating circuit 2 generates a brightness level, a gate pulse generating circuit 3 generates a gate pulse D corresponding to the period without a video signal by an output video signal B from a horizontal pulse C synchronized with an input signal and a gate circuit 8 gates the brightness signal. On the other hand, from the horizontal pulse C and a vertical pulse E synchronized to an input signal by a modulating signal generating circuit 4, a frequency-dividing pulse F of the horizontal pulse C synchronized with the vertical pulse E is generated and through an inverting circuit 5, further, a switching circuit 6, the brightness level of the brightness signal generating circuit 2 is modulated. The modulated brightness signal is inputted through the gate circuit 8 to a synthesizing circuit 9, synthesized with the video signal B and a synthetic video signal G is obtained. |
