Video signal mixing unit for simultaneously displaying video signals having different picture aspect ratios and resolutions

Claim 1

A video signal mixing unit for simultaneously displaying a first video signal and a second video signal transmitted from a first video information source and a second video information source respectively on a single CRT display device, said first video information source having a first aspect ratio and a first resolution and being controlled by a first pixel clock and a first synchronizing signal, said CRT display device being controlled by said first pixel clock and said first synchronizing signal, said second video information source having a second aspect ratio and a second resolution different from said first resolution and being controlled by a second pixel clock and a second synchronizing signal, said video signal mixing unit comprising: video buffer means connected to said second video information source for storing said second video signal; third video pixel clock generating means connected to said first and second video information sources for generating, on the basis of said first and second aspect ratios, said first and second resolutions and a horizontal display time of one scanning line of said CRT display device, a third pixel clock with which said second video information source can be displayed on said CRT display device with said second aspect ratio; and video signal selecting means connected to said first video information source, and connected to said video buffer means and said third pixel clock generating means for selectively outputting said first video signal sent from said first video information source at a rate of said first pixel clock and said second video signal transferred from said video buffer means at a rate of said third pixel clock.