How much do you know about VGA video signal and AV video signal?

 

    VGA video signal

 

    The bandwidth of a VGA display refers to the total pixels scanned by the electron gun per second, which is equal to "horizontal resolution x vertical resolution x field frequency (number of screen refreshes)". Compared with the horizontal frequency, the bandwidth is more comprehensive and more directly reflects the performance of the display. However, the horizontal bandwidth calculated by the above formula is only a theoretical value. In practical applications, in order to avoid signal attenuation at the edge of the image and keep the image around clear, the scanning capability of the electron gun needs to be larger than the resolution size. The horizontal direction is usually 25% larger than the vertical The direction is 8% larger, so the actual video bandwidth calculation formula is "horizontal resolution x 125% x vertical resolution x 108%", that is, "line frame x 135%. Still using the above standard as an example: 1024x768x85Hz image mode, the actual bandwidth "1024x768x85x135% = 90.2MHz".

 

    Normal Video (AV)

 

    Generally we think that the baseband transmission bandwidth of ordinary video signals is 6M. From the technical point of view of the monitor, the 1MHZ video bandwidth of a general picture tube corresponds to the horizontal definition of 52 lines, and the video bandwidth displayed by a color monitor is 300/52 = 5.76MHZ.

 

    The video bandwidth represents the amount of information carried by the video signal per unit time. The ratio of the VGA video signal 1024x768 / 85Hz to the amount of information carried by ordinary video signals is about 15: 1.

 

    in conclusion

 

    The two types of signals have different bandwidths and carry different amounts of information. Therefore, when using AV-VGA, the amount of information carried by the AV video signal cannot meet the amount of information required for VGA video display. .

 

    The above comparison can be seen in the two major technical indicators of video signals: display clarity and signal bandwidth. Ordinary video is far behind VGA video. So today, video requirements are increasing, and various display system projects use VGA video. The display has become a consensus.