VGA video signal
VGA monitor bandwidth refers to the electron gun scans per second over the total pixel is equal to "horizontal resolution x vertical resolution x field frequency (screen refresh times)." Compared with the line frequency, bandwidth, more comprehensive and more immediate response will monitor performance. But by the above formula to calculate the theoretical value is the level of the bandwidth, in practical applications, in order to avoid attenuation of the signal edges of the image, remain clear around the image, the electron gun is larger than the resolution required in the scan size in the horizontal direction is usually 25% larger vertical direction to a large 8%, so the actual video bandwidth is calculated as "horizontal resolution x125% x vertical resolution x108%", namely "line frame x135%. still above standards, for example: 1024x768x85Hz image mode, the actual bandwidth of about as "1024x768x85x135% = 90.2MHz".
Normal video (AV)
Generally, we believe that ordinary baseband video signal transmission bandwidth 6M. From a technical perspective the monitor, the general picture tube 1MHZ video bandwidth corresponding to 52 lines of horizontal resolution, color monitor displays video bandwidth is 300/52 = 5.76MHZ.
Video bandwidth behalf of a unit of time the amount of information carried by the video signal, VGA video signal and a normal video signal carries 1024x768/85Hz information volume ratio of approximately 15:1.
The bandwidth of the two signals are different, the amount of information carried by different, so when using the AV-VGA AV video signal carrying amount of information can not satisfy the amount of information needed VGA video display, showing the image is not clear, the details can not be displayed screen text, etc. .
These comparisons can be seen in the video signal two technical indicators: Display clarity and signal bandwidth above the normal video to be far behind the VGA video, so the increasing demand for video today, which uses a variety of display systems engineering VGA video Show has become a consensus.