The G420S is a 110Khz monitor capable of 1600 x 1200 at 85 Hz, the pixel clock at 1600 x 1200 at 85Hz is 229.5Mhz.
Don’t confuse “Bandwidth” and “pixel clock”, although related they two completely different things.
Bandwidth is a little complicated and needs some explanation and background in monitor technology.
There are three components that make up the monitors refresh rate. Pixel clock, horizontal scan rate, and the vertical scan rate or “refresh rate”. They are all interrelated.
Monitors draw pixels on the screen one at a time starting in the upper left corner across the screen, then down one line and so on. The time it takes to draw one pixel on the screen is commonly called the video rate, pixel clock or bandwidth. The time it takes to draw one line across the screen is the horizontal scan frequency. Finally the time it takes to draw one complete field “entire screen” is the refresh rate.
Basically, the faster you can draw one pixel on the screen, the faster you can draw a line across the screen, the faster you can refresh the screen.
Almost all monitors on the market today have pixel clock and bandwidth specifications that are sufficient for the resolution the manufacturer recommends. But be careful out there. I see some manufacturers that publish the maximum resolution in BOLD print and the recommended resolution is small print. What they are saying is. Yes the monitor will display at that “BOLD FACE RESOLUTION” however the bandwidth of the monitor is really optimized for the lower “recommended” resolution”.
"Bandwidth" is the range of video frequencies that can be adequately handled by the video amplifier of the monitor, this number can be considerably lower than the pixel clock required for a given timing. The reason for this? The highest fundamental frequency in the analog video signal is one-half the pixel clock, since the fastest thing you can do is to turn alternate pixels on and off. One "on" or "white" pixel followed by one "off" or "black" is required for a full cycle - so the highest fundamental frequency you see is derived from the period of TWO pixels, not one.
There are many ways to measure “Bandwidth” - some relevant, and some not. Without knowing how the manufacturer measured the bandwidth it may not be a very useful specification for comparison purposes.
Jim Witkowski
Chief Hardware Engineer
MonitorsDirect.com
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