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How Monitors Work (Page 2/5)

Posted: May 28, 2000
Written by: Tuan "Solace" Nguyen

Pushing and Pulling

After the gun lies what is called the deflection yoke. The deflection yoke controls the electron beams. The yoke has four electromagnets placed equal distances from each other. The yoke can manipulate the beams, pulling and pushing it to light up areas on the phosphorous screen. The yoke actually pulls the beams from left to right on the screen in a sweeping motion. The speed at which this happens is about 50,000 mph - yes, fifty thousand miles per hour.

This process occurs from the upper most left pixel to the bottom most right pixel on the screen. Then the process occurs over again, starting from the top left.

The yoke actually controls varying intensities of the beams while another device control the sweeping motion. The flyback transformer is the device which controls this motion and is composed of winding wires of copper. A low power signal is applied to the flyback transformer's magnetic coil, which creates a magnetic field. When the power source is switched off, the magnetic energy is discharged into a high power output. This output is then transferred to the yolk and provides the power it needs to create the magnetic field used to manipulate the electron beam. When one line on the screen is completely drawn, the transformer discharges. This actually shuts off the electron gun, and the yolk's magnetic field dissipates. The beams then return to the other side of the screen, drop down to the next line and start the process all over again.

Once it has completed the process, the electron beam strikes a phosphorous screen on your monitor. Phosphors glow when hit by electrons. The greater the beam intensity, the brighter the phosphors glow. However, as more energy is shot at the phosphors, they tend to lose brightness over time.

Each line, or row of pixels, is called a raster. If you screen is set to 640x480, you have 480 raster lines. If you're up at 1280x1024, you have 1024 raster lines. Each line contains pixels. For 1024 raster lines, you have 1280 pixels, which gives you the resolution 1280x1024. The speed at which each raster line is drawn is called the horizontal sync. Once a frame has completely been drawn, this is called a refresh. Each pixel only lights up for a split second. Therefore the more raster lines there are to draw, the more quickly the screen has to be drawn in order to keep a constant image. This is called a refresh rate or vertical sync. If your screen is set to 100Hz, this means that the screen is redrawn 100 times a second. Rates 75Hz and above are considered to be less stressful on your eyes. Anything lower and you get that annoying flicker effect. It's easy to detect this by looking off the screen to one side.

Refresh Me

A monitor's pixels are aligned in a fixed grid. Let's say you purchase a high-end monitor that can do a maximum resolution of 1600x1200 (the usual for 19" displays and up), then the monitor contains 1,920,000 pixels. Take the primary trio number -- in this case 1600, and multiply it by the number of raster lines, 1200 and you get 1,920,000 pixels. No monitor can scale to a higher number of pixels, meaning a higher resolution than the physical number of pixels that the screen contains.

Now, when you set your screen to 640x480, you're asking your monitor to resolve 307,200 pixels. Virtually every monitor nowadays can do this, no questions asked. However, once you start entering resolutions like 1280x1024 and above, you're asking your monitor to work harder because it has to hit more pixels -- meaning the beam has to draw more pixels, therefore each frame is drawn slower. Each refresh now takes much longer than before when the screen was only at 640x480. Make sure the monitor you're interested in can do fast refresh rates at high resolutions -- preferably 85Hz at 1280x1024 or 80Hz at 1280x1024 minimum.

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