What is a CRT monitor?

CRT displays (the scientific name "cathode ray tube") is such a device, it mainly by the electronic gun (electron gun), deflection yoke (deflection coils), shade mask (Shadow mask), high pressure graphite electrode and phosphor coating (phosphor) And the glass shell is composed of five parts. One of the most impressive is the glass shell, also known as a fluorescent screen, because its inner surface can display rich color images and clear text. How does a CRT monitor use the three-color principle in it? Of course, it is not directly to the three primary colors on the screen, but by the electron beam to control and performance.

How the electron gun works

This depends first on the phosphor layer, on the screen coated in a certain way tightly arranged red, green, blue phosphor point or fluorescent noodles, called phosphor unit, adjacent red, green, blue phosphor unit for a group, the scientific name called pixels. Each pixel has a red, green, blue (R, G, B) three-color, according to what we have just said the three-color theory, which has the formation of the basis of ever-changing colors. However, how to mix these three primary colors into a rich color?

We solve the problem with an electron gun (electron gun), yes, the electron gun is like a pistol, it can be fired, but it's not a bullet, it's a very high-speed electron beam. Its working principle is by the filament plus hot cathode, cathode emission electrons, and then in the acceleration of the polar field, by focusing on the very thin electron beam, under the anode high-pressure action, to obtain huge energy, at a very high speed to bombard phosphor layer. The target of these electron beam bombardment is the three primary colors on the phosphor screen. To this end, the electron gun emitted by the electron beam is not a bunch, but three bundles, respectively, they are computer graphics card R, G, b three color video signal voltage control, to bombard their own phosphor units. Stimulated by high speed electron beam, these phosphor units emit three kinds of light, red, green and blue respectively. According to the color mixing method (the method of mixing three base colors at three dots adjacent to the same surface simultaneously) produces rich color, this method has the same effect as the direct blending method by using the characteristic that people's eyes are less discriminating after a certain distance. This method can produce different colors of pixels, and a large number of different colors of pixels can form a beautiful picture, and constantly changing the screen becomes a movable image. Obviously, the more pixels, the clearer and finer the image, the more lifelike it is. But how do you use an electron gun to inspire tens of thousands of pixels at the same time to glow and form a picture?

How the monitor is scanned

Understand the three primary colors, smart You must think, you can use such a principle to make color display. Yes, our colorful CRT display today is made out of this three-color principle. As we mentioned just now, the choice of tri-color is arbitrary in principle, but through experimental research, we found that the human eye to the red, green, blue Three colors of the most sensitive response (human eyes see the color is due to different wavelengths of light caused by the naked eye of the three wavelengths of the feeling is particularly strong), and their color range is relatively wide, With these three colors can be free to match most of the natural color, so in the CRT display, choose red, green, blue three colors as three primary color, but also with R, G, b three letters to express. Now the question is, how can we show the light of these three primary colors, we need an electromechanical device to perform this process.

Yes, because there are a large number of neat and orderly pixel needs to be stimulated, it is inevitable that the regular electronic gun scan movement to appear efficient, usually achieve a lot of scanning methods, such as linear scan, round scan, spiral scan and so on. Among them, the linear scan can be divided into line-by-row scanning and interlaced scanning two kinds, I believe we are often heard, in fact, in the CRT display system both have adopted. A progressive scan is a more advanced way of scanning an electron beam from left to right on one line of the screen. In interlaced scanning, the scan of an image is not done in one field cycle, but is done by two field cycles. Scanning all odd rows in the previous field cycle, called an odd-field scan, scans all even rows in the latter field period, called an even-number field scan. Whether a line-by-row scan or interlaced scan, in order to complete the scan of the entire screen, the scan line is not completely horizontal, but slightly tilted, so that the electron beam is not only horizontal direction of movement, but also for vertical direction. The former form a line of scans, called row scans, the latter form a picture of the scan, called field scan.

With a scan, you can form a screen, however, in the process of scanning, how can you guarantee that three electron beams accurately hit each pixel? This is the use of the Shadow Mask (Shadow mask), its position is probably behind the screen (from the screen front) about 10mm, The thickness is about 0.15mm thin metal barrier plate, it has many small holes or fine grooves, they and the same group of phosphor unit namely pixel corresponds. Three electron beams passing through small holes or grooves can only hit the corresponding phosphor units in the same pixel, so that we can ensure that the color is pure and correct convergence, so we could see the clear image.

As for the continuous sense of the screen, it is determined by the speed of the field scan, the faster the field scan, the more the single image formed, the smoother the screen. And how many times per second field scan is usually a measure of the quality of the screen, we usually use frame frequency or field frequency (Hz, Hertz) to indicate that the larger the frame frequency, the more continuous image. We know that 24Hz field frequency is to ensure that the image active content of the continuous feeling, 48Hz field frequency is to ensure that the image shows no flicker of the feeling, these two conditions are met, to display a good image. In fact, this is similar to the formation principle of animation, a picture of a quick flash of people's eyes, on the formation of a continuous screen, it becomes animation.