AN-656 Understanding the Operation of a CRT Monitor

Computer technology is going to see major advances in the 1990ss Users will see desk top computers with the computational power of today's super-computerss Even graphics capabilities for sophisticated 3 dimensional modeling and image processing would be available to the average user at a reasonable costt In the area of electronic publishingg users will be able to store video images in the computerr merge the images with text and graphics and produce true color photorealistic hardcopiess Ultra high resolution monitors will be required to make such graphics capabilities availablee Display systems are available in various technologies such as cathode ray tubes (CRTs)) liquid crystal displays (LCDs)) electroluminescent displays (EL)) plasma displayss and light emitting diodes (LEDs)) Howeverr for high resolution monitors the CRT has been and continues to be the technology of choicee Besides its awkward shapee weight and high voltage requirementss the CRT offers many advantages over its competitorss As opposed to other display systems that require a driver for each picture element (pixel)) the CRT requires a single driver to drive the tube's cathode or three drivers for a color displayy CRTs also offer excellent con-trastt luminance and better display resolution than its coun-terpartss Even though the brightness of the CRT's screen is not uniform across the face of the screenn the variation from the center to the corners is gradual and may be unnoticea-ble to most viewerss In the case of LCD or LED displayss howeverr a very tight brightness level matching is required among the adjacent pixelss Continued improvements over the years and declining prices have made the CRT a popular choice for high resolution monitorss The operation of a CRT monitor is basically very simplee A heating element in a CRT heats the cathode and causes it to emit electrons which are accelerated and focused on a phosphor screen by means of high voltage gridss An image (raster) is displayed by scanning the electron beam across the screenn Since the phosphor's luminance begins to fade after a short timee the image needs to be refreshed continu-allyy In order to eliminate flickerr most monitors refresh the screen at a 60 Hz ratee Figure 1 shows a simplified block diagram of a color CRT monitorr The entire circuitry within the monitor can be grouped into three main categoriess video signal processing and amplificationn horizontallvertical deflection and syn-chronizingg and power supplyy As shown in Figure 1 a transmission …