K.B.H.POLYTECHNIC,MALEGAON CAMP, MALEGAON. Computer Hardware & Maintenance. S.Y.C.M/I.F Guided By :- Mr.K.S.Pawar. Lecturer in Computer Department

Chapter No :- 3 Display devices and its interfacing Mr.K.S.Pawar

Monochrome CRT 1. Mono means one and Chrome means color. 2. They shows their images in one color. Mr.K.S.Pawar

 The video signal from the display card is fed to the monitors video amplifier circuit  Video driver will drive the cathode that means cathode will emit electrons according to the driver s output  The Vsync pulses are fed to the vertical oscillator which generates the required frequency for vertical scanning.  Hsync pulse is fed to the Horizontal oscillator which generates the required frequency for horizontal scanning  The flyback transformer generates the required high Voltage  SMPS provides the different voltages for different circuits Mr.K.S.Pawar

Color monitor – The main difference between colour and monochrome monitor is its CRT – The color CRT has 3 different color Phosphor dots on its CRT face – The phosphor dots are arranged as a triangle (TRIADS ) – It has three electron gun for emitting three electron beam Mr.K.S.Pawar

– Comparisons of CRT and LCD Physical size – CRT monitors are big, bulky and heavy » e.g. An average 17-inch CRT monitor could be upwards of 40 lbs – LCD monitors are small, compact and lightweight » e.g. An average 17-inch LCD monitor is about 15 lbs Price – LCD is more expensive than CRT as one-time purchase but may be cheaper in the long-run due to its longer lifespan and lower power consumption Mr.K.S.Pawar

Disadvantages of CRT – CRT is big in size – It uses more amount of power – Its weight is high So that it is not suited for Laptop computers Mr.K.S.Pawar

LCD Liquid crystal display Invented in 1960 which led the innovation of LCD technology These are organic compounds that exhibit characteristic of both solids and liquids Low power consumption, light weight, and ruggedness Which glow on their own, emitting photons of visible light Mr.K.S.Pawar

They have capability to align their crystalline structure so they can change the polarity of the light that passes through them. If an electric field is applied to these crystals,their alignment can be changed Mr.K.S.Pawar

Technologies used in LCD panels – Super twist – Double super twist – Triple super twist – The twist of the crystals controls the contrast of the screen. Mr.K.S.Pawar

Types of LCD Passive matrix LCD Active matrix LCD(TFT technology) Passive Matrix LCD :- The passive matrix LCD display are used in older and less expensive notebook computers. In passive matrix LCD each cell is controlled by the electrical charges of two transistors, determined by the cells row and column positions on the display. Mr.K.S.Pawar

Active Matrix LCD :- Active Matrix LCD such as those used on most current notebook computer display and all desktop LCD panels. Each cell has its own dedicated transistor behind the panel to charge it and twist the light wave. Active matrix LCDs are depend on thin film transistor(TFT) which are tiny switching transistor and capacitors. Mr.K.S.Pawar

Important Characteristics of LCD  Display resolution The number of distinct pixels in each dimension that can be displayed 1024×768 (XGA, eXtended Graphic Array), 1280×1024 (SXGA, Super eXtended Graphics Array), and 1600×1200 resolution (UXGA, Ultra-eXtended) are the most common display resolutions  Aspect ratio The ratio of the width to height of the display 4:3 for most screens, 16:9 for wide-screen TV Mr.K.S.Pawar

 Color depth Describes the number of colors that can be displayed on a monitor's screen (usually in bit) Each of the three primary colors (red, blue and green) has a number of bits that describe its color depth – e.g. In a “true” color (24-bit color) display, red, blue, and green each has 8 bits or 256 shades (2 8 )  Response time Charging and discharging individual pixels requires a finite time  Dot Pitch The Dot pitch of a CRT is a measurement of the distance between two adjacent dots of same color. As the dot pitch decreases the sharpness of picture increases. Mr.K.S.Pawar

 Video Band width Bandwidth = horizontal pixel X vertical pixel X frame rate  Frame Rate Frame rate is the number of times a screenful of information produced per second.higher the frame rate,less flicker problem we get.  Refresh Rate :- The frequencies at which the monitor rewritten the whole screen is called refresh rate. Mr.K.S.Pawar

 Horizontal scanning Frequency :- The frequency at which the monitor repaints the horizontal lines that make the image is called horizontal scanning frequency.  Vertical scanning frequency :- The frequency at which the monitor repaints the whole screen is called as vertical scanning frequency. Mr.K.S.Pawar

Interlaced Scanning :- In this scanning of a screen is done in two passes.insted of scanning from top to bottom in continuous manner the electron gun skips every next line in first pass. in second pass, it scans the lines missed during first pass. Thus creating the full image in two scans instead of one. First Pass second pass Mr.K.S.Pawar

Non-Interlaced Scanning :- All the lines are scanned or displayed in one pass instead of two passes. Interlaced scanning provides double the refresh rate than non- interlaced scanning. interlaced scanning is used in some raster-scan system and TV sets. Non-interlaced scanning is used mostly in CRT Monitor. Mr.K.S.Pawar

GAS PLASMA 1. The newest entrant in the field of Flat panel display system 2. It uses high power than LCD 3. It uses a grid of X and Y elements that address individual picture elements 4. Each picture element is filled with a gas like XENON,NEON which kept at lower pressure Mr.K.S.Pawar

5. They emits ultraviolet light when we apply high electric potential 6. Rays activate the Red, Green and Blue phosphor dots 7. The draw back is,the time to switch on 8. To overcome this a constant voltage is applied to these cells to keep active 9. This reduces the overall contrast Mr.K.S.Pawar