Theory - 24 :- LCD vs TFT works?

 History of TFT LCD

Liquid crystal was discovered by the Austrian botanist Fredreich Rheinizer in 1888. "Liquid crystal" is neither solid nor liquid (an example is soapy water).

In the mid-1960s, scientists showed that liquid crystals when stimulated by an external electrical charge could change the properties of light passing through the crystals.

The early prototypes (late 1960s) were too unstable for mass production. But all of that changed when a British researcher proposed a stable, liquid crystal material (biphenyl).

Today's color LCD TVs and LCD Monitors have a sandwich-like structure (see figure below).

LCDs are a type of television screen that uses liquid crystals sandwiched between two sheets of polarizing material.

TFT (Thin‐film transistor) is a field‐effect transistor that is used to build the LCD screen and is embedded in every

pixel, making it faster and giving a better image quality.

What is TFT LCD?

TFT LCD (Thin Film Transistor Liquid Crystal Display) has a sandwich-like structure with liquid crystal filled between two glass plates.

TFT Glass has as many TFTs as the number of pixels displayed, while a Color Filter Glass has color filter which generates color. Liquid crystals move according to the difference in voltage between the Color Filter Glass and the TFT Glass. The amount of light supplied by Back Light is determined by the amount of movement of the liquid crystals in such a way as to generate color.

 

TFT LCD - Electronic Aspects of LCD TVs and LCD Monitors

Electronic Aspects of AMLCDs

The most common liquid-crystal displays (LCDs) in use today rely on picture elements, or pixels, formed by liquid-crystal (LC) cells that change the polarization direction of light passing through them in response to an electrical voltage.

As the polarization direction changes, more or less of the light is able to pass through a polarizing layer on the face of the display. Change the voltage, and the amount of light is changed.

There are two ways to produce a liquid-crystal image with such cells: the segment driving method and the matrix driving method.

The segment driving method displays characters and pictures with cells defined by patterned electrodes.

The matrix driving method displays characters and pictures in sets of dots.

Structure of Color TFT LCD TVs and LCD Monitors

A TFT LCD module consists of a TFT panel, driving-circuit unit, backlight system, and assembly unit.

Structure of a color TFT LCD Panel:

1. LCD Panel
   - TFT-Array Substrate
   - Color Filter Substrate
2. Driving Circuit Unit
   - LCD Driver IC (LDI) Chips
   - Multi-layer PCBs
   - Driving Circuits
3. Backlight & Chassis Unit
   - Backlight Unit
   - Chassis Assembly

It is commonly used to display characters and graphic images when connected a host system.

The TFT LCD panel consists of a TFT-array substrate and a color-filter substrate.

The vertical structure of a color TFT LCD panel.

The TFT-array substrate contains the TFTs, storage capacitors, pixel electrodes, and interconnect wiring. The color filter contains the black matrix and resin film containing three primary-color - red, green, and blue - dyes or pigments. The two glass substrates are assembled with a sealant, the gap between them is maintained by spacers, and LC material is injected into the gap between the substrates. Two sheets of polarizer film are attached to the outer faces of the sandwich formed by the glass substrates. A set of bonding pads are fabricated on each end of the gate and data-signal bus-lines to attach LCD Driver IC (LDI) chips

Driving Circuit Unit

Driving an a-Si TFT LCD requires a driving circuit unit consisting of a set of LCD driving IC (LDI) chips and printed-circuit-boards (PCBs).

The assembly of LCD driving circuits.

A block diagram showing the driving of an LCD panel.

To reduce the footprint of the LCD module, the drive circuit unit can be placed on the backside of the LCD module by using bent Tape Carrier Packages (TCPs) and a tapered light-guide panel (LGP).

How TFT LCD Pixels Work  

A TFT LCD panel contains a specific number of unit pixels often called subpixels.

Each unit pixel has a TFT, a pixel electrode (IT0), and a storage capacitor (Cs).

For example, an SVGA color TFT LCD panel has total of 800x3x600, or 1,440,000, unit pixels.

Each unit pixel is connected to one of the gate bus-lines and one of the data bus-lines in a 3mxn matrix format. The matrix is 2400x600 for SVGA.

Structure of a color TFT LCD panel.

Because each unit pixel is connected through the matrix, each is individually addressable from the bonding pads at the ends of the rows and columns.

The performance of the TFT LCD is related to the design parameters of the unit pixel, i.e., the channel width W and the channel length L of the TFT, the overlap between TFT electrodes, the sizes of the storage capacitor and pixel electrode, and the space between these elements.

The design parameters associated with the black matrix, the bus-lines, and the routing of the bus lines also set very important performance limits on the LCD.

In a TFT LCD's unit pixel, the liquid crystal layer on the ITO pixel electrode forms a capacitor whose counter electrode is the common electrode on the color-filter substrate.

Vertical structure of a unit pixel and its equivalent circuit

A storage capacitor (Cs) and liquid-crystal capacitor (CLC) are connected as a load on the TFT.

Applying a positive pulse of about 20V peak-to-peak to a gate electrode through a gate bus-line turns the TFT on. Clc and Cs are charged and the voltage level on the pixel electrode rises to the signal voltage level (+8 V) applied to the data bus-line.

The voltage on the pixel electrode is subjected to a level shift of DV resulting from a parasitic capacitance between the gate and drain electrodes when the gate voltage turns from the ON to OFF state. After the level shift, this charged state can be maintained as the gate voltage goes to -5 V, at which time the TFT turns off. The main function of the Cs is to maintain the voltage on the pixel electrode until the next signal voltage is applied.

Liquid crystal must be driven with an alternating current to prevent any deterioration of image quality resulting from dc stress.

This is usually implemented with a frame-reversal drive method, in which the voltage applied to each pixel varies from frame to frame. If the LC voltage changes unevenly between frames, the result would be a 30-Hz flicker.

(One frame period is normally 1/60 of a second.) Other drive methods are available that prevent this flicker problem.

Polarity-inversion driving methods. 

In an active-matrix panel, the gate and source electrodes are used on a shared basis, but each unit pixel is individually addressable by selecting the appropriate two contact pads at the ends of the rows and columns.

Active addressing of a 3x3 matrix

By scanning the gate bus-lines sequentially, and by applying signal voltages to all source bus-lines in a specified sequence, we can address all pixels. One result of all this is that the addressing of an AMLCD is done line by line.

Virtually all AMLCDs are designed to produce gray levels - intermediate brightness levels between the brightest white and the darkest black a unit pixel can generate. There can be either a discrete numbers of levels - such as 8, 16, 64, or 256 - or a continuous gradation of levels, depending on the LDI.

The optical transmittance of a TN-mode LC changes continuously as a function of the applied voltage.

An analog LDI is capable of producing a continuous voltage signal so that a continuous range of gray levels can be displayed.

The digital LDI produces discrete voltage amplitudes, which permits on a discrete numbers of shades to be displayed. The number of gray levels is determined by the number of data bits produced by the digital driver.

Generating Colors

The color filter of a TFT LCD TV consists of three primary colors - red (R), green (G), and blue (B) - which are included on the color-filter substrate.

How an LCD Panel produces colors.

The elements of this color filter line up one-to-one with the unit pixels on the TFT-array substrate.

Each pixel in a color LCD is subdivided into three subpixels, where one set of RGB subpixels is equal to one pixel.

(Each subpixel consists of what we've been calling a unit pixel up to this point.)

Because the subpixels are too small to distinguish independently, the RGB elements appear to the human eye as a mixture of the three colors.

Any color, with some qualifications, can be produced by mixing these three primary colors.

The total number of display colors using an n-bit LDI is given by 23n, because each subpixel can generate 2n different transmittance levels.

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Theory - 23 :- What is a Graphics Card? Major Components of a Graphics Card

 What is a Graphics Card?

Graphics card is a hardware which is used to increase the video memory of a computer, and make its display quality more high-definition. It makes the computer more powerful and gives it the capacity to do more high-level works. The quality of the image depends on the quality of the graphics card. It is very much important for gaming and video editing on a PC. Every game needs a graphics memory to start and it depends on the type of the game, and the requirements are mentioned on the game box.

Example :

• Acer predator – Nvidia GTX 1050 4GB Graphics Card.
• Alienware 17 – Nvidia Geforce GTX 1070 8GB Graphics Card.

Both computers have a high power graphics card for better performance.

 

GPU :

• GPU stands for Graphics Processing Unit.
• The power of GPU depends on the model of the GPU.
• The graphics as an external component is attached on a slot known as an expansion slot.
• It is the brain of the graphics card and is what creates the visuals that we see on the monitor.

Types of Graphics Card: 

1. Integrated – The graphics which are built into the motherboard are known as Integrated, are generally used in most laptops, the cannot be easily upgraded.
2. Discrete – It is an external graphics card which is a hardware and added on a motherboard as an extra component. Most people may not need an external graphics card for their work on PC. Basic work like creating files, doing office work, watching movies, listing songs, etc may not need a graphics card. But for the users playing high resolutions games and video editing may need an external component i.e graphics card for their purpose.

 

Features of Graphics Card: 

• Memory – Graphics card carries its own memory. Memory range could be from 128MB to 2GB of memory. We should buy a card with more memory. More RAM equals higher resolutions, more colors on the screen, and the best special effects.
• Multiple Screen support –  Most new video cards have the ability to connect two monitors to one card. This feature is very important for video editing and hardcore gamer craves that extra real estate as well. You can either see two separate Desktops or make the two monitors into one Desktop.
• Gaming And Video Editing –The discrete graphics card is not only for a gamer but those who use high-end video editing software also get help as a high-quality graphics card to reduce the rendering time of an image also give a high-def environment.
• Connection – he graphic card is connected to the monitor using many different ports put the port must be present on both monitor and Graphics card. These are some common ports used to connect graphics card with a monitor.

1. VGA

2. HDMI

3. DVI

Some motherboards have more than 1 expansion slot so we can add more than one  graphics card to make performance better. Many laptops nowadays come with an integrated graphics card in them

Manufacturers of Graphics Card :     

The two main manufacturers of discrete graphics card are –

            1. NVIDIA

            2. AMD

Major Components of a Graphics Card

Here are the most important components of a Graphics Card.

GPU (Graphics Processing Unit)

Graphics Processing Unit or commonly known as GPU is the heart of the Graphics Card. It is the main component of the graphics card where all the graphics processing takes place. Unlike CPU that has only 2 – 16 cores, a GPU processor is made up of hundreds or thousands of small cores or units that runs in parallel to perform complex graphics operations. Nvidia called these cores or processors as Cuda Cores or Shaders and AMD / ATI called them as Stream Processors.

It must be noted that cuda cores and stream processors are not similar in size and operation because of the different GPU architecture used by both these companies i.e. Nvidia and AMD. That means if we have two graphics cards from both Nvidia and ATI with same number of cuda cores and stream processors then we can say that

Cuda Cores ≠ Stream Processors (you cannot equate cuda cores to stream processors in terms of performance as both of them have different architecture)

So here we can conclude that the two graphics card performance will be different even if they have similar memory specs and same number of cuda cores and stream processors

GPU Clock – The speed at which GPU runs is called the GPU Clock or Frequency.

 

Shaders Clock / Frequency – The speed at which these cuda cores / shaders runs are called shaders frequency and it is in synchronization with the GPU clock.

 

Memory

Memory is the place where all the complex textures and other graphics information are stored. GPU fetches the textures from the memory, processes them, send it back to RAM and then it sends it to the RAMDAC and then to your LCD Screen or monitor.

RAMDAC is Random Access Memory Digital to Analog Converter which converts the image to the analog signal and sends them to your Monitor or LCD screen through display cable.

Graphics Cards have different types of memory depending upon the GPU used in the graphics card. The most common type of memories used in graphics cards are GDDR3 and GDDR5 RAM, where G stands for Graphics and DDR stands for Double Data Rate. Graphics Card RAM or Memory is much faster than the Memory used in your Desktop or Laptop.

Internal Interface

The internal interface is the one through which your Graphics Card connects to your motherboard. Older graphics cards uses AGP (Accelerated Graphics Port) interface to connect to the motherboard but now it has been replaced by much faster and efficient PCI Express 2.0 x16 interface. The motherboard should also have the PCI Express x16 slot otherwise you will not be able to use the card. Some motherboards have two PCI Express x16 slots side by side, so that you can use graphics cards connected in SLI or Crossfire mode for increased performance.

Heat Sink and Fan

Heat sink and Fan forms the cooling part of the graphics card, which are used to lower down the temperature of GPU and RAM (in some cards). Heat sink is a passive cooling device that is made up of copper or aluminum and its main purpose is to take the heat away from the GPU and dissipates it in the surroundings. Fan is an active cooling device that blows air onto the heat sink to make heat sink cool down faster so that it can draw away the heat quickly from the components. Some low end graphics cards are equipped with only heat sink but the all the mid and high range ones have both heat sink and fan combination for proper and efficient cooling.

Power Connectors (6-pin)

The power connectors are only present in mid to high range graphics cards because these cards need additional power for their operation. These are 6-pin power connectors and in high range cards there can be two of these connectors present. Low or budget range graphics card do not have these 6-pin power connectors as they do not require that much power for their working and they draw power from the motherboard PCI Express x16 slot only.

If your SMPS or Power Supply does not have the 6-pin power connector then you will need the 6-pin power connector cable as shown in the picture below.

DVI / HDMI / VGA Ports

They forms the external interface of the graphics card. They are used to connect your Monitor or LCD Screen to your Graphics Card by means of relevant cable. Low end graphics card have only VGA and DVI (Digital Video Interface) ports while the high-end ones have both DVI and HDMI (High-Definition Multimedia Interface). Both DVI and HDMI are digital interface but in HDMI the audio signal or sound can be carried by it.

All these components are embedded on the PCB (Printed Circuit Board), which you can say forms the motherboard of a Graphics Card. Besides all these major components, other smaller components like capacitors, diodes, resistors etc. are also present on a graphics card.

 

 

 

 

 

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THEORY - 16 :- SCANNER AND ITS TYPES

Scanner and its Types

The scanner is an input device used to read data or information from different sources. The sources or maybe a written document, graphics, price tag even a photograph, etc. The scanner used to read data from different sources and convert them into a form that can understandable by the computer.

Basically there are two types of scanners

• Optical Scanner
• Optical Reader
• Optical Scanner

An optical scanner also known as a scanner. it used light technology to send input. it is used to read or scan information from printed text and graphics translate them into digital form.

The image scanned by the scanner can be used for different purposes

• It can be printed in the paper
• It can be displayed on the monitor
• It can also be sent to anyone through the mail
• It can also be posted on a web page
• It can also be saved for future used

The image scanner has a resolution of 300 or 600 dpi. The resolution describes the sharpness of an image. If the scanner provides high resolution the image will be more clear and brighter. The quality of the image depends upon the resolution of the scanner.

A large number of dots produce batter quality but also create a huge file sizes.

A professional scanner usually scans at 1200 dpi or higher.

Many scanners also provide optical character recognition (OCR) software is used to read images and convert into digital form and can be edited in a word processor.

Types of Optical Scanner

 

Different types of an optical scanner are as follow

 

Flatbed Scanner 

 

A flatbed scanner is also known as an image scanner. It works the same as a photocopy machine. It inputs one page at a time. The image can be scanned is placed on the glass surface and the scanner reads the image. It mostly used in homes and offices etc.

 

Sheet Fed Scanner

A Sheet fed scanner works the same as flatbed scanner bur documents are inserted on the top of the scanner the same as a fax machine. This design of the scanner decreases the cost and required of space. it also provides automated sheet feeding. However, this feature also prevents the device from scanning bound-book pages or other documents thicker or larger than a sheet of paper.

 

Handheld Scanner

A handheld scanner is a portable type of scanner. It is also known as Half Page scanner because it only scans 2 to 5 inches at a time. These types of scanner are useful in scanning a small amount of data. This scanner is moved by hand over the image to be scanned. These are designed to scan short lines like small web addresses. Some types of handheld scanner used to try to keep the scanner moving in a straight line.

 

Photo Scanners

   

Photo scanner specially designed for scanning large images. These types of a scanner are more expensive than other types of scanners. These types of scanner provide high resolution and provide a high-quality image. Photo scanner usually comes along their own special types of software and also provides an adapter that allows you to work with slides and negatives.  Photo scanners are smaller than other scanners but provide high resolution. A typical photo scanner is the same as a sheet-fed scanner that can scan 3×5-inch or 4×6-inch photographs at 300 dpi or higher resolution.

 

Multi functional Scanner Printer Copier

This is also known as a multi-functional printer; this is basically providing a printer, scanner, and copier all in one. It is useful if you do not need a high resolution of images. They also come with many faxing capabilities. These are mostly used in offices. The software is helpful in scanning an image or documents.

 

Optical Reader

The optical reader used light to read images, documents and convert them into digital form.

 

Types of the optical reader 

Optical Character Recognition (OCR)

Optical character recognition is a technology that used to read handwritten, printed or typewritten characters from documents. It converts the image into a form that the computer can easily understand. It is mostly used in a department store to read price tags by using light.

OCR devices used to read printed characters using an OCR font. The most commonly used OCR font is OCR-A. An OCR device specifies the size and shape of character by detecting a pattern of light and dark.

 

Optical Mark Recognition (OMR)

OMR stands for optical mark recognition. It is also known as the mark sensing device. These used light beam technology to read data or character than convert them into digital signals. These signals send into a computer for further processing. These devices are used to read a character printed in circles and rectangles and printed in a special format. it is mostly used in multiple-choice sheets such as SAT and GRE. The student answers the question by filling the circles. The OMR devices are used to read these circles and evaluate them.

 

Bar Code Scanner

Bar code scanner used a laser beam to read bar codes, Bar codes consist of vertical lines and spaces of different width. Bar code used to represent data that specify the manufacture of products.

 

Different products like pharmacy, supplies, groceries, vehicles, mail, books and magazines contain bar codes. The most popular bar code is POSTNET used by the U.S. Postal services and Universal Product Code is used by retail stores.

 

Magnetic-Ink Character Recognition Reader (MICR)

Magnetic-Ink character recognition reader is used to read the printed text by using magnetized ink. It is mostly used by banks for check processing. Each check has MICR character at the lower left edge.

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