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Portable Digital Colour Television

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Page 1: Portable Digital Colour Television

Portable Digital Colour Television

April 24, 2012

Page 2: Portable Digital Colour Television

Abstract

We have made a portable digital color television using microcontrollers. It has

CRT screen of 14 inches. It uses TDA8305a IC which is an IC for small signal

color television. The microcontroller has AGC, AFC and this micro-controller

will be used to auto-tune the signals and provides optimum output on the screen.

The other special features of the television set are that it supports color and

brightness adjustment. It has the features of picture enhancement, language

options, video gaming etc. other ICs are also used like Chroma IC and Sound

IC.

This portable colour television will have two modes of working i.e. AV and

RF mode. The television set has a tuneable antenna which helps it to receive a

large number of channels from anywhere. The TV provides high picture clarity

and contrast adjustments. It is a low cost set and can be installed very easily.

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Contents

1 Introduction 3

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Basics of a Colour Television . . . . . . . . . . . . . . . . . . . . 41.3 Organisation of the Project Report . . . . . . . . . . . . . . . . . 4

2 Picture Transmission 5

2.1 Black and White Pictures . . . . . . . . . . . . . . . . . . . . . . 52.2 Colour Pictures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3 Television Transmitter 10

3.1 Monochrome TV Transmitter . . . . . . . . . . . . . . . . . . . . 103.2 Colour TV Transmitter . . . . . . . . . . . . . . . . . . . . . . . 103.3 Sound Transmission . . . . . . . . . . . . . . . . . . . . . . . . . 11

4 Television Receiver 13

4.1 Three Colour Theory . . . . . . . . . . . . . . . . . . . . . . . . . 144.2 Sound Reception . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.3 Colour Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.3.1 Colour Video Signal Extraction . . . . . . . . . . . . . . . 174.3.2 Explaination through a Block Diagram . . . . . . . . . . . 18

5 Synchronization 21

5.1 Horizontal Synchronization . . . . . . . . . . . . . . . . . . . . . 215.2 Vertical Synchronization . . . . . . . . . . . . . . . . . . . . . . . 225.3 Horizontal Hold and Vertical Hold . . . . . . . . . . . . . . . . . 23

6 Small Signal Combination IC for Digital Colour TV - TD8305A 24

6.1 General Description . . . . . . . . . . . . . . . . . . . . . . . . . 246.2 Block Diagram (Refer �g 6.2.1) . . . . . . . . . . . . . . . . . . 25

6.2.1 Pin Designation . . . . . . . . . . . . . . . . . . . . . . . 256.2.2 Quick Reference Data (Refer table 6.1) . . . . . . . . . . 27

6.3 Pin Diagram (refer �g. 6.3.1) . . . . . . . . . . . . . . . . . . . . 276.4 Ratings (refer table 6.2) . . . . . . . . . . . . . . . . . . . . . . . 27

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7 Preadjustments in the Colour Television 31

7.1 Convergence Adjustment . . . . . . . . . . . . . . . . . . . . . . . 317.2 Adjustment of the Power Supply . . . . . . . . . . . . . . . . . . 31

8 Implementation 32

9 Future Scope 33

10 References 34

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List of Figures

2.1.1 Simpli�ed cross-sectional view of a Vidicon camera tube & asso-ciated components . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1.2 Path of scanning beam in covering picture area . . . . . . . . . . 72.2.1 Simpli�ed Block Diagram of Colour Camera . . . . . . . . . . . . 9

3.1.1 Elementary Block Diagram Of a Monochrome Television Trans-mitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.0.1 Simpli�ed Block Diagram of Black & White TV Receiver . . . . 144.0.2 Elements of a Black & White Picture Tube . . . . . . . . . . . . 154.0.3 A Colour Picture Tube . . . . . . . . . . . . . . . . . . . . . . . . 164.3.1 A Composite Video Signal . . . . . . . . . . . . . . . . . . . . . . 194.3.2 A Simpli�ed block Diagram Of Colour TV Receiver . . . . . . . 20

6.2.1 Block Diagram representing IC pins . . . . . . . . . . . . . . . . 266.3.1 Pin Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

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List of Tables

6.1 Quick Reference Table for the IC . . . . . . . . . . . . . . . . . . 286.2 Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

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Chapter 1

Introduction

1.1 Introduction

The aim of a television system is to extend the sense of sight beyond its natural

limits and to transmit sound associated with the scene. The picture signal is

generated by a TV camera and the sound signal by a microphone.

The earliest standards were developed for the black and white television sys-

tems. These were 525 line American system, 625 line European system and 819

line France system. Three systems of black and white television have resulted in

three systems of colour television. These are NTSC(National Television Stan-

dards Committee)with 525 line system, PAL (Phase Alteration in Line)with 625

line system and SECAM with 819 line system.

In the 625 line CCIR monochrome and PAL-B color TV systems adopted by

India , the picture signal is amplitude modulated and sound signal frequency

modulated before transmission. The two carrier frequencies are suitably spaced

and their modulation products radiated through a common antenna. As in radio

communication, each television station is alloted di�erent carrier frequencies to

enable selection of desired station at the receiving end.

The TV receivers has tuned circuits in its input section called TUNER. It

selects desired channel out of the many picked up by the antenna. The selected

RF Band is converted to a common �xed IF Band for convenience of providing

large ampli�cation to it.

The amplifed IF signals are detected to obtain video (picture) and audio

(sound) signals. The video signal after large ampli�cation drives the picture

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tube to reconstruct the televised picture on the receiver screen. Similarly, the

audio signal is ampli�ed and fed to the loudspeaker to produce sound output

associated with the scene.

1.2 Basics of a Colour Television

Colour television has all the features of a black and white television alongwith

the additional ability to distinguish the colours. It is based on the theory of the

Additive Colour Mixing where all colours including white can be created by mix-

ing red, green and blue lights. The Colour camera tube provides video signals

for the red, green and blue information. These are combined and transmitted

along with the brightness(monochrome) signal. Each colour television system

is compatible with a corresponding monochrome system. Compatiblity means

that the colour broadcasts can be recieved as black and white on monochrome

recivers. Conversely, colour receivers are able to receive black and white TV

broadcasts.

1.3 Organisation of the Project Report

This project report is divided into 8 chapters in order to provide a complete

insight to the colour television construction. 1st Chapter provides the Intro-

duction to the Colour television. Chapter 2 provides an insight to the picture

transmission for both colour and black & white signals. 2nd and 3rd Chapter

deals with the transmitter and the receiver section of the television. Chapter 4

explains the vertical and horizontal synchronization of the tv signals. Chapter 6

provides all the information about the IC - TD8305A which helps in the proper

synchronization and displaying of the TV signal on the picture tube. Chapter

7 & 8 discusses the Implementation and the Future Scope of the television.

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Chapter 2

Picture Transmission

The picture information is optical in character and maybe thought of as an

assemblage of a large number of tiny areas representing picture details. These

elementary areas into which picture details maybe broken up are known as

"Picture Elements or Pixels", which when viewed together represent visual in-

formation of the scene. Thus, at any instant there are almost an in�nte number

of pieces of information that need to be picked up simultaneously for transmit-

ting picture details. However, simultaneous pickup is not practical because it is

not feasible to provide a separeate signal path(channel) for the signal obtained

from each picture element. In practice, this problem is solved by a method

"Scanning" where conversion of optical information to electrical form is carried

out element by element, one at a time and in a sequential manner to cover the

entire picture. Besides, scanning is done at a very fast rate and repeated a

large number of times per second to create an illusion(impression at the eye)

of simultaneous reception from all the elements, though using only one signal

path.

2.1 Black and White Pictures

In a monochrome (black and white) picture, each element is either bright, some

shade of grey or dark. A TV camera, the heart of which is a camera tube, is

used to convert this optical information into corresponding electrical signal, the

amplitude of which varies in accordance with variations of brightness. Fig. 2.1.1

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Figure 2.1.1: Simpli�ed cross-sectional view of a Vidicon camera tube & asso-ciated components

shows very elementary details of one type of camera tube (vidicon) and associ-

ated components to illustrate the principle. An optical image of the scene to be

transmitted is focused by a lens assembly on the rectangular glass face-plate of

the camera tube. The inner side of the glass face-plate has a transparent con-

ductive coating on which is laid a very thin layer of photoconductive material.

The photolayer has very high resistance when no light falls on it, but decreases

depending on the intensity of light falling on it. Thus depending on light in-

tensity variations in the focused optical image, the conductivity of each element

of photolayer changes accordingly. An electron beam is used to pick-up picture

information now available on the target plate in terms of varying resistance at

each point.

The beam is formed by an electron gun in the TV camera tube. On its way

to the inner side of glass face-plate, it is de�ected by a pair of de�ecting coils

mounted on the glass envelope and kept mutually perpendicular to each other

to achieve scanning of the entire target area. Scanning is done in the same way

as one reads a written page to cover all the words in one line and all the lines

on the page. To achieve this, the de�ecting coils are fed separately from two

sweep oscillators which continuously generate suitable waveform voltages, each

operating at a di�erent desired frequency. Magnetic de�ection caused by the

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Figure 2.1.2: Path of scanning beam in covering picture area

current in one coil gives horizontal motion to the beam from left to right at

uniform rate and then brings it quickly to the left side to commence trace of

the next line. The other coil is used to de�ect the beam from top to bottom

at a uniform rate and for its quick retrace back to the top of the plate to start

this process over again. Two simultaneous motions are thus given to the beam,

one from left to right across the target plate and the other from top to bottom

thereby covering entire area on which electrical image of the picture is available.

As the beam moves from element to element, it encounters a di�erent resistance

across the target-plate, depending on the resistance of photoconductive coating.

The result is a �ow of current which varies in magnitude as the elements are

scanned. This current passes through a load resistance RL , connected to the

conductive coating on one side and to a dc supply source on the other. Depend-

ing on the magnitude of current, a varying voltage appears across resistance RL

and this corresponds to optical information of the picture.

If the scanning beam moves at such a rate that any portion of the scene

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content does not have time to change perceptibly in the time required for one

complete scan of the image, the resultant electrical signal contains true infor-

mation existing in the picture during the time of scan. The desired information

is now in the form of a signal varying with time and scanning may thus be

identi�ed as a particular process which permits conversion of information ex-

isting in space and time co-ordinates into time variations only. The electrical

information thus obtained from the TV camera tube is generally referred to as

video signal (video is Latin for `see').

2.2 Colour Pictures

It is possible to create any colour including white by additive mixing of red,

green and blue colour lights in suitable proportions. For example, yellow can

be obtained by mixing red and green colour lights in intensity ratio of 30 : 59.

Similarly, light re�ected from any colour picture element can be synthesised

(broken up) into red, green and blue colour light constituents. This forms the

basis of colour television where Red (R), Green (G) and Blue (B) colours are

called primary colours and those formed by mixing any two of the three primaries

as complementary colours. A colour camera, the elements of which are shown

in Fig. 2.2.1, is used to develop signal voltages proportional to the intensity of

each primary colour light.

It contains three camera tubes (vidicons) where each pick-up tube receives

light of only one primary colour. Light from the scene falls on the focus lens

and through that on special mirrors.

Colour �lters that receive re�ected light via relay lenses split it into R, G and

B colour lights. Thus, each vidicon receives a single colour light and develops

a voltage proportional to the intensity of one of the primary colours. If any

primary colour is not present in any part of the picture, the corresponding

vidicon does not develop any output when that picture area is scanned. The

electron beams of all the three camera tubes are kept in step (synchronism) by

de�ecting them horizontally and vertically from common driving sources.

Any colour light has a certain intensity of brightness. Therefore, light re-

�ected from any colour element of a picture also carries information about its

brightness called luminance. A signal voltage (Y) proportional to luminance

at various parts of the picture is obtained by adding de�nite proportions of

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Figure 2.2.1: Simpli�ed Block Diagram of Colour Camera

VR , VG and VG (30:59:11). This then is the same as would be developed by

a monochrome (black and white) camera when made to scan the same colour

scene. This i.e., the luminance (Y) signal is also transmitted alongwith colour

information and used at picture tube in the receiver for reconstructing the colour

picture with brightness levels as in the televised picture.

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Chapter 3

Television Transmitter

3.1 Monochrome TV Transmitter

An oversimpli�ed block diagram of a monochrome TV transmitter is shown in

Fig. 3.1.1. The luminance signal from the camera is ampli�ed and synchroniz-

ing pulses added before feeding it to the modulating ampli�er. Synchronizing

pulses are transmitted to keep the camera and picture tube beams in step. The

allotted picture carrier frequency is generated by a crystal controlled oscillator.

The continuous wave (CW) sine wave output is given large ampli�cation be-

fore feeding to the power ampli�er where its amplitude is made to vary (AM)

in accordance with the modulating signal received from the modulating ampli-

�er. The modulated output is combined (see Fig. 3.1.1) with the frequency

modulated (FM) sound signal in the combining network and then fed to the

transmitting antenna for radiation.

3.2 Colour TV Transmitter

A colour TV transmitter is essentially the same as the monochrome transmit-

ter except for the additional need that colour (chroma) information is also to

be transmitted. Any colour system is made compatible with the correspond-

ing monochrome system. Compatibility means that the colour TV signal must

produce a normal black and white picture on a monochrome receiver and a

colour receiver must be able to produce a normal black and white picture from

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Figure 3.1.1: Elementary Block Diagram Of a Monochrome Television Trans-mitter

a monochrome TV signal. For this, the luminance (brightness) signal is trans-

mitted in a colour system in the same way as in the monochrome system and

with the same bandwidth. However, to ensure compatibility, the colour camera

outputs are modi�ed to obtain (B-Y) and (R-Y) signals. These are modulated

on the colour sub-carrier, the value of which is so chosen that on combining

with the luminance signal, the sidebands of the two do not interfere with each

other i.e., the luminance and colour signals are correctly interleaved. A colour

sync signal called `colour burst' is also transmitted for correct reproduction of

colours.

3.3 Sound Transmission

There is no di�erence in sound transmission between monochrome and colour

TV systems. The microphone converts the sound associated with the picture

being televised into proportionate electrical signal, which is normally a voltage.

This electrical output, regardless of the complexity of its waveform, is a single

valued function of time and so needs a single channel for its transmission. The

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audio signal from the microphone after ampli�cation is frequency modulated,

employing the assigned carrier frequency. In FM, the amplitude of carrier signal

is held constant, whereas its frequency is varied in accordance with amplitude

variations of the modulating signal. As shown in Fig. 3.1.1, output of the sound

FM transmitter is �nally combined with the AM picture transmitter output,

through a combining network, and fed to a common antenna for radiation of

energy in the form of electromagnetic waves.

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Chapter 4

Television Receiver

A simpli�ed block diagram of a black and white TV receiver is shown in Fig.

4.0.1. The receiving antenna intercepts radiated RF signals and the tuner selects

desired channel's frequency band and converts it to the common IF band of

frequencies. The receiver employs two or three stages of intermediate frequency

(IF) ampli�ers. The output from the last IF stage is demodulated to recover

the video signal. This signal that carries picture information is ampli�ed and

coupled to the picture tube which converts the electrical signal back into picture

elements of the same degree of black and white.

The picture tube shown in Fig. 4.0.2 is very similar to the cathode-ray tube

used in an oscilloscope. The glass envelope contains an electron-gun structure

that produces a beam of electrons aimed at the �uorescent screen. When the

electron beam strikes the screen, light is emitted. The beam is de�ected by a

pair of de�ecting coils mounted on the neck of picture tube in the same way as

the beam of camera tube scans the target plate. The amplitudes of currents in

the horizontal and vertical de�ecting coils are so adjusted that the entire screen,

called raster, gets illuminated because of the fast rate of scanning.

The video signal is fed to the grid or cathode of picture tube. When the

varying signal voltage makes the control grid less negative, the beam current

is increased, making the spot of light on the screen brighter. More negative

grid voltage reduces brightness. If the grid voltage is negative enough to cut-

o� the electron beam current at the picture tube, there will be no light. This

state corresponds to black. Thus the video signal illuminates the �uorescent

screen from white to black through various shades of grey depending on its

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Figure 4.0.1: Simpli�ed Block Diagram of Black & White TV Receiver

amplitude at any instant. This corresponds to brightness changes encountered

by the electron beam of the camera tube while scanning picture details element

by element. The rate at which the spot of light moves is so fast that the eye is

unable to follow it and so a complete picture is seen because of storage capability

of the human eye.

4.1 Three Colour Theory

The perception of any coloured image by the eye dependes on the sensations

created on the retina which can be divided into three main groups. the eye

senses the actual image by integrating the di�erent colour impressions. This is

called Additive Mixing and forms the basis of any colour television.

In Additive mixing, light from two or more sources obtained either from

independent sources or through �lters can create a combined sensation of a

di�erent colour. Thus di�erent colours are created by mixing pure colours.

These pure colours are Red, Blue and Green. These are the primary colours.

Any colour has three charcaterstics to specify its visual information. These

are:

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Figure 4.0.2: Elements of a Black & White Picture Tube

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Figure 4.0.3: A Colour Picture Tube

� Luminance or Brightness:

This is the amount of light intensity as perceived by the eye regardless of

the colour. In black and white pictures, better lighted parts have more

luminanace than the dark areas. Di�erent colours also have shaded of

luminance in the sense that though equally illuminated appear more or

less bright.

� Hue:

This is the predominant spectral colour of the recieved light. The colour

of any object is ditinguished by its hue or tint. Di�erent hues result from

di�erent wavlengths of spectral radiation and are perceived as such by the

set of cones in the retina.

� Saturation:

This is the spectral purity of the colour light. As colours rarely occur in

the purest form this indicates the amount of other colours present. Thus

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it may be taken as the amount of dilution of the colour by white. A fully

saturated colour has no white in it.

� Chrominance:

The hue and saturation of a colour put together is known as Chrominance.

4.2 Sound Reception

The path of sound signal is common with the picture signal from antenna

to video detector section of the receiver. Here the two signals are separated

and fed to their respective channels. The frequency modulated audio signal is

demodulated after at least one stage of ampli�cation. The audio output from

the FM detector is given due ampli�cation before feeding it to the loudspeaker.

4.3 Colour Receiver

4.3.1 Colour Video Signal Extraction

A color signal conveys picture information for each of the red, green, and

blue components of an image. However, these are not simply transmitted as

three separate signals, because:

� such a signal would not be compatible with monochrome receivers (an

important consideration when color broadcasting was �rst introduced)

� it would occupy three times the bandwidth of existing television, requiring

a decrease in the number of TV channels available

� typical problems with signal transmission (such as di�ering received signal

levels between di�erent colors) would produce unpleasant side e�ects.

Instead, the RGB signals are converted into YUV form, where the Y signal

represents the overall brightness, and can be transmitted as the luminance sig-

nal. This ensures a monochrome receiver will display a correct picture. The U

and V signals are the di�erence between the Y signal and the B and R signals

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respectively. The U signal then represents how "blue" the color is, and the

V signal how "red" it is. The advantage of this scheme is that the U and V

signals are zero when the picture has no color content. Since the human eye

is more sensitive to errors in luminance than in color, the U and V signals can

be transmitted in a relatively lossy (speci�cally: bandwidth-limited) way with

acceptable results. The G signal is not transmitted in the YUV system, but

rather it is recovered electronically at the receiving end.

The two signals (U and V) modulate both the amplitude and phase of the

color carrier, so to demodulate them it is necessary to have a reference signal

against which to compare it. For this reason, a short burst of reference signal

known as the color burst is transmitted during the back porch (re-trace period)

of each scan line. A reference oscillator in the receiver locks onto this signal

to achieve a phase reference, and uses its amplitude to set an AGC system to

achieve an amplitude reference.

The U and V signals are then demodulated by band-pass �ltering to retrieve

the color subcarrier, mixing it with the in-phase and quadrature signals from

the reference oscillator, and low-pass �ltering the results.

4.3.2 Explaination through a Block Diagram

A colour receiver is similar to the black and white receiver as shown in Fig.

4.3.1. The main di�erence between the two is the need of a colour or chroma

subsystem. It accepts only the colour signal and processes it to recover (B-Y)

and (R-Y) signals. These are combined with the Y signal to obtain V R , V G

and V B signals as developed by the camera at the transmitting end. V becomes

available as it is contained in the Y signal. The three colour signals are fed after

su�cient ampli�cation to the colour picture tube to produce a colour picture

on its screen.

As shown in Fig. 4.3.1, the colour picture tube has three guns corresponding

to the three pick-up tubes in the colour camera. The screen of this tube has

red, green and blue phosphors arranged in alternate stripes. Each gun produces

an electron beam to illuminate corresponding colour phosphor separately on

the �uorescent screen. The eye then integrates the red, green and blue colour

informations and their luminance to perceive actual colour and brightness of

the picture being televised. The sound signal is decoded in the same way as in

a monochrome receiver.

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Figure 4.3.1: A Composite Video Signal

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Figure 4.3.2: A Simpli�ed block Diagram Of Colour TV Receiver

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Chapter 5

Synchronization

It is essential that the same co-ordinates be scanned at any instant both at

the camera tube target plate and at the raster of picture tube, otherwise, the

picture details would split and get distorted. To ensure perfect synchronization

between the scene being televised and the picture produced on the raster, syn-

chronizing pulses are transmitted during the retrace, i.e., �y-back intervals of

horizontal and vertical motions of the camera scanning beam. Thus, in addition

to carrying picture details, the radiated signal at the transmitter also contains

synchronizing pulses. These pulses which are distinct for horizontal and vertical

motion control, are processed at the receiver and fed to the picture tube sweep

circuitry thus ensuring that the receiver picture tube beam is in step with the

transmitter camera tube beam.

As stated earlier, in a colour TV system additional sync pulses called colour

burst are transmitted along with horizontal sync pulses. These are separated

at the input of chroma section and used to synchronize the colour demodulator

carrier generator. This ensures correct reproduction of colours in the otherwise

black and white picture.

5.1 Horizontal Synchronization

The horizontal synchronization pulse (horizontal sync HSYNC), separates

the scan lines. The horizontal sync signal is a single short pulse which indicates

the start of every line. The rest of the scan line follows, with the signal ranging

from 0.3 V (black) to 1 V (white), until the next horizontal or vertical synchro-

nization pulse. The format of the horizontal sync pulse varies. In the 525-line

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NTSC system it is a 4.85 µs-long pulse at 0 V. In the 625-line PAL system the

pulse is 4.7 µs synchronization pulse at 0 V . This is lower than the amplitude of

any video signal (blacker than black) so it can be detected by the level-sensitive

"sync stripper" circuit of the receiver.

5.2 Vertical Synchronization

Vertical synchronization (Also vertical sync or VSYNC) separates the video

�elds. In PAL and NTSC, the vertical sync pulse occurs within the vertical

blanking interval. The vertical sync pulses are made by prolonging the length

of HSYNC pulses through almost the entire length of the scan line.

The vertical sync signal is a series of much longer pulses, indicating the start

of a new �eld. The sync pulses occupy the whole of line interval of a number of

lines at the beginning and end of a scan; no picture information is transmitted

during vertical retrace. The pulse sequence is designed to allow horizontal sync

to continue during vertical retrace; it also indicates whether each �eld represents

even or odd lines in interlaced systems (depending on whether it begins at the

start of a horizontal line, or mid-way through).

The format of such a signal in 525-line NTSC is:

� Pre-equalizing pulses (6 to start scanning odd lines, 5 to start scanning

even lines)

� Long-sync pulses (5 pulses)

� Post-equalizing pulses (5 to start scanning odd lines, 4 to start scanning

even lines)

Each pre- or post- equalizing pulse consists in half a scan line of black signal:

2 µs at 0 V, followed by 30 µs at 0.3 V. Each long sync pulse consists in an

equalizing pulse with timings inverted: 30 µs at 0 V, followed by 2 µs at 0.3 V.

In video production and computer graphics, changes to the image are often

kept in step with the vertical synchronization pulse to avoid visible discontinuity

of the image. Since the frame bu�er of a computer graphics display imitates

the dynamics of a cathode-ray display, if it is updated with a new image while

the image is being transmitted to the display, the display shows a mishmash of

both frames, producing a page tearing artifact partway down the image.

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Vertical synchronization eliminates this by timing frame bu�er �lls to coin-

cide with the vertical blanking interval, thus ensuring that only whole frames

are seen on-screen. Software such as video games and computer aided design

(CAD) packages often allow vertical synchronization as an option, because it

delays the image update until the vertical blanking interval. This produces

a small penalty in latency, because the program has to wait until the video

controller has �nished transmitting the image to the display before continuing.

Triple bu�ering reduces this latency signi�cantly.

Two timing intervals are de�ned - the front porch between the end of dis-

played video and the start of the sync pulse, and the back porch after the sync

pulse and before displayed video. These and the sync pulse itself are called the

horizontal blanking (or retrace) interval and represent the time that the electron

beam in the CRT is returning to the start of the next display line.

5.3 Horizontal Hold and Vertical Hold

The lack of precision timing components available in early television receivers

meant that the timebase circuits occasionally needed manual adjustment. The

adjustment took the form of horizontal hold and vertical hold controls, usually

on the rear of the television set. Loss of horizontal synchronization usually re-

sulted in an unwatchable picture; loss of vertical synchronization would produce

an image rolling up or down the screen.

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Chapter 6

Small Signal Combination IC

for Digital Colour TV -

TD8305A

6.1 General Description

The TD8305A is a TV sub-system circuit, for colour television receivers with

the following features:

� Vision IF ampli�er with synchronous demoldulator

� Automatic Gain Control(AGC) detectorsuitable for negative modulation

� AGC Tuner

� Automatic Frequency Control(AFC) circuit with samle-and-hold

� Video preampli�er

� Sound IF ampli�er and demodulator

� DC volume control or seperate supply for starting the horizontal oscillator

� Audio preampli�er

� Horizontal synchronization circuit with two control loops

� Vertical Synchronization (divider system) and sawtooth generation withautomatic amplitude adjustment for 50 & 60 Hz

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� Transmitter identi�cation (mute)

� Generation of sandcastle pulse

6.2 Block Diagram (Refer �g 6.2.1)

6.2.1 Pin Designation

1. AGC Takeover / X-Ray Protection

2. Vertical ramp generator

3. Vertical drive

4. Vertical feedback

5. Tuner AGC

6. Ground

7. Main Supply Voltage

8. Vision IF Input

9. Vision IF Input

10. IF AGC

11. Volume Control / Start horizontal Oscillator

12. Audio Output

13. Sound Demodulator

14. Sound IF Decoupling

15. Sound IF Input

16. Ground (for some critical parts)

17. Video Output

18. AFC Output

19. AFC S/H, AFC Switch

20. Vision Demodulator Tuned Circuit

21. Vision Demodulator Tuned Circuit

22. Coincidence Detector

23. Horozontal Oscillator

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Figure 6.2.1: Block Diagram representing IC pins

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24. First Phase Detector

25. Sync Seperator

26. Horizontal Drive

27. Sandcastle Output / Horizontal Flyback Input

28. Second Phase Detector

6.2.2 Quick Reference Data (Refer table 6.1)

6.3 Pin Diagram (refer �g. 6.3.1)

6.4 Ratings (refer table 6.2)

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Table 6.1: Quick Reference Table for the IC

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Figure 6.3.1: Pin Diagram

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Table 6.2: Ratings

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Chapter 7

Preadjustments in the Colour

Television

7.1 Convergence Adjustment

Convergence adjustment in the colour television sets is one of the most impor-tant adjustment in order to get a desired colour of the image at the screen. Itis done in order to focus all the three electron beams of the primary colours i.ered, green and blue at a particular spot on the phosphor screen.

We have done these adjustments in our television by rotating the magnetbars at the back of the picture tube in the desired directions such that thefocusing of the electron beams is proper till the true colour of the image isfound.

7.2 Adjustment of the Power Supply

In India, the AC power supply available is 220 V. In order to provide an appro-priate voltage supply to the circuitary of the television, we need to convert the220 V AC to 110 V AC supply.

This adjustment is done with the help of a preset(generally a variable resis-tance) in the portable colour television.

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Chapter 8

Implementation

The portable digital television can be used in various di�erent applications:

1. Educational purposes:

Due to its small size and low cost it can easily be used as a model before thestudents in order to make them familiar with hardware aspect of television.It will help them to relate the theory to the actual working of the television.

2. Closed Circuit Television:

The portable television can be used for CCTV applications where thebudget available is quite less.

3. Rural Areas:

In the areas where there is usually a reception problem and the people arenot able to a�ord bigger screen TV sets, the portable Tv sets can act asa substitute. In rural areas where there are poor people as well as poorreception of private channels portable television can be used.

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Chapter 9

Future Scope

The digital television set can be used in various areas in the future.

1. It can be used in rural areas where expensive tv sets cannot be a�orded.This can be a widespread use of the set.

2. It can used with rechargeable batteries too so that even without electricitysupply one can get uninterrupted reception.

3. The features of the television set can be enhanced by incorporating theHDTV features in it.

4. The additional features of audio reception only can be added to this setso that it can act as a FM receiver too.

5. It can have a USB port through which it can be connected to other digitaldevices.

6. The Digital TV preadjustments used in our project can be converted intocoding operated preadjustments.

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Chapter 10

References

� Monochrome & Colour Television - R.R. Gulati

� Television & Radar Engineering - K.K. Sharma

� National Panasonic CTV Service Manual for model no. 2120

� Funda Manual

� http://en.wikipedia.org/wiki/Digital_television

� http://www.bg-electronics.de/datenblaetter/Schaltkreise/TDA8305A.pdf

� http://www.etsi.org/deliver/etsi_tr/101100_101199/101190/01.03.01_60/tr_101190v010301p.pdf

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