portable digital colour television
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Portable Digital Colour Television
April 24, 2012
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.
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
2
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
3
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
1
List of Tables
6.1 Quick Reference Table for the IC . . . . . . . . . . . . . . . . . . 286.2 Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2
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
3
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.
4
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
5
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
6
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
7
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
8
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.
9
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
10
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
11
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.
12
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
13
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:
14
Figure 4.0.2: Elements of a Black & White Picture Tube
15
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
16
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
17
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.
18
Figure 4.3.1: A Composite Video Signal
19
Figure 4.3.2: A Simpli�ed block Diagram Of Colour TV Receiver
20
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
21
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.
22
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.
23
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
24
� 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
28
Figure 6.3.1: Pin Diagram
29
Table 6.2: Ratings
30
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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