Transcript gh patel college of engineering and technology

PLASMA TV
2151101: AUDIO-VIDEO SYSTEMS
Guided By:
Prof. Rohit Parmar
Prepared By:
Vishwa Daiya (130110111013)
Hesha Patel (130110111022)
Yesha Patel (130110111062)
G H PATEL COLLEGE OF ENGINEERING AND TECHNOLOGY
Contents:
• Plasma and conduction of charge
• Plasma television screens
• Signal processing in plasma TV receivers
• A plasma colour receiver
• Plasma or LCD-which is best choice
• Performance comparison of plasma and LCD
• Difference between plasma and LCD
• References
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PLASMA AND CONDUCTION OF
CHARGE
• The basic idea of a plasma display is to illuminate tiny colored fluorescent lights to form an
image.
• Each pixel is made up of three fluorescent lights—a red light, a green light and a blue light.
• The variation of intensity of these color lights results in a full range of colors on the display panel.
• The central element in a fluorescent light is plasma, a gas made up of free flowing ions and
electrons.
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• Under normal conditions a gas is mainly made up of uncharged particles where individual
gas atoms have equal number of protons and electrons which balance each other so that the
atom has a net zero charge.
• If many free electrons are introduced into the gas by establishing an electronic voltage
across it, the free electrons collide with the atoms knocking loose other electrons.
• With a missing electron, an atom loses its balance to become an ion with a net positive
charge.
• In the plasma thus created with electric current flowing through it, negatively charged
particles rush towards its positively charged area and positively charged particles move
towards the negatively charged area.
• In this rush, particles are constantly bumping into each other. These collisions excite gas
atoms in the plasma, causing them to release photons of energy in the form of ultraviolet
light.
• The ultraviolet photons cause the release of visible light photons that illuminates the display.
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PLASMA TELEVISION SCREENS
• Xenon or Neon gas atoms are used in plasma screen televisions.
• The gas is contained in hundreds of thousands of tiny cells positioned
between two plates of glass.
• Long electrodes are also sandwiched between the glass plates on both sides
of the cells.
• The address electrodes are behind the cells along the rear glass plate.
• The transport display electrodes which are surrounded by an insulating
dielectric material and covered in a magnesium oxide protective layer are
mounted above the cell along the front glass plate. Both sets of electrodes
extend across the entire screen.
• The display electrodes are arranged in horizontal rows along the screen
and the address electrodes in vertical columns.
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• To ionize the gas into particular cell, the plasma display’s computer charge to intersect at
that cell.
• The computer does so thousands of times in a small fraction each cell in turn.
• When the intersecting electrodes are charged on application, electric current flows through
the gas in the cell.
• The current charged particles which simulate the gas atoms to release ultraviolet photons.
The photons interact with phosphor material coated on the inside wall of the cell.
• A phosphor atom in the cell, one of its electrons jumps to a higher energy level.
• When the electron falls back to its normal level, it releases energy in the form of visible
spots which illuminate the screen.
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• The phosphors in a plasma display give-off color light when they are excited.
• Each pixel is made up of three separate sub-pixel cells with different color (R, G, B)
phosphors.
• Their colors blend to create the overall color of the panel.
• By varying the pulses of current flowing through the cells, the control system can increase
or decrease the intensity of each sub-pixel color to create hundreds of different
combinations of red, green and blue.
• In this way, the control system can produce colors across the entire visible spectrum.
• In television, the control system sends synchronized current pulses in accordance with the R,
G and B video signals obtained on demodulating and processing the received channel signal.
• This results in color pictures similar to those being televised at the transmitting station.
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• MERITS:
1. There is no flicker as all the phosphor excited pixels react at the same time during one
frame of scanning.
2.
There is also no backlight and no projection of any kind. As such, the light emitting
phosphors result in bright pictures with rich colors and wide viewing angle.
• DEMERITS:
1. Though plasma screens are thin, they are heavy and consume lot of power.
2.
These are also fragile and often need professional help to install them.
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SIGNAL PROCESSING IN PLASMA TV
RECEIVERS
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RF INPUT
• The receivers are designed to receive both digital satellite and terrestrial analog and
digital transmissions.
• These are also HD ready, meaning, can receive HDTV transmissions.
• In both 625 line PAL and 525 line NTSC, due to interlaced scanning, there is no picture
information for quite a few lines due to vertical retrace.
• There is a gap of about 49 lines in 625 and 45 in the 525 line systems.
• So the active lines per frame are 576 for-PAL and 480 for the American system.
• These are usually referred as 5761 and 4801 line TV systems.
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TUNER AND IF SECTIONS
• The tuner which is micro-processor controlled is designed to accept all the TV signals.
• Remote Control enables selection of desired transmission and channel.
• The tuner otherwise is as in modern color receivers having features like synthesized
electronic channel selection, auto programming -and remote control of various functions.
• The selected RF input is demodulated and amplified in the tuner in the conventional way to
obtain IF input. From this onwards it is all digital.
• The demodulated and selected IF signal is digitized and then fed to digital signal processing
circuits with the aid of a micro computer.
• Before digitizing, the video and audio IF signals are separated to cater to different
bandwidths and processing requirements.
• The clock frequency for all the digital circuits is derived from the color subcarrier burst
present in the video signal to ensure overall synchronism.
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AUDIO SIGNAL PROCESSING
• The Audio Codec i.e., A/D converter samples the input signal and processes it to enable
one stream output which is input to the audio processor.
• The audio processor, if the signal is stereo sends it through a series of filters that control
stereo balance, tone, loudness and other necessary functions.
• These functions are controlled by signals from the control computer and are based on
user settings: The processed audio signal is converted to analog form by a D/A converter
and on amplification fed to the loudspeakers.
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VIDEO SIGNAL PROCESSING
• A video codec and a video processor produced on VLSI chips are used to process the
video IF signal.
• The video codec converts the signal by a high speed A/D converter into a digital signal
and feeds it to the video processor.
• This separates it into two channels—luminance and chrominance.
• The luminance signal on due processing sets the brightness and contrast of the picture
in accordance with the user's settings.
• The chrominance signal on processing provides R, G, B video components which on
matrixing result in R, G, B video outputs.
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SYNC SIGNALS
• The IF output also feeds into a sync processor.
• It separates horizontal and vertical sync pulses which are used to keep the reproduced
picture in step with the transmitting picture details.
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CENTRAL CONTROL UNIT (CCU)
• The Central Control Unit is in fact a control computer that controls other chips and
translates the user's instructions from a remote controlled transmitter.
• The core of the control computer is a conventional micro-computer supported by a
programmable ROM, control bus and circuits to decode user commands.
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CREATING THE PICTURE
• The most complex job is of interfacing of R, G, B outputs and sync details with the inputs
on the Plasma screen.
• It is done by a computer that is programmed to receive, process and deliver proper
outputs at exact intervals and for predetermined periods to the address lines (columns
and rows) of all, the sub-pixels.
• All inputs to the computer are digital.
• In case of interlaced data, it is first converted to progressive data.
• The computer also controls the size of picture produced and image scanning rate in
conformity with the chosen transmission.
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PLASMA COLOUR RECEIVER
• Features of the receiver are:
1. Motion Optimizer: Clear image of moving objects and figures with no
blurring and noise leaving sharp and vivid pictures on the screen.
2. Color Optimizer: Colors in a specific section can be adjusted without
affecting the surrounding area enabling purest color presentation.
3. Contrast Enhancing: A special circuit provision enhances contrast ratio
which makes dark images more distinctive even against a dark
background.
4. Detail Enhancing: This provision automatically analyzes the section to be
amplified to enable clear and crisp pictures even for delicate details of
spots and lines.
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PLASMA OR LCD-WHICH IS THE BEST
CHOICE
Motion Picture Response Time (MPRT):
• One of the major drawbacks of LCD has been its slower MPRT. This refers to its ability to
remove the displayed image as quickly as possible.
• If the action is slow i.e., MPRT is high, the picture gets blurred and ghost images are seen
on the screen. To further improve the effective refresh rate i.e., MPRT, super sampling is
restored to where the scanning rate is doubled from 50 to 100 per second in PAL and 60
to 120 in NTSC.
• With these and other technological innovations the value of MPRT came down to 15 ms
for LCD versus the value of 8 ms for Plasma and 6 ms that of CRT receivers.
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 Picture Clarity:
• Another drawback that made LCD pictures look fuzzy, lacking contrast was due to leakage of
charge applied to one pixel to un-twist. This partially untwisted pixels around it.
• It is now prevented by using thin film transistors (TFI) around each pixel. TFTs are tiny switching
transistors cum capacitors which hold the charge and not allow it to drift to adjoining pixels.
Thus picture clarity is not affected.
 Contrast Ratio:
• Even in a fully switched-off state liquid crystals allow some back lighting to leak through the
shutters. This limits the contrast ratio to about 1600: 1 as compared to 3000: 1 or even more in
Plasma sets.
• The lack of contrast ratio is most noticeable in darker scenes. Modem LCD receivers use dynamic
backlighting to improve the contrast ratio.
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Color Gamut:
• The accuracy and quality of colors produced in LCD sets depends on the backlighting
source and its ability to evenly produce white light.
• The CCFLs used in earlier televisions were not particularly white and tended to be
strongest in greens.
• These have now been replaced with -LEDs to obtain uniform color reproduction. Since
there is no backlighting in Plasma sets, there is no such problem.
 Viewing Angle:
• Viewing angles are how far away one can sit on either side of the screen before picture
quality is affected.
• With LCD receivers, if sitting at too far an angle, the viewer tends to see some brightness
and color shift. Plasma receivers remain fairly solid at these angles.
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PERFORMANCE COMPARISON OF LCD
AND PLASMA TELEVISIONS
 Picture Quality:
• In general both Plasma and LCD sets produce good quality pictures.
• The LCD TVs improved in this respect after the introduction of LED back lighting and rigorous
control of light transfer to the screen.
 Brightness, Contrast and Colors:
• Plasmas produce higher levels of brightness and contrast levels than the LCDs because the pixels
of their screen structure are either 'ON' or 'OFF' at any given instant.
• However, in LCDs because of back lighting control limitations it is hard to achieve true blacks.
• As such, LCD receivers perform better during day time when there is enough light around.
• On the other hand, Plasma receivers perform better in relatively dark environment and display
black more accurately which means better contrast and more details during dark scenes.
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 Blurring of Images:
• Some LCD screens may have a tendency to blur images particularly during fast moving scenes.
• But with improvements in motion picture response time (MPRT) the effect is seen much less in new LCD receivers.
There is no such problem with Plasma receivers.
 Viewing Angle:
• Viewing angle problem if there in some LCD sets, can be avoided by not sitting too far away from either side of the
screen.
• Plasmas in general are free from this problem.
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 Efficiency and Power Consumption:
• LCDs are relatively inefficient in terms of power use per display size because most of the light that is
produced at the back of the screen is blocked in rear polarizer filters, shutters and color filters before it
reaches the viewer.
• As a result LCD televisions end up with overall power usage similar to CRT receivers of the same size. In
modern LCD sets attempt has been made to address the power use by newer efficient panels, dynamic
lighting and replacing CCFLs with LEDs.
• With this it is claimed that the newer LCD receivers consume power close to or even less than Plasma of
same screen size but of course with a sacrifice of some maximum brightness level.
• Plasma sets are also not very efficient because lot of heat is generated in the screen structure. For example,
SAMSUNG 81 cm screen Plasma TV consumes about 180 watts when operational
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• Weight, Width and Lifespan:
• LCDs are generally lighter with depth around 2 inches than similar size, Plasmas which are about
3 inches deep.
• LCD supporters believe that LCDs have a longer life span than Plasma screens. This may be true
for earlier receivers but the present Plasmas have a life span of more than 20,000 hours of
viewing which is nearly the same as of LCDs.
• Installation:
• Plasmas are heavier, use more power and run hotter than LCD televisions. Therefore, more
planning is required for mounting them on the wall.
• Plasmas are generally best installed by professionals. For LCDs, end users can easily do so
themselves and can even fix the receiver on a suitable stand.
• Screen Size:
• If the need is for a big screen television-50" and above, Plasma continues to be a preference both
in quality and price. LCDs on the other hand generally top out around 52" mark.
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PLASMA VS LCD
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PLASMA
LCD
It has 8 ms MPRT.
It has 15 ms MPRT.
It has higher picture clarity.
It has less picture clarity compared to plasma.
Contrast ratio is more (3000:1 or more).
Contrast ratio is about 1600:1.
It does not have backlighting source.
It depends on backlighting source.
They remain solid at viewing angles.
The viewer tend to see some brightness and colour shift at
viewing angles.
Brightness and contrast levels are higher because the pixels
are either ON or OFF at any given instant.
Brightness and contrast levels are less compared to plasma.
It performs better in dark environment.
It performs better in day time.
It consumes more power.
It consumes less power than plasma of the same size.
It continues to be preferred both in price and quality, 50” and
above.
They are generally around 52” mark.
ANDhigher
TECHNOLOGY
They are about 3 inches deep. G H PATEL COLLEGE OF ENGINEERING
They are generally
up t o 2 inches.
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REFERNCES
• Modern Television Practice: by R.R. Gulati
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THANK YOU !!!
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