Transcript Chapter 23 - Goodheart

Chapter 23
Television and Video
Display Units
Objectives
• Explain the steps in the transmission of a
television signal.
• Discuss the scanning process.
• Identify circuits in both black-and-white
and color television receivers and explain
their functions.
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Objectives
• Identify the size and makeup of a
television channel.
• Discuss a variety of television innovations,
including video cassette recorders, remote
control, and satellite television.
• List the benefits of HDTV, as compared to
analog television.
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Objectives
• Explain the difference between
multicasting and datacasting.
• Discuss the compression technique of
MPEG2.
• Discuss the various flat-panel
technologies.
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Television Signals
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Television cameras
Scanning
Composite video signals
Basic CRT controls
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Television Cameras
• Picture elements
• Camera “sees” a scene as a combination
of picture elements
• Photoelectric cells in the camera respond
to scene by producing a voltage
• Voltages are amplified for AM carrier wave
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Image Orthicons
• Varying degrees of light cause electrons to be
emitted on the target side of the cathode and
form an electronic image
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Scanning
• Electron beam responds to point-to-point
brilliance of a picture
• Interlace system used in United States has
525 scanning lines
– Scans odd numbered lines of pattern first, and
then scans even numbered lines
• Fields
• Frames
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Scanning (Cont.)
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FCC sets frame frequency
30 frames per second
Horizontal deflection oscillator
Vertical deflection oscillator
The beam scans as it moves left to right
Beam must return to top to scan again
after reaching the bottom
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Scanning (Cont.)
• Deflection yoke
• Synchronization
(sync) pulse
• Horizontal hold
• Vertical hold
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Composite Video Signals
• All video signals are
formed the same way
• FCC sets standards
• Contain picture and
sound information
– Video is AM signal
– Audio is FM signal
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Composite Video Signals (Cont.)
• First 75% of
amplitude transmits
video information
• Remaining 25% is for
sync pulses
• Higher amplitudes of
video information
produce darker areas
in the picture
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Composite Video Signals (Cont.)
• Screen is driven back to the pedestal, or
blanking level
• Sync pulse is sent in infrablack region for
oscillator synchronization
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Basic CRT Controls
• CRT is used to
produce images in
television sets
• Bias controlling
current is brightness
control
• Raster can be seen
when TV is on a
vacant channel
(RCA)
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Review
How does a television camera transmit
video to television?
The photoelectric cells in a camera
produce voltages. The voltages are
amplified and used for modulation of the
AM carrier wave, which is then transmitted
to the home receiver
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Review
What is scanning?
The point-to-point examination of a picture
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Review
How many scanning lines are used in the
scanning system of the United States?
525
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Review
What is a raster?
The lines on a TV screen when a vacant
channel is showing
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Television Receivers
• Black-and-white television receivers
• Color television receivers
• Television channels
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Black-and-White Television
Receivers
• RF amplifier stage
– Similar to function in superheterodyne radio
– Provides constant gain and selectivity
– Video signal amplified and fed to mixer
• Mixer stage
– Intermediate frequency is produced
– Fine-tuning
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Black-and-White Television
Receivers (Cont.)
• Tuner, or front end
– Put together in the factory
– No adjustments should be made on these
without thorough understanding
• PIX-IF amplifiers
– Amplify broad band of frequencies
– Voltage gain is reduced
– Intercarrier system
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Black-and-White Television
Receivers (Cont.)
• Video detector, or demodulator, stage
– Same detection process as radio
– Video signal is separated and fed to next
stage
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Black-and-White Television
Receivers (Cont.)
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Video amplifiers
Sound IF amplifiers
FM audio detectors
AF amplifiers
Sync separators
Sync amplifiers
Horizontal AFCs
Horizontal oscillators
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• Horizontal outputs
• Horizontal output
transformers (HOTs)
• High voltage rectifiers
• Dampers
• Vertical oscillators
• Vertical outputs
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Special-Purpose Circuits
• DC restoration
– Average value of video signal taken from
detector
– Used to set bias on the CRT
• AGC
– Provides fairly constant output from detector
– Varies gain of amplifiers
– Rectifies video signal to produce negative
voltage
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Color Television Receivers
• Developed in late 1940s by RCA Laboratories
• Shadow mask picture tubes
(Sylvania-GTE)
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Color Television Receivers (Cont.)
• Three colors used in color television
• Any color can be produced on the screen by
combining red, blue, and green
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Color Television Receivers (Cont.)
• Delta-type tubes
– Three electron guns in
neck assembly of
picture tube
– Shadow mask or
aperture ensures the
electron beams strike
the dots correctly
(Sylvania-GTE)
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Color Television Receivers (Cont.)
• Color line is made by mixing the electron beams
• In-line gun assemblies
• Color television can produce both color and
black-and-white pictures
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Television Channels
• FCC assigns portions
of radio frequency
spectrum for
television channels
– Very high frequency
(VHF)
– Ultra high frequency
(UHF)
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Television Channels (Cont.)
• Frequencies of at least 4 MHz are needed
to send a clear, sharp picture
• Upper sideband in commercial TV is
transmitted without attenuation
• Vestigial-sideband filter partly removes
lower sideband at transmitter
• Sound is transmitted as frequencymodulated signal at center frequency
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Review
What changes the frequency of the
oscillator slightly to provide the best
response?
Fine-tuning
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Review
What is the voltage amplifier stage that
increases sync pulses?
Sync amplifier
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Review
What are two special purpose circuits that
have been used to improve the basic
television circuit?
DC restoration and automatic gain control
(AGC)
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Review
What invention made color television
possible?
Shadow mask picture tube
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Television Innovations
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Video cassette recorders (VCRs)
Digital video recorder (DVRs)
Remote controls
Large-screen projection TVs
Satellite TVs
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VCRs
• Can record and play
back videotapes
• Most have four video
heads
• Magnetic tape with
iron oxide
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VCRs (Cont.)
• Can record
– Voice
– Video
– Speed information
– End of tape location
– Copyright
– Anticopy coding
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DVRs
• Combine computer and television
components
• Form a television receiver
• Receive television signal and can record
the program
• Hard disk drive used for recording medium
• Capable of recording and storage
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Remote Controls
• Application of infrared
light and digital
techniques
• Digital code sent out
of remote control
• Infrared sensor on TV
amplifies and
decodes signal
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Large-Screen Projection TVs
• Use special electron
gun assemblies to
project three separate
images onto a screen
• Loss of clarity of
video image
• 525 lines per frame
become distracting
• No real magnification
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Satellite TVs
• Geostationary orbit
• First communications satellite was
launched in 1962
• Amplifier increases strength of
communication signal for its broadcast
back to earth
• Carries both standard traveling wave
tubes and solid-state power amplifiers
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Communication Satellites
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Satellite Signals
• Signals made by
communication
stations on earth are
beamed up to
satellites
• Amplified by satellite
and then sent back to
earth
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Satellite Transmission
• Focal point
• Feedhorn
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Coaxial Cable
• Designed to carry high frequency signals
• Limits radio waves generated from center
core conductor to the area between the
core conductor and the shield
• The shield absorbs radio signal emanating
from core conductor as high frequency
passes through
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FAKRA SMB Connectors
• Very small connectors
• Designed for small diameter coaxial cable
or micro-coaxial cable
• Used for automotive satellite radio and
antenna connections
• Smallest connector used at this time
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Review
What part of a VCR reads information from
the recorded tape during playback?
Video head
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Review
What is combined to form a DVR?
A television signal and hard disk drive
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Review
Describe the signals sent to and from a
satellite.
The signal sent up from a studio is a
narrow signal targeting the satellite, while
the signal sent down from the satellite is a
wide signal designed to cover a large
area of the earth
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Review
What part of a satellite dish acts as a
receiver?
A feedhorn
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Improvements to Analog Television
• Analog television merged with digital
systems used by computer monitors
• Many features were added
• Greater color-depth control
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High Definition Television (HDTV)
• FCC approved of digital television
standard in 1996
• Allows for higher resolutions and wider
display screen than analog systems
• Uses digital broadcasting techniques
• More information-rich data to be
transmitted
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Broadcasting Multiple Channels
• Digital broadcasting can broadcast
multiple channels in same bandwidth
• Multicasting
• Datacasting
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HDTV Systems
• Digital camera to
record images at high
resolution
• Digital receiver to
convert received
broadcasts into image
and sound
• Display unit capable
of producing images
at HDTV resolution
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Charged Coupled Devices (CCDs)
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Digital Camera Technology
• CCD converts individual packets of
electrical charge into series of analog
signals representing level of light
amplitude at each photo sensor location
• Analog-to-digital converter (ADC)
• Once converted, digital pattern can be
stored or transmitted
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Three-CCD Systems
• Three sets of CCD sensors used for full-color
images and higher resolutions
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HDTV Picture Quality
• National Television Standards Committee
(NTSC) formed analog standards
• Advanced Television Systems Committee
(ATSC) developed digital standards
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ATSC Standards
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18 scanning formats
Progressive scanning
Frame rate
Aspect ratio
– 16:9
– 4:3
• HDTV capable of 720p and 1080i vertical
lines
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Analog Quality vs. Digital Quality
• Convert scan lines to maximum number of
pixels
– 480 × 440 pixels for analog
– 1920 × 1080 pixels for HDTV
• Moving Picture Experts Group developed
MPEG2 standard
• Sound quality improvements
• Enhanced definition television (EDTV)
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Digital Light Projection (DLP)
Television
• Developed based on
digital mirror device
(DMD)
• DMD can contain
over 1.3 million
mirrors
• DMD combined with
light source and lens
to create DLP system
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Flat-Panel Displays
• Many televisions now use flat-panel technology
instead of picture tubes
• Control individual pixels electrically
• Vertical and horizontal conductors
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Gas-Plasma Displays
• Electro-luminescence
• Consist of millions of cells between two glass
plates
• Controlled by varying pulses of current
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Liquid Crystal Display (LCD) Panels
• Most common flat-panel displays
• Two categories
– Active
– Passive
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How Color LCDs Work
• Backlight generates
light
• Polarized light
• Liquid crystal
between two filters
• Light passing through
filters depends on
amount of voltage
applied
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Passive-Matrix Display
• Grid of semitransparent conductors run to
each crystal
• Two major circuits
– Columns
– Rows
• Response time is slow because current
must travel along row and column until it
arrives at designated pixels
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Active-Matrix Display
• Provides better image
than passive-matrix
• Constant supply of
voltage to each cell
• Results in brighter
picture
• Thin film transistor
liquid crystal displays
(TFT-LCDs)
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LCD vs. CRT Displays
• LCDs are smaller and
lighter than CRTs
• LCDs require less power
to run
• LCDs generate less heat
• LCDs create more
detailed images
• LCDs produce less
electromagnetic
interference
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• LCDs do not have
industry-wide standard
• LCDs cost more for the
same size of CRT
• LCDs have difficulty
scaling images properly
without distortion
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Display Resolution
• Higher resolution
results in more
detailed images
• Images displayed at
lower resolutions lose
their sharpness
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Philips SXGA Triple-Input Display
Controllers
• Accept input from analog, digital, and parallel sources
– Analog input accepts UHF and VHF frequencies
– Digital input accepts HDTV broadcasts from cable and computer
systems
– Parallel interface accepts input from USB connections
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Standards Organizations
• Video Electronics Standards Organization
(VESA)
• Digital Flat Panel (DFP)
– Led by Compaq
• Digital Visual Interface (DVI)
– Led by Intel
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Home Theater Connector Types
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RF and F-type
Composite video
S-video
Component video
High Definition Multimedia Interface
ToskLink
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RF and F-Type Connections
• Support poorest quality of video images
• Found on older technologies
• Use standard coaxial cable
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Composite Video Cables
• Use only one cable
for video, two for
stereo sound
• Provide better signal
than RF or F-type
connections
• Provide worse signal
than S-video
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S-Video Connectors
• Four-pin or nine-pin
connectors
• Separate signals for
video signal chrominance
and luminance
• No way to misconnect
audio and video cables
• Video-in and video-out
(VIVO) configurations
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Component Video Connectors
• Better quality than
S-video
• Found on highperformance
devices
• Do not carry audio
signal
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High Definition Multimedia
Interface Connectors
• Supply video and audio
in uncompressed alldigital signal format
• Exceed HDTV standard
• Colorimetry
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ToskLink Connectors
• Limited to audio
• Support signals
between home
theater equipment
• Provide connections
for fiber optic cable
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Review
What is multicasting?
Broadcasting multiple channels within the
same bandwidth
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Review
What is datacasting?
Transmitting additional information along
with a video image
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Review
Which component does HDTV use in
place of the analog television’s vacuum
tube imaging?
Charged coupled device (CCD)
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Review
What committee’s standards have been
designed to replace the original television
and video standards in the United States?
Advanced Television Systems Committee
(ATSC)
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Review
What is the purpose of the MPEG2
standard?
To increase the amount of video data
transmitted in an HDTV system
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Review
Which flat-panel display system operates
on the principle of electro-luminescence?
Gas-plasma displays
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For Discussion
• Discuss the controls found in a television
receiver.
• Discuss various types of video display.
• Discuss the transition from analog to
digital television.
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