chapter 23 television and video display units © goodheart-willcox co., inc.permission granted to...

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.

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.

Objectives

• Explain the difference between multicasting and datacasting.

• Discuss the compression technique of MPEG2.

• Discuss the various flat-panel technologies.

Television Signals

• Television cameras

• Scanning

• Composite video signals

• Basic CRT controls

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

Image Orthicons

• Varying degrees of light cause electrons to be emitted on the target side of the cathode and form an electronic image

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

Scanning (Cont.)

• 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

Scanning (Cont.)

• Deflection yoke• Synchronization (sync

) pulse• Horizontal hold• Vertical hold

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

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

Composite Video Signals (Cont.)

• Screen is driven back to the pedestal, or blanking level

• Sync pulse is sent in infrablack region for oscillator synchronization

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

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

Review

What is scanning?

The point-to-point examination of a picture

Review

How many scanning lines are used in the scanning system of the United States?

Review

What is a raster?

The lines on a TV screen when a vacant channel is showing

Television Receivers

• Black-and-white television receivers• Color television receivers• Television channels

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

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

• Video detector, or demodulator, stage– Same detection process as radio– Video signal is separated and fed to next

• Video amplifiers• Sound IF amplifiers• FM audio detectors• AF amplifiers• Sync separators• Sync amplifiers• Horizontal AFCs• Horizontal oscillators

• Horizontal outputs• Horizontal output

transformers (HOTs)• High voltage rectifiers• Dampers• Vertical oscillators• Vertical outputs

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

Color Television Receivers

• Developed in late 1940s by RCA Laboratories• Shadow mask picture tubes

(Sylvania-GTE)

Color Television Receivers (Cont.)

• Three colors used in color television• Any color can be produced on the screen by

combining red, blue, and green

• 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)

• Color line is made by mixing the electron beams • In-line gun assemblies• Color television can produce both color and

black-and-white pictures

Television Channels

• FCC assigns portions of radio frequency spectrum for television channels– Very high frequency

(VHF)– Ultra high frequency

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 frequency-modulated signal at center frequency

Review

What changes the frequency of the oscillator slightly to provide the best response?

Fine-tuning

Review

What is the voltage amplifier stage that increases sync pulses?

Sync amplifier

Review

What are two special purpose circuits that have been used to improve the basic television circuit?

DC restoration and automatic gain control (AGC)

Review

What invention made color television possible?

Shadow mask picture tube

Television Innovations

• Video cassette recorders (VCRs)

• Digital video recorder (DVRs)

• Remote controls

• Large-screen projection TVs

• Satellite TVs

• Can record and play back videotapes

• Most have four video heads

• Magnetic tape with iron oxide

VCRs (Cont.)

• Can record– Voice– Video– Speed information– End of tape location– Copyright– Anticopy coding

• 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

Remote Controls

• Application of infrared light and digital techniques

• Digital code sent out of remote control

• Infrared sensor on TV amplifies and decodes signal

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

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

Communication Satellites

Satellite Signals

• Signals made by communication stations on earth are beamed up to satellites

• Amplified by satellite and then sent back to earth

Satellite Transmission

• Focal point• Feedhorn

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

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

Review

What part of a VCR reads information from the recorded tape during playback?

Video head

Review

What is combined to form a DVR?

A television signal and hard disk drive

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

Review

What part of a satellite dish acts as a receiver?

A feedhorn

Improvements to Analog Television

• Analog television merged with digital systems used by computer monitors

• Many features were added

• Greater color-depth control

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

Broadcasting Multiple Channels

• Digital broadcasting can broadcast multiple channels in same bandwidth

• Multicasting

• Datacasting

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

Charged Coupled Devices (CCDs)

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

Three-CCD Systems

• Three sets of CCD sensors used for full-color images and higher resolutions

HDTV Picture Quality

• National Television Standards Committee (NTSC) formed analog standards

• Advanced Television Systems Committee (ATSC) developed digital standards

ATSC Standards

• 18 scanning formats• Progressive scanning• Frame rate• Aspect ratio

– 16:9– 4:3

• HDTV capable of 720p and 1080i vertical lines

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)

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

(Courtesy of Texas Instruments)

Flat-Panel Displays

• Many televisions now use flat-panel technology instead of picture tubes

• Control individual pixels electrically• Vertical and horizontal conductors

Gas-Plasma Displays

• Electro-luminescence• Consist of millions of cells between two glass

plates• Controlled by varying pulses of current

Liquid Crystal Display (LCD) Panels

• Most common flat-panel displays

• Two categories– Active– Passive

How Color LCDs Work

• Backlight generates light

• Polarized light• Liquid crystal

between two filters• Light passing through

filters depends on amount of voltage applied

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

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)

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

• LCDs do not have industry-wide standard

• LCDs cost more for the same size of CRT

• LCDs have difficulty scaling images properly without distortion

Display Resolution

• Higher resolution results in more detailed images

• Images displayed at lower resolutions lose their sharpness

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

Standards Organizations

• Video Electronics Standards Organization (VESA)

• Digital Flat Panel (DFP)– Led by Compaq

• Digital Visual Interface (DVI)– Led by Intel

Home Theater Connector Types

• RF and F-type

• Composite video

• S-video

• Component video

• High Definition Multimedia Interface

• ToskLink

RF and F-Type Connections

• Support poorest quality of video images

• Found on older technologies

• Use standard coaxial cable

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

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

Component Video Connectors

• Better quality than S-video

• Found on high-performance devices

• Do not carry audio signal

High Definition Multimedia Interface Connectors

• Supply video and audio in uncompressed all-digital signal format

• Exceed HDTV standard• Colorimetry

ToskLink Connectors

• Limited to audio• Support signals

between home theater equipment

• Provide connections for fiber optic cable

Review

What is multicasting?

Broadcasting multiple channels within the same bandwidth

Review

What is datacasting?

Transmitting additional information along with a video image

Review

Which component does HDTV use in place of the analog television’s vacuum tube imaging?

Charged coupled device (CCD)

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)

Review

What is the purpose of the MPEG2 standard?

To increase the amount of video data transmitted in an HDTV system

Review

Which flat-panel display system operates on the principle of electro-luminescence?

Gas-plasma displays

For Discussion

• Discuss the controls found in a television receiver.

• Discuss various types of video display.

• Discuss the transition from analog to digital television.

chapter 23 television and video display units © goodheart-willcox co., inc.permission granted to...

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