T ELEVISION - 1 T Srinivasa Rao1Communication Systems (EC-326)
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Transcript of T ELEVISION - 1 T Srinivasa Rao1Communication Systems (EC-326)
TELEVISION - 1
T Srinivasa Rao 1Communication Systems (EC-326)
EC 326 COMMUNICATION SYSTEMSUNIT - III
T Srinivasa RaoT Srinivasa RaoDept. of ECE
Bapatla Engineering College
Part 1
Vision characteristics and scanning systems, Composite video signal.
Part 2 Camera tubes: Principle of operation, Image
Orthicon, Vidicon, Plumbicon.
Part 3Block diagram of broad cast TV transmitterBlock diagram of broadcast TV receiver.
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Elements of a T V System
Picture Transmission Sound Transmission Picture Reception Sound Reception Synchronization Receiver Controls Colour Television.
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Basic monochrome television transmitter
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Basic monochrome television receiver
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Simplified cross-sectional view of a Vidicon TV camera tube
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Path of scanning beam in covering picture area
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Elements of a picture tube
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Signal transmission paths illustrating compatibility between colourand monochrome TV systems.R, G and B represent three camera tubes which develop video signals corresponding to the red, green and blue contents of the scene being televised
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Television System
NTSC Standard(National Television Standards Committee)
• Standard for U.S., Japan, and Korea• 4 X 3 Aspect Ratio• 525 Lines• 30 Frames Per Second• Scanned in "Fields"
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PAL System(Phase Alternating Line)
• Another World Television Standard • 4 X 3 Aspect Ratio• 625 Lines• 25 Frames Per Second• Scanned in "Fields"• There are Slight Variations: PAL-B, -G, -H, -N • Used in Continental Europe and Parts of Africa,
Middle East & So. America• More Lines = Better Resolution• Fewer Frames/Fields = More "Flicker"
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SECAM System (Sequential Color and Memory) • Another World Television Standard • 4 X 3 Aspect Ratio• 625 Lines• 25 Frames Per Second• Scanned in "Fields“• Used in France, Eastern Europe and Parts of the
Middle East & Africa• More Lines = Better Resolution• Fewer Frames/Fields = More "Flicker"
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HDTV System (High Definition Television)
• 16 X 9 Aspect Ratio• A Digital System• Permits Several Levels of Picture Resolution Similar to that of
High-Quality Computer Monitors, With 720 or 1080 Lines (1280 x 720 pixels or 1920 x 1080 pixels)
• Ranges from 24 to 60 frames per second, progressive or interlaced scan
• Uses MPEG-2 Compression to squeeze a 19 megabit-per-second data flow so that it can be accommodated by a standard broadcast TV channel of 6 MHz bandwidth
• 5.1 Channels of Dolby AC-3 Digital Surround-Sound Audio T Srinivasa Rao 14Communication Systems (EC-326)
Vidicon TV Pick-up Tube
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Communication Systems (EC-326)
Basic Factors
Structure ( Aspect ratio – 4:3 ) Continuity ( 25 FPS ) Scanning lines (860 x 0.7) Flicker ( Interlaced Scanning) Resolution ( Vertical & Horizontal) Other factors.
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Television Scanning• beam scanning for standard TV– 625 lines in total image– 25 images (framesframes) scanned per second
• Oscillators– Vertical– Horizontal
Vertical(Slower)
Horizontal(Faster)
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CRT
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TV Interlacing• frameframe scanned in two passes, first the odd
lines then the even– One frame takes 1/25th second– avoids flicker
• each pass called a fieldfield– takes 1/50th second
1st Field (Odd lines) 2nd Field (Even lines)
+ =
+ = One Frame
1/50th sec. 1/50th sec. 1/25th sec.T Srinivasa Rao 19Communication Systems (EC-326)
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Synchronization• TV Camera & Monitor must be
synchronized– beam at same place on image
• special sync pulses sent at end of each horizontal line & vertical field
• retrace– horizontal retrace• beam returned to left side of screen
– vertical retrace• beam returned to the top of screen
– Turns off video during retrace
Vertical Retrace
Horizontal Retrace
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Image Formation and Display
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Video Signal
• Voltage level indicates brightness• Blanking during non-video
– retrace
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Vertical Resolution
• proportional to # of vertical scan lines
• theoretic maximum– half # of visible scan lines– black lines alternate with white• max. line pairs = video lines / 2
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Details of Horizontal Scanning
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Characteristics of the 625-B Monochrome TV System
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Next…
Television – 2
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