AN2483
Application note
Video signal standards
Introduction
As PC games, video editing, streaming movies on TV and DVD playback are becoming
more common, there is an increasing demand to display such video graphics on larger
display screens like those of TV rather than the PC monitors.
Analog switches are often used to route RGB data (Red, Gr een, Blue f o rmat) or component
or composite video data from different video sources, or to feed encoders with the video
data to different displays. The former is a multiplexing function while the latter is a demultiplexing function.
Interest in using analog switches in video signal routing applications is growing due the
rising trend of using lower pin count and the possibility of achieving cost reduction by
sharing the same video encoder/decoder or RAMDAC. This application note first describes
the video signal standards and then explains the various important parameters, which are
necessary to consider, in video signal sw itching.
May 2007 Rev 1 1/6
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Contents AN2483
Contents
1 Video signal standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Composite/CVBS Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Y/C Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Computer signal Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Component Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
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AN2483 Video signal standards
1 Video signal standards
The visual resolution of a video signal or display is the amount of detail that can be seen.
This is different from the resolution format of a signal or display. For example, in a computer
application, an XGA (seeTable 1) resolution has a format resolution of 1024 horizontal pixels
and 768 vertical pixels (lines), and is the implied visual resolution.
There are many diff erent kinds of vide o signals, which can be divided into eith er tele vision or
computer types. The format of signals varies from country to country. In the United States
and Japan, the NTSC format is used. HDTV/SDTV are the High Definition TV and Standar d
Definition TV. VGA and XGA are PC video resolutions. In Europe, the PAL format is
common. PAL stands for Phase Alternating Line. PAL is an improvement on NTSC format.
SECAM is used in France and stands for sequential coleur avec memoire (with memory).
Although all the above standards use t he same basic scanning system and represent colour
with a type of phase modulation, they differ in several ways, including specific scanning
frequencies, number of scan lines, and colour modulation techniques.
Table 1. Video signal comparison
Video format NTSC PAL HDTV/SDTV VGA XGA
Description
Vertical resolution
format (visible
lines/frame)
Horizontal
resolution format
(visible pixels/line)
Horizontal rate
(KHz)
Vertical frame
rate(Hz)
Highest frequency
(MHz)
The three basic video signal formats in order of decr easing quality are:
1. Composite or CVBS Interface(Colour , Video , Blanking, and Synchronization/also called
2. Y/C or S-video Interface, which use s two wire pairs.
3. Component Interface, which uses three wire pairs. In order of increasing quality, the
T elevision f ormat for
North America and
Japan
Approx 480 (525
total lines)
Determined by
bandwidth, ranges
from 320 to 650
15.734 15.625 33.75-45 31.5 60
29.97 25 30-60 60-80 60-80
4.2 5.5 25 15.3 40.7
T elevision format for
most of Europe and
South America
Approx 575 (625
total lines)
Determined by
bandwidth, ranges
from 320 to 720
High definition TV
/standard definition
TV
1080 or 720 or 480;
18 different formats
1920 or 704 or 640;
18 different formats
Composite Video Baseband Signal), which uses one wire pair.
composite (or CVBS) which uses one wire pair;
PC video
resolutions
480 768
640 1024
PC video
resolutions
In order of increasing quality, the composite (or CVBS) which uses one wire pair; Y/C (or
Svideo), which uses 2 wire pairs; and component, which uses 3 wire pairs are the 3 basic
video signal formats. Each wire pair consists of a signal and ground. The three Interfaces
differ in the level of information they can combine (encode). More encoding typically
degrades the quality but allows the signal to be carried on fewer wires. Component has the
least amount of encoding, whilst composite ha s th e mo st.
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Video signal standards AN2483
1.1 Composite/CVBS Interface
Composite video signals, which are also referred to as CVBS, are the most commonly used
analog video Interface. They combine brightness information (luma), colour information
(chroma), and synchronizing signals on just one cable. The connector is typically an RCA
jack.
Note: brightness information in the signal is the instantane ous amplitude at any point in time. The
amplitude of the modulation is proportional to the amount of colour.
1.2 Y/C Interface
Y/C signals, which are often referred to as 'S-video' signals are less encoded than those of
Composite signals. The Y signal represents brightness and the C signal represents color. .
They are both carried over 2 separate wire pairs.
1.3 Computer signal Interfaces
Virtually all computer Interfaces use RGB format signals. Picture information is carried
separately by the three base compone nts Red, Green and Blue. Synchronizing information
is typically carried as separate horizontal (H) and vertical (V) signals. The five signals, R, G,
B, H and V, are carried on one cable consisting of a shielded bundle of wires. Sometimes
the H and V synchronizes information is merged with one of the RGB signals, typically the
Green component, but this is becoming less common. This is referred to as "sync-onGreen". In rarer cases, the sync information is on the Red or the Blue signal.
1.4 Component Interface
The component signal Interf ace is t he best per former as it contains the least encoding. The
signals exist in a nearly native format. They use three pairs of wires that typically include a
luma (Y) and two color-diff er ence format signals on an RGB format signal. Color-diff eren ce
formats are normally used in TV applications, whereas an RGB format is almost always
used in computer applications. In addition to the brightness, the Y signal also contains
synchronizing information. The color-difference signals contain R (Red) minus the Y signal
and B (Blue) minus the Y signal. The theory behind this combination is that each of the
basic R, G and B components can be derived from the color-difference signals. Common
variations of color-difference signals include:
● Y, B-Y, R-Y: Luma and colour-difference signals
● Y, Pr, Pb: Pr and Pb are scaled versions of B-Y and R-Y. Commonly found in high end
consumer equipment.
● Y, Cr, Cb: Digital-signal equivalent to Y, Pr and Pb.
● Y, U, V: Not an Interface standa rd. These are intermediate, quadrature signals used in
the formation of composite and Y/C signals . Sometimes , the y are incorrectly re f erred to
as "component Interface".
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AN2483 Revision history
2 Revision history
Table 2. Revision history
Date Revision Changes
15-May-2007 1 Initial release
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AN2483
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