Video and monitor terms
I have collected here descriptions of vidoe terms related to
computer video technology and monitors.
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- BNC: A connector used for connecting coaxial cables to monitor.
- Cathode Ray Tube: The picture tube type used in normal computer monitors.
- Characteristic impedance: The characteristic impedance
describe the high frequency characteristics of the coaxial cable.
The coaxial cables used with computer monitors and video systen
have a characteristic impedance of 75 ohms, which means that those
cables look like 75 ohm load to the high frequency signal and the
system works best when the both ends of the cable are terminated with
75 ohm resisotrs. Radio engineers usually use 50 ohm coaxial cables
and you should not mix up those two different cable types.
- Coaxial cable: A cable which has one center conductor,
insulation around it and an outer conductor as a shield around
the center conductor and it's insulator. This type cable is
used to carry high frequency electrical signals like radio
waves and high frequency video signals. The coaxial cables used
with computer monitors have a characteristic impedance of 75 ohms.
- Composite Sync: The horizontal and vertical
sync signals are combined into one signal. In this configuration, monitors with
BNC connections use four connections: red,
green, blue, and sync.
- CRT: Short for Cathode Ray Tube.
- ECL: Short for Emitter-Coupled Logic.
This type of high speed logic signals are mostly found in super
high resolution CAD/CAM computer monocrome displays (for example
- External Sync: This term means that the sync signals are
sent to the monitors "externally", separated from the RGB
video signals. This means that there is a separate connector
or connectors besides the RGB connectors for the sync signals.
Separate horizontal and vertical syncs and Composite Sync belong
to this category.
- Fixed Frequency Monitor: A computer monitor which is
designed to operate at only one screen resolutions with strictly
fixed horizonal and vertical sync frequencies.
- Horizontal Back Porch: The period of time between the end of the
Horizontal Sync pulse and the start of the next
horizontal active time is the Horizontal Back
- Horizontal Blank Time: Once the beam has reached the right side of
the screen it is quickly moved back to the left
side of the screen. As the beam is being
directed back, it is always turned off and the
time it takes to move back is called the
horizontal blank time.
- Horizontal Front Porch: The time
between the end of the horizontal active time
and the start of the horizontal sync pulse is
called the Horizontal Front Porch.
- Horizontal Sync Width: The amount
of time that the horizontal sync pulse is active
is called the Horizontal Sync Width.
- Horizontal Total Time: The time it takes to make a full
horizonal cycle is referred to as the
horizontal total time. Adding the Horizontal
Active and Horizontal Blank times together
equals the Horizontal Total Time.
- Horizontal Refresh Rate: The number of
horizontal cycles per second is referred to as
the Horizontal Refresh Rate and is usually in
units of thousands of cycles, Kilohertz.
For example, if a monitor horizontally cycles
50,000 times a second, its Horizontal Refresh
Rate is 50.0 Kilohertz (written as 50.0 kHz).
- Horizontal Sync Pulse: During the horizontal blank time, the monitor
receives the horizontal sync pulse which is used for syncronizing the
monitor to operate exactly syncronous to the PC graphics card.
After receiving the horizontal sync pulse, the monitor
returns the beam to the left side of the screen.
- Horizontal Total Time: Time it take to make a
complete horizonal cycle.If a monitor
runs at 50 kHz horizonal refresh rate, each horizontal cycle takes
1/50,000 of second, or 20 microseconds (20
one-millionths of a second).
- Interlaced Scan: A way to refresh a monitor so that
screen is refreshed from up left corner to right bottom corner so
that every scanline is scanned in every screen refresh.
This method is used in broadcast television to save radio bandwidth,
but this is nowadays very rarey used for computer monitors because gives
slightly unstable image on computer screen.
- Interlacing: Same as Interlaced Scan.
- Internal sync: This term describes tells that the sync
signals are combined "inside" the video signal instead of sending
them separately. For RGB signals the most common "Internal Sync"
method is Sync On Green.
- Multisync Monitor: A monitor which can work
with many differenc combinations of different vertical
and horizonal sync frequencies and different screen resolutions.
- RGB: Short for "Red, Green and Blue".
Means the primary colors of the computer video system or
the video signals and/or connectors associated with them.
- Separate horizontal and vertical syncs: The
horizontal and vertical sync signals are sent as
two separate signals. In this
configuration, monitors with BNC connections
use five connections: red, green, blue,
horizontal sync, and vertical sync.
- SVGA: Short for SuperVGA. An extension to VGA standard
to make the same graphics system to support high resolutions.
- Sync On Green: The horizontal and vertical
sync signals are combined together with the
green signal. In this configuration, monitors
with BNC connections use three connections:
red, green, and blue.
- TTL: Short for Transistor-Transistor Logic. In computer
video technology this digital 4-5 Vpp signal is used for short cable runs
on old video standards like IBM CGA and EGA.
- Vertical Active Time: The total
time it takes for all of the horizontal scanlines
to be displayed is called the vertical active
- Vertical Back Porch: The period of
time between the end of the Vertical Sync pulse
and the start of the next vertical active time is
the Vertical Back Porch.
- Vertical Blank Time: The
time it takes for the beam to be returned to
the top is called the vertical blank time.
- Vertical Front Porch: The
time between the end of the vertical active time
and the start of the vertical sync pulse is called
the Vertical Front Porch.
- Vertical Refresh Rate: The Vertical Refresh Rate of a monitor is
simply the number of vertical cycles
completed per second, measured in Hertz.
For example, if a monitor completes 75
vertical cycles per second, its Vertical
Refresh Rate is 75 Hertz (75 Hz).
- Vertical Sync Pulse: During the vertical blank time, the monitor
receives the vertical sync pulse which is used for syncronizing the
monitor to operate exactly syncronous to the PC graphics card.
After receiving the vertical sync pulse, the monitor
returns the beam to the upper left corner of the screen.
- Vertical Total Time: The time it
takes for the beam to start at the top of the
screen, scan back and forth to the bottom of
the screen, and return to the top, is called the
vertical total time. Adding the Vertical
Active Time to the Vertical Blank Time will
equal the Vertical Total Time.
- Vertical Sync Width: The amount of time
that the vertical sync pulse is active is called
the Vertical Sync Width.
- VGA: A PC video standard invented by IBM.
Maximum resolution supported by original VGA satdard is 640x480.
- Vpp: Short for Volts Peak to Peak.
Tomi Engdahl <[email protected]>
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