VGA Connector
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Video Graphics Array Video Graphics Array (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the PC industry within three years. The term can now ...
(VGA) connector is a standard connector used for computer video output. Originating with the 1987
IBM PS/2 The Personal System/2 or PS/2 is IBM's second generation of personal computers. Released in 1987, it officially replaced the IBM PC, XT, AT, and PC Convertible in IBM's lineup. Many of the PS/2's innovations, such as the 16550 UART (serial p ...
and its VGA graphics system, the 15-pin connector went on to become ubiquitous on PCs, as well as many monitors, projectors and
high-definition television High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the g ...
sets. Other connectors have been used to carry VGA-compatible signals, such as
mini-VGA Mini-VGA connectors are a non-standard, proprietary alternative used on some laptops and other systems in place of the standard VGA connector, although most laptops use a standard VGA connector. Apple, HP and Asus have separate implementations us ...
or BNC, but "''VGA connector''" typically refers to this design. Devices continue to be manufactured with VGA connectors, although newer digital interfaces such as
DVI Digital Visual Interface (DVI) is a video display interface developed by the Digital Display Working Group (DDWG). The digital interface is used to connect a video source, such as a video display controller, to a display device, such as a comp ...
,
HDMI High-Definition Multimedia Interface (HDMI) is a proprietary audio/video interface for transmitting uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controller, ...
and
DisplayPort DisplayPort (DP) is a digital display interface developed by a consortium of PC and chip manufacturers and standardized by the Video Electronics Standards Association (VESA). It is primarily used to connect a video source to a display device su ...
are increasingly displacing VGA, and many modern computers and other devices do not include it.


Physical design

The VGA connector is a three-row, 15-pin
D-subminiature The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems. Description, n ...
connector referred to variously as DE-15, HD-15 or DB-15. DE-15 is the most accurate common nomenclature under the D-sub specifications: an "E" size D-sub connector, with 15 pins in three rows.


Electrical design

All VGA connectors carry
analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analog ...
RGBHV Component video is an analog video signal that has been split into two or more component channels. In popular use, it refers to a type of component analog video (CAV) information that is transmitted or stored as three separate signals. Compon ...
(red, green, blue,
horizontal sync Horizontal scan rate, or horizontal frequency, usually expressed in kilohertz, is the number of times per second that a raster-scan video system transmits or displays a complete horizontal line, as opposed to vertical scan rate, the number of times ...
,
vertical sync Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog s ...
) video signals. Modern connectors also include
VESA VESA (), formally known as Video Electronics Standards Association, is an American technical standards organization for computer display standards. The organization was incorporated in California in July 1989To retrieve the information, searc ...
DDC pins, for identifying attached display devices. In both its modern and original variants, VGA utilizes multiple scan rates, so attached devices such as monitors are
multisync A multiple-sync (multisync) monitor, also known as a multiscan or multimode monitor, is a raster-scan analog video monitor that can properly synchronise with multiple horizontal and vertical scan rates. In contrast, fixed frequency monitors can o ...
by necessity. The VGA interface includes no affordances for
hot swapping Hot swapping is the replacement or addition of components to a computer system without stopping, shutting down, or rebooting the system; hot plugging describes the addition of components only. Components which have such functionality are said ...
, the ability to connect or disconnect the output device during operation, although in practice this can be done and usually does not cause damage to the hardware or other problems. The VESA DDC specification does however include a standard for hot-swapping.


PS/2 signaling

In the original IBM VGA implementation, refresh rates were limited to two vertical (60 and 70 Hz) and three horizontal frequencies, all of which were communicated to the monitor using combinations of different polarity H and V sync signals. Some pins on the connector were also different: pin 9 was keyed by plugging the female connector hole, and four pins carried the monitor ID. With the implementation of the VESA DDC specification, several of the monitor ID pins were reassigned for use by DDC signaling, and the key pin was replaced with a +5 V DC output per the DDC spec. Devices that comply with the DDC host system standard provide , from 50mA to 1A.


PS/55 signaling

The IBM PS/55 Display Adapter redefined pin 9 as "+12V", which signals the monitor to turn on when the system unit is powered on.


EDID

In order to advertise display capabilities
VESA VESA (), formally known as Video Electronics Standards Association, is an American technical standards organization for computer display standards. The organization was incorporated in California in July 1989To retrieve the information, searc ...
has introduced a scheme to redefining VGA connector pins 9, 12, and 15 as a serial bus for a
Display Data Channel The Display Data Channel, or DDC, is a collection of protocols for digital communication between a computer display and a graphics adapter that enable the display to communicate its supported display modes to the adapter and that enable the com ...
(DDC).


Cable quality

The same VGA cable can be used with a variety of supported VGA resolutions, ranging from 320×400px @70 Hz, or 320×480px @60 Hz (12.6 MHz of
signal bandwidth Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. It is typically measured in hertz, and depending on context, may specifically refer to ''passband bandwidth'' or ''baseband bandwidth''. ...
) to 1280×1024px (
SXGA The graphics display resolution is the width and height dimension of an electronic visual display device, measured in pixels. This information is used for electronic devices such as a computer monitor. Certain combinations of width and height a ...
) @85 Hz (160 MHz) and up to 2048×1536px (
QXGA The graphics display resolution is the width and height dimension of an electronic visual display device, measured in pixels. This information is used for electronic devices such as a computer monitor. Certain combinations of width and height ar ...
) @85 Hz (388 MHz). There are no standards defining the quality required for each resolution, but higher-quality cables typically contain coaxial wiring and insulation that make them thicker. While shorter VGA cables are less likely to introduce significant signal degradation, good-quality cable should not suffer from signal
crosstalk In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, induc ...
(whereby signals in one wire induce unwanted currents in adjacent wires) even at greater lengths. Ghosting occurs when impedance mismatches cause signals to be reflected. A correctly impedance matched cable (75ohm) should prevent this, however, ghosting with long cables may be caused by equipment with incorrect signal termination or by passive cable splitters rather than the cables themselves.


Alternative connectors

Someone high-end monitors and video cards use multiple
BNC connector The BNC connector (initialism of "Bayonet Neill–Concelman") is a miniature quick connect/disconnect radio frequency connector used for coaxial cable. It is designed to maintain the same characteristic impedance of the cable, with 50 ohm and ...
s instead of a single standard VGA connector, providing a higher quality connection with less crosstalk by utilizing five separate 75ohm
coaxial cable Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
s. Within a 15-pin connector, the red, green, and blue signals (pins 1, 2, 3) cannot be shielded from each other, so crosstalk is possible within the 15-pin interconnect. BNC prevents crosstalk by maintaining full coaxial shielding through the circular connectors, but the connectors are very large and bulky. The requirement to press and turn the plug shell to disconnect requires access space around each connector to allow grasping of each BNC plug shell. Supplementary signals such as DDC are typically not supported with BNC. Some laptops and other portable devices use a two-row mini-VGA connector that is much smaller than the three-row DE-15 connector, as well as five separate BNC connectors.


Adapters

Various adapters can be purchased to convert VGA to other connector types. One common variety is a
DVI Digital Visual Interface (DVI) is a video display interface developed by the Digital Display Working Group (DDWG). The digital interface is used to connect a video source, such as a video display controller, to a display device, such as a comp ...
to VGA adapter, which is possible because many DVI interfaces also carry VGA-compatible analog signals. Adapting from HDMI to VGA directly is not possible because HDMI includes no analog signal. For conversions to and from digital formats like HDMI or DVI-D, a scan converter is required. VGA outputs to interfaces with different signaling, more complex converters may be used. Most of them need an external power source to operate and are inherently
lossy In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...
. However, many modern displays are still made with multiple inputs including VGA, in which case adapters are not necessary. VGA can also be adapted to
SCART SCART (also known as or , especially in France, 21-pin EuroSCART in marketing by Sharp in Asia, Euroconector in Spain, EuroAV or EXT, or EIA Multiport in the United States, as an EIA interface) is a French-originated standard and associated 21- ...
in some cases, because the signals are electrically compatible if the correct sync rates are set by the host PC. Many modern graphics adapters can modify their signal in software, including refresh rate, sync length, polarity and number of blank lines. Particular issues include interlace support and the use of the resolution 720×576 in PAL countries. Under these restrictive conditions, a simple circuit to combine the VGA separate synchronization signals into SCART composite sync may suffice.


Extenders

A VGA extender is an electronic device that increases the signal strength from a
VGA port The Video Graphics Array (VGA) connector is a standard connector used for computer video output. Originating with the 1987 IBM PS/2 and its VGA graphics system, the 15-pin connector went on to become ubiquitous on PCs, as well as many monitor ...
, most often from a computer. They are often used in schools, businesses, and homes when multiple monitors are being run off one VGA port, or if the cable between the monitor and the computer will be excessively long (often pictures appear blurry or have minor artifacts if the cable runs too far without an extender). VGA extenders are sometimes called VGA boosters.


See also

*
Component video Component video is an analog video signal that has been split into two or more component channels. In popular use, it refers to a type of component analog video (CAV) information that is transmitted or stored as three separate signals. Compon ...
*
Extended display identification data Extended Display Identification Data (EDID) and Enhanced EDID (E-EDID) are metadata formats for display devices to describe their capabilities to a video source (e.g. graphics card or set-top box). The data format is defined by a standard published ...
(EDID) *
List of video connectors This is a list of physical RF and video connectors and related video signal standards. By signal standard Physical connectors D-subminiature family DVI-related DIN/Mini-DIN connector, Mini-DIN Others See also *Computer display stan ...
*
Super Video Graphics Array Super VGA (SVGA) is a broad term that covers a wide range of computer display standards that extended IBM's VGA specification. When used as shorthand for a resolution, as VGA and XGA often are, SVGA refers to a resolution of 800×600. History I ...
(SVGA)


References


External links


DE-9 pinout

DE-15 VGA VESA DDC pinout


{{AVconn Analog video connectors Computer connectors Analog display connectors