There are a variety of connection types that are used to connect display devices to computer systems, although the majority that we are likely to come across are one of the following three types:
Video Graphics Array (VGA) is possibly the longest standing and most commonly seen display device connector. It’s implemented with a 15 pin DB-15 high density connector that contains 3 rows of 5 pins. This type of connection is found on a great many computer systems, monitor devices and high definition television units. In some instances, this type of connector may also be called a HD15 or DE15 connector. On laptop computers and other small devices, a smaller ‘mini-VGA’ port is sometimes used instead of the normal, full size VGA connector.
- Analogue or Digital: Analogue
- Distance Limitations: 30 Metres for low resolution and 5 Metres for high resolution
- Frequencies: Needs a frequency of at least 6o Hz (which refreshes the screen 60 times a second, making the images appear constant to the naked eye). In order for a full frame of pixels to fit 1/60th of a second, the speed at which each is transmitted needs to be adjusted. This speed is known as the Pixel Clock.
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| A computer VGA Port |
High Definition Multimedia Interface (HDMI) is an audio/video interface for transferring uncompressed video data and compressed or uncompressed digital audio data from a display controller to a compatible peripheral device. Such devices include display monitors, video projectors, digital televisions or digital audio devices. A HDMI connector is made up of 19 pins and can support a multitude of modes such as; High Definition TV (HDTV), Standard Definition TV (SDTV) and Enhanced Digital TV (EDTV). HDMI cables can run for up to 50 feet in length and the interface has largely superseded DVI.
- Analogue or Digital: Digital
- Distance Limitations: 5 Metres
- Frequencies: HDMI 2.0 (2013) supports resolutions of up to 4K (which is 4 times the clarity of 1080p) and up to 1356 kHz audio sampling frequency. HDMI 2.0 also increased bandwidth to 18 Gbps.
- HDMI Connectors:
- Type A: 19-pin connector support all high definition (HD) modes and is electrically compatible with DVI-D Connectors.
- Type B: 29 pin connector with double video bandwidth of the Type A connector to support very high resolutions (Not yet seen in any products and possibly superseded by Display Port (See below))
- Type C: Mini HDMI connector which is used in portable devices
- Type D: Micro HDMI which is the smallest version of HDMI connector and also used in portable devices.
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| Types of HDMI connection |
Digital Video Interface (DVI) is able to transfer both analogue and digital video signals. It’s common to find this connection type on many computer systems, DVD players, high-definition televisions and home theater systems.
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| A DVI-D Cable |
- Anaglogue or Digital: Dependent on the connector type (see below)
- Distance limitations: 15 metres for low resolutions and 5 metres for high resolutions
- Frequencies: In single-link mode the maximum pixel clock frequency is 165 MHz. This supports a maximum resolution of 2.75 megapixels at a 60 Hz refresh.
- DVI Connectors:
- DVI-A: Analogue-only connection that requires a DVI-A supported interface and does not support dual link technology. DVI-A is commonly used to connect VGA devices to a DVI-A port using a VGA/DVI-A adapter.
- DVI-D: Standing for ‘DVI-digital’ is a Digital-only connection. For a single link DVI-D, the connector has 18 pins, arranged in two groups of 9 pins each. To the side of the two groups of pins is another single flat pin, known as a ‘ground bar’. This cable type is used with DVI-to-HDMI adapters. A dual link DVI-D connector contains 24 pins, arranged into three horzontal rows of 8 pins. As with the single DVI connector, it has a flat ‘ground bar’ located off to the side.
- DVI-I: Also known as ‘DVI-integrated’ it’s capable of both analogue and digital connections. In addition to the connections available on a DVI-D connector, the DVI-I connector has an additional 4 pins to carry any analogue signal. In the case of single-link connections, the connector retains the 18 pin setup in the style of the DVI-D with 4 additional pins for the analogue signal.
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| The different DVI connectors |
Other Video Interfaces
DisplayPort is a royalty-free digital display standard that aims to replace the DVI and VGA standards. Unfortunately, DisplayPort is not backwards compatible with DVI or HDMI but, by using special dual-mode ports and adapters it may still be possible to use DVI and HDMI.
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| A DisplayPort connector |
Similar to DVI and HDMI, DisplayPort uses TMDS link technology and it’s cables have 2-pin connectors. Additionally, and in a similar vein to Peripheral Component Instrument Express (PCIe), DisplayPort is also able to support high-quality gaming or other applications that require high-end graphics.
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| A SlimPort (brand of Analogix) HDMI to DisplayPort adapter which complies with the Mobility DisplayPort (or MyDP) standard |
Component video is an analogue video format that separates colour video signals into three or more channels. Ordinarily, the three channel wires are identified as Y, Pb and Pr. Y consists only of luminance and represents the brightness of the image. Whereas Pr and Pb consist of red and blue, respectively, minus the luminance. Sometimes component video can also refer to RGB signals and the three wire analogue RGB cable can often be used for high-end video cameras.
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| Component video cables |
Composite video is simply an analogue video format that combines all of the video information into a single channel. Composite video attempts to combine the information contained on analogue Component video channels and, consequently, does not provide a high level of quality. As technology continues to progress, composite video ports are becoming much rarer on devices.
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| A composite video cable and jack. |
Radio Corporation of America (RCA) cables carry audio and video transmissions to a wide variety of different devices such as; televisions, digital cameras and gaming consoled. RCA cables can also be used to carry digital audio, to send audio to loud speakers or even as a power cable. RCA cable male connectors, and their female opposites on devices, are colour coded so as to provide a guide for users to know which cables to connect. The most common RCA colours are; Yellow, for a variety of composite connections; Red, for the right audio channel connection and; White, for the left audio channel connection.
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| An example of RCA cables |
Coaxial cable, also abbreviated to ‘coax’, is a cable that features a conducting central copper core, which is surrounded by an insulator and braided or foil shielding. The included insulator keeps the copper core and the shield separate and the entire package is wrapped in another insulating layer, known as a ‘jacket’. The data information is transmitted through the central conductor, while the outer shielding functions to reduce electromagnetic interference.
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| Coaxial cable and it’s parts: A – The outer jacket. B – The shield. C – The insulating layer. D – The central copper core |
Bayonet Neill-Concelman (BNC) connectors are used with coaxial cable in order to carry radio signals to and from devices. BNC cables are commonly used to connect radio equipment and avionic components, although they are also able to carry video signals if required. The actual BNC connections themselves come in two different versions.the 50 Ω and the 75 Ω.
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| The two different types of BNC connectors, showing both male and female versions. |
MiniDIN-4 connectors are used with S-Video connections. S-Video is a type of analogue video signal that carries video data as separate, brightness and colour, signals. S-Video works in only two resolutions, 480i or 576i, and older versions of the system from the 1980s used different sized DIN connectors for various connections.
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| A miniDIN-4 S-Video connector |
Video Adapters and Converters
Computers with built-in video cards and the associated monitors need to have a common connector type in order for them to connect and operate correctly. Not every monitor has every type of connector and nor does every computer have every type of connector port. It is possible to buy video graphics cards and add them to a computer system in order for it to be able to connect to a given display device, but it may be possible to achieve the same result more more cheaply by using a converter or adapter.
Adapters and converters can come in a variety of different styles, some simply a plastic housing with the different connectors at each end and others connected by a cable. Some of the more commonly found adapters include:
- DVI to HDMI
- DVI to VGA
- Thunderbolt to DVI
- HDMI to VGA
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