VGA connector
VGA connector (engl. V ideo G raphics A rray) the specification includes an analog electronic interface for the transmission of moving pictures between graphics and display devices as well as specifications for this purpose appropriate plug and cable. The introduction took place in 1987 simultaneously with the Video Graphics Array from IBM and followed the EGA connection .
The analog VGA signal is generated by the video display controller / RAMDAC of the graphics card.
With current screen technologies such as TFT displays, it is no longer necessary to convert the digital image of the graphics card into an analog signal, since a digital signal is required in the screen unit anyway. VGA has been replaced by digital connection types such as DVI , HDMI or DisplayPort , which work on a purely digital level and avoid conversion losses. Related standards exist for analog transmission of NTSC and PAL TV signals, e.g. B. RGB , S-Video and F-BAS .
In the past, the 13W3 connector type was used in workstations from Sun , Silicon Graphics and IBM , among others , with which the image signals are better shielded. The electrical signals are otherwise identical.
A more compact variant, sometimes used in laptops, is mini-VGA , which differs only mechanically and not electrically from the original VGA connection.
The PC-99 standard has prescribed the blue color for VGA plugs and sockets since 1999.
At the end of 2010, Intel and AMD announced that they would no longer support VGA in their products from 2015. In the future, the focus will be on the HDMI and DisplayPort interfaces .
Connector
A VGA connector is a 15-pin mini D-Sub connector (also called a D-Sub mini connector) with three rows of connections (type HD15).
The output of the graphics card is always a socket , the input on the display device can in principle be of both sexes (cf. eng. Male = plug, female = socket) (depending on the device model). As a rule (all modern tube and LCD monitors) this is also a socket, so that a connection cable needs two connector ends. Many display devices (monitors) also have a permanently attached cable, which ends with a plug and fits into the socket of the graphics card in the PC.
The successor to the VGA and DVI connection is the DisplayPort .
 The socket in the mating direction. |
|
|---|---|
| Pin code | function |
| 1 | Red (0.7 V pp @ 75 ohms) |
| 2 | Green (level & impedance see above) or (analog) monochrome signal |
| 3 | Blue (level & impedance see above) |
| 4th | ID2 (monitor ID identification # 2) or reserve |
| 5 | digital ground for DDC |
| 6th | analog ground for red |
| 7th | analog ground for green |
| 8th | analog ground for blue |
| 9 | not used; glgt. +5 V from the graphics card (= computer connected) |
| 10 | analog ground for sync signals |
| 11 | ID0 |
| 12 | ID1 or digit. Data exchange (DDC - SDA, S erial DA ta = data line) |
| 13 | Horizontal synchronization or common sync. (H + V) |
| 14th | Vertical synchronization |
| 15th | Digit. Data exchange ( DDC - SCL, S erial CL ock = clock line) |
The signal level is (except for the data lines) 0.7 V ps with 75 Ω impedance . Depending on the quality, VGA cables can be significantly susceptible to interference with lengths of less than 5 m, or they can still transmit a good signal when the cable is over 30 m. A cable suitable for high frequencies (low attenuation, high shielding (> 65 dB ), suitable impedance (75 Ω)) with a coaxial structure for the color channels is advantageous.
In general, the VGA connection can be used up to 400 MHz video bandwidth, which is sufficient for resolutions of up to 2560 × 1440 pixels at a frame rate of 75 Hz. At high resolutions, blurring (by rounding off the signal edges) and / or shadow images (by reflections in the analog connection) can become clearly visible, depending on the cable quality.
With flat screens and video projectors , with a VGA connection, the digital image generated by the graphics card must first be analogized with losses and then re-digitized in the display device, which leads to a loss of quality. Therefore, digital connections are preferable here.
DDC1 uses pin 14 (V-Sync) as SCL, but only a simplified data signal goes from the monitor to the PC, DDC2 uses pin 15 for this, but supports signals in both directions and has more functions.
| If a DDC signal cannot be used, the older "ID" system can also be used. |
||||
|---|---|---|---|---|
| Pin 11 | Pin 12 | Pin 4 | Explanation | |
| ID0 | ID1 | ID2 | ||
| NC | NC | NC | no monitor connected | |
| Dimensions | Monochrome monitor | |||
| Dimensions | Color monitor resolution 800 × 600 | |||
| Dimensions | Dimensions | Color monitor resolution 1024 × 768 | ||
Depending on the resolution (s) there are even more combinations (PIN 15 is then sometimes referred to as ID3)
Note : Some modern graphics cards and projectors also support an HDTV output ( component video ) on the VGA connector; then a YPbPr signal is transmitted instead of the RGB signal . The assignment is typically, but not mandatory, red difference = Pr on pin 1, gamma-corrected brightness = Y on pin 2 (with sync), blue difference = Pb on pin 3, pins 6 to 8 ground, rest NC (engl. not connected , i.e. not used).
Signal properties
Due to the generation of different pixel frequencies by the graphics card, the use of adjustable low-pass filters to limit the video bandwidth according to the RAMDAC is technically hardly feasible. A VGA signal is therefore not subject to any band limitation, which leads to a step-like course of the analog signal in the pixel cycle with possible overshoots after pixel edges. The processing of such signals is usually unproblematic with purely analog CRT monitors, but can lead to problems with LCD flat screens. For display on an LCD, the signal must first be digitized again with an analog-to-digital converter (ADC), which requires correct setting of the pixel frequency and the pixel phase (time of ADC sampling during each pixel duration). In today's flat screens, this is accomplished by automatic routines within 0.5–2 s, but does not always succeed without errors, so that manual fine-tuning may be necessary for each image resolution used.
resolution
Originally, the VGA connection was only designed for a resolution of up to 640 × 480 pixels on analog screen tubes. Up to 1280 × 720 pixels, the use of VGA is normally unproblematic, with good graphics cards and monitors even up to the Full HD range of 1920 × 1080 pixels. Due to the D / A conversion, which is more computationally intensive with many pixels, older graphics cards above 1280 × 720 pixels can possibly stall and the limited RF properties of a VGA cable can lead to contrast problems . With good VGA cables or BNC cables with VGA connection, however, even higher resolutions such as B. 2048x1536 easily possible. The limits result mainly from the maximum RAMDAC frequency of the graphics card; 400 MHz is common with newer graphics cards.
Relationship to DVI
DVI , the digital successor to VGA, also has some pins in which an analog VGA signal is transmitted. The manufacturer decides whether an analog signal is fed via these existing pins. This is indicated with the addition "I" or "A": DVI-I and DVI-A. If there is an analog signal, VGA devices can also be operated on DVI outputs with a simple adapter.
Individual evidence
- ↑ Intel and AMD seal the end of the VGA interface , golem.de, December 9, 2010, accessed on December 9, 2010.
- ↑ z. B. there is a Mitsubishi tube monitor with 2048x1536 @ 86Hz (corresponds to 390 MHz video bandwidth ).