An Overview of Current Display Interfaces

4
VGA
The VGA connector – named for the Video Graphics Array standard introduced by
IBM for the original Personal Computer products in 1987, has been the most
successful PC monitor interface to date in the computer industry.
In use now for almost 25 years, the VGA (also known as the 15HD connector,
for15-pin high-density D-subminiature) remains the standard analog video interface
of the PC industry, but is beginning to experience limitations. The D-subminiature
connector family from which this connector was originally selected was never
intended to handle very-high-frequency video, and VGA connections can often
show the effects of low bandwidth, overall signal loss, and “ghosting” from
impedance mismatches in the system. The use of cable extenders and switches often
introduces additional problems of this nature. The popularity of the VGA connector
continues primarily because it is inexpensive and has an enormous installed base –
and the latter is not a minor concern as the industry tries to transition to newer,
more capable interfaces. The analog section of the DVI-I standard carries VGA-
compatible video, can interoperate with this standard, and will typically provide far
better video performance, particularly for video timings and formats over 1280 x
1024 resolution. However, fully-digital interfaces to the DisplayPort interface in PC
applications and HDMI for TV/CE products) are the long-term solutions. Analog
interfaces in general, and VGA in particular, are expected to decline in popularity
over the next few years, especially as the industry faces the “analog sunset”
requirements for the use of content-protected material (such as DVDs and Blu-ray
discs).
Figure 1. VGA Connector
Table 1. VGA Connector Pinout
Pin
Signal
Pin)
Signal
1
Red video
9
+5 VDC
2
Green video
10
Sync return
3
Blue video
11
unused
4
unused (nc)
12
DDC Data (SDA)
5
Return
13
Horizontal sync
6
Red return
14
Vertical sync
7
Green return
15
DDC clock (SCL)
8
Blue return
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Note: This pinout refers to the VESA DDC (Display Data Channel) version of the VGA
connector, which is currently the most widely used. It is identified by the blue color of the
center part of the receptacle.