Monday, July 1, 2013
Executive
Summary
Most of the computers on the market today
generate digital video, which is then converted to analog by the video graphics
card and transmitted to an analog CRT monitor. In the case of digital displays
such as Plasma, LCD flat panel monitors, DLP and LCD projectors, that analog
signal is then converted back to digital before it can be displayed, a process
that can add unnecessary cost and complexity to some products. Additionally the
digital to analog (D/A) and analog to digital (A/D) conversion of the video
signal can introduce sampling errors, which can reduce image quality and
require the addition of controls to help correct the errors introduced in the
process.
With the increase in popularity of digital
flat panel monitors, the need for a digital graphics connection became
apparent. The challenge was to develop a simple, cost effective digital
connection to send high bandwidth digital RGB signals across a reasonable cable
length. Solutions based on National Semiconductor’s Low Voltage Differential
Signaling (LVDS) technology and Silicon Image’s Transition Minimized
Differential Signaling (TMDS) technology were explored. TMDS proved to be
better suited to transmit digital signals across long cable lengths than LVDS
technology. A number of competing standards for digital interfacing soon
emerged. VESA introduced the Plug and Display (P&D) standard, Compaq
Corporation led a consortium of manufacturers to introduce the Digital Flat
Panel (DFP) interface standard and the Digital Display Working Group (DDWG)
introduced the Digital Visual Interface (DVI) standard. All three standards
were based around Silicon Image’s TMDS technology.
The Plug and Display (P&D) standard
attempted to implement a multifunction interface with support for USB and IEEE1394/Firewire.
It failed to attract the interest of video graphics card manufacturers and
never gained much popularity. The Digital Flat Panel (DFP) standard was
introduced as a way to simplify the implementation of an all-digital
connection. It failed to gain widespread acceptance because of its limited
functionality. The Digital Visual Interface (DVI) was designed to provide the
industry with a single, universal digital interface. Its primary focus was to
provide a digital connection between a PC and a display device. It quickly
gained widespread market acceptance and is now the industry standard.
DVI offers the right combination of
versatility and functionality, which is why it has become the industry
standard. Market research indicates that in just a few years, sales of digital
display devices will surpass sales of analog display devices. DVI is poised to
replace the analog VGA connector to become the single, universal display
interface.
Direct
Digital Transmission Standards
Low Voltage Differential Signaling (LVDS)
National Semiconductor’s Low Voltage
Differential Signaling (LVDS) is a high-speed, low-power interface used by most
Notebook computer manufacturers to create a direct digital connection between
the Central Processing Unit (CPU) and LCD display. It provides very high line
transmission rates, requires little power, generates low noise levels and it is
very robust. It is also able to reject common-mode noise that is twice the
magnitude of the actual differential signal magnitude. LVDS technology was
optimized for short cable runs, as a result efforts to transition LVDS
technology to external desktop monitors did not get too far.
Transition Minimized Differential Signaling
(TMDS)
Silicon Image’s Transition Minimized Differential
Signaling is an electrical standard used to transmit digital data to a display
device. The transition minimization is achieved by implementing an advanced
encoding algorithm that converts 8 bits of data into a 10-bit transition
minimized, DC balanced character. The signal is optimized to reduce
Electromagnetic Interference (EMI), which allows for faster signal transfer
rates with increased accuracy. The differential circuitry in TMDS allows
complimentary limited amplitude signals to be transmitted over twisted pair
wires instead of more expensive coaxial cable. The TMDS link architecture
consists of a TMDS transmitter that encodes and serially transmits a data
stream over the TMDS link to a TMDS receiver. Video and sync information are
serialized and sent over three sets of twisted pair wires, one set for red,
green and blue data channels. An additional pair of wires is used to transmit a
clock signal for timing. At the other end, the TMDS receiver synchronizes
itself to character boundaries in each of the serial data streams, the
transmitted signal is recovered and decoded.
A fundamental principle of physics known as
the "Copper Barrier" limits the amount of data that can be squeezed
through a single copper wire. The limit is a bandwidth of about 165MHz, which
equates to 165 million pixels per second. A single TMDS link has a bandwidth of
165 MHz, which enough to display resolutions of up to 1600 x 1200 (UXGA) at
60Hz.
DVI, which is the first standard
specifically written for the TMDS digital interface allows for up to two TMDS
links, a total of 6 channels sharing a single clock, to be integrated into a
single DVI connector to support a minimum bandwidth of 330 mega pixels per
second. That is enough bandwidth to enable digital
displays to reach resolutions of up to 2048 x 1536 (QXGA).
TMDS
Based Transmission Standards
Plug-and-Display (P&D)
The P&D standard attempted to implement
a multifunction connector capable of carrying digital and analog signals, as
well as USB and IEEE1394/Firewire. Although the P&D connector failed to
attract the interest of graphics card manufacturers, InFocus Corporation, one
of the leaders of the projection industry, has found a great application for
this connector in its products. By using the P&D connector, which InFocus
calls the M1-DA, on the display side, InFocus has created an organized,
single-cable connection solution between the host computer and the display. In
recognition of this, VESA has officially released the M1 standard, making this
the first time that a projector manufacturer has played such a pivotal role in
the creation of a connector standard.
Digital Flat Panel (DFP)
Adopted by VESA and now considered obsolete,
the DFP standard was designed to simplify the implementation of a direct
digital connection between the host computer and a digital flat panel monitor.
DFP supports the Display Data Channel (DDC) and Extended Display Identification
Data (EDID) specifications for configuration management. It also supports Hot
Plug Detection for compatibility with the P&D VESA standard. It does not
support the transmission of analog signals and it does not support USB or
IEEE1394/Firewire. Its maximum resolution is limited to SXGA (1280 x 1024),
which made it the least future-ready of the three standards.
Digital Visual Interface (DVI)
The Digital Visual Interface (DVI) was
designed to provide the industry with a single, universal digital interface.
Its primary focus was to provide a digital connection between a PC and a
display device. The DVI interface has proven to be extremely versatile. Its two
connector styles provide manufacturers with the flexibility to support digital
devices while remaining backwards compatible with analog devices. DVI is also
backwards compatible with the Plug and Display (P&D) and Digital Flat Panel
(DFP) standards through the use of adapters. Since its release, DVI has gained
extra functionality and can now be used to deliver secure content to a display
device as well as deliver the highest quality digital audio signals. The DVI
interface has gained industry wide acceptance and is considered the industry
standard digital graphics interface. The projection industry has embraced DVI
in a big way. Making the DVI connector a standard feature on the majority of
new projector models on the market.
The
Digital Visual Interface (DVI)
The DVI standard was introduced
by the Digital Display Working Group (DDWG) to create a universally accepted
digital interface and to provide the industry with a path towards a single
common display interface. DVI is based on Silicon Image’s Transition Minimized
Differential Signaling (TMDS) technology, which provides a high-bandwidth
digital connection between the host computer and a display device. The TMDS
technology also makes DVI backwards compatible with the Plug and Display
(P&D) and Digital Flat Panel (DFP) standards through the use of adapters.
DVI is the first digital
standard specifically created for Transition Minimized Differential Signaling,
It supports a dual-link mode, which allows digital displays to reach
resolutions up to 2048 X 1536 (QXGA) and beyond.
The DVI specification supports hot plug and
play of display devices. DVI also supports the VESA Display Data Channel (DDC)
and Extended Display Identification Data (EDID) specifications, which enable
the display, graphics adapter, and computer to communicate and automatically
configure the system to support the different features available in the
display. EDID is a standard data format for information such as display vendor,
resolution and timing capabilities. A purely digital
connection allows projector manufacturers to design products, which provide the
sharpest, clearest image possible, without the need for any fine sync or
complex pixel clock adjustments.
|
DISPLAY RESOLUTION CHART
|
|
|
Resolution
Name
|
Pixel Resolution
|
|
Video
Graphics Array (VGA)
|
640 x 480
|
|
Super
VGA (SVGA)
|
800 x 600
|
|
Extended
Graphics Array (XGA)
|
1024 x 768
|
|
Super
XGA
|
1280 x 1024
|
|
Ultra
XGA
|
1600 x 1200
|
|
High
Definition TV (HDTV)
|
1920 x 1080
|
|
Quad
XGA (QXGA)
|
2048 x 1536
|
|
Display
|
RESOLUTIONS SUPPORTED BY DVI
|
|
|
Single-Link DVI
|
Dual-Link DVI
|
|
|
60-Hz LCD with 5% blanking
Interval
|
Up to 1920 x 1080 (HDTV)
|
Up to 2048 x 1536
(QXGA)
|
|
75-Hz CRT with approx. 15%
blanking interval
|
Up to 1280 x 1024 (SXGA)
|
Up to QXGA
|
|
85-Hz CRT with approx. 15%
blanking interval
|
Up to SXGA
|
Up to HDTV
|
DVI
connector classifications
The DVI standard was carefully crafted to
provide a path to the eventual replacement of the analog VGA connector. For
that purpose the DVI interface is composed of two connector types.
The DVI-Integrated (DVI-I) connector, which
can carry a single or dual-link digital signal and/or can carry an analog
signal to support legacy analog devices and the DVI-Digital-only (DVI-D)
connector which can carry a single or dual-link digital signal.
DVI-Integrated
(DVI-I): supports both
analog and digital connections to the display. This 29-pin connector can carry
single or dual-link all-digital video/data signals on 24 pins and uses 5 pins
to carry analog video/data signals and ground. It is easily distinguishable by
the plus-shaped slot surrounded by four pins used to carry the analog signals.
|
COMBINED
ANALOG AND DIGITAL CONNECTOR PIN ASSIGNMENTS
|
|||||
|
Pin
|
Signal Assignment
|
Pin
|
Signal Assignment
|
Pin
|
Signal Assignment
|
|
1
|
T.M.D.S. Data2-
|
9
|
T.M.D.S. Data1-
|
17
|
T.M.D.S. Data0-
|
|
2
|
T.M.D.S. Data2+
|
10
|
T.M.D.S. Data1+
|
18
|
T.M.D.S. Data0+
|
|
3
|
T.M.D.S. Data2/4 Shield
|
11
|
T.M.D.S. Data1/3 Shield
|
19
|
T.M.D.S. Data0/5 Shield
|
|
4
|
T.M.D.S. Data4-
|
12
|
T.M.D.S. Data3-
|
20
|
T.M.D.S. Data5-
|
|
5
|
T.M.D.S. Data4+
|
13
|
T.M.D.S. Data3+
|
21
|
T.M.D.S. Data5+
|
|
6
|
DDC Clock
|
14
|
+5V Power
|
22
|
T.M.D.S. Clock Shield
|
|
7
|
DDC Data
|
15
|
Ground
(return for +5V, Hsync, and Vsync)
|
23
|
T.M.D.S. Clock+
|
|
8
|
Analog Vertical Sync
|
16
|
Hot Plug Detect
|
24
|
T.M.D.S. Clock-
|
|
C1
|
Analog Red
|
C2
|
Analog Green
|
C3
|
Analog Blue
|
|
C4
|
Analog Horizontal Sync
|
C5
|
Analog Ground
(analog R,G, &B return)
|
|
|
DVI-Digital
(DVI-D): supports
digital-only connections between the host computer and display. This interface
is designed for a 12 or 24-pin connection to enable single or dual-link mode
activation.
|
DIGITAL-ONLY CONNECTOR PIN
ASSIGNMENTS
|
|||||
|
Pin
|
Signal Assignment
|
Pin
|
Signal Assignment
|
Pin
|
Signal Assignment
|
|
1
|
T.M.D.S. Data2-
|
9
|
T.M.D.S. Data1-
|
17
|
T.M.D.S. Data0-
|
|
2
|
T.M.D.S. Data2+
|
10
|
T.M.D.S. Data1+
|
18
|
T.M.D.S. Data0+
|
|
3
|
T.M.D.S. Data2/4 Shield
|
11
|
T.M.D.S. Data1/3 Shield
|
19
|
T.M.D.S. Data0/5 Shield
|
|
4
|
T.M.D.S. Data4-
|
12
|
T.M.D.S. Data3-
|
20
|
T.M.D.S. Data5-
|
|
5
|
T.M.D.S. Data4+
|
13
|
T.M.D.S. Data3+
|
21
|
T.M.D.S. Data5+
|
|
6
|
DDC Clock
|
14
|
+5V Power
|
22
|
T.M.D.S. Clock Shield
|
|
7
|
DDC Data
|
15
|
Ground (for +5V)
|
23
|
T.M.D.S. Clock+
|
|
8
|
No Connect
|
16
|
Hot Plug Detect
|
24
|
T.M.D.S. Clock-
|
The DVI connectors have a clever design
feature that allows a Digital-only DVI-D plug to connect to both the DVI-D and
DVI-I receptacle. In contrast the DVI-I plug can connect only to DVI-I
receptacles. This design feature ensures that a Digital-only device is not
connected to an Analog-only device.
High-bandwidth
Digital Content Protection (HDCP)
Future applications for DVI
will include secure digital content delivery. Broadcasters and movie studios
have raised concerns about the possibility of copyright violations now that the
means to deliver high-bandwidth, high-definition content is here. Anyone could
conceivably make perfect copies of copyrighted material. For that purpose the
High-bandwidth Digital Content Protection (HDCP) encryption specification was
developed. HDCP is designed to provide a secure transmission, which provides
copy protection between a DVI video transmitter and a DVI video receiver or
display device. The system will require HDCP-enabled hardware on both the host
graphics system and the display device to provide a protected link. An HDCP
encoding scheme is used to encrypt data at the source, before it is sent to the
display device. The display device will then have to present a set of keys,
which will unlock and allow the display of the digital content.
DVI-Audio
Silicon Image has developed an
audio solution that is fully backwards compatible with the DVI standard. It is
called DVI-Audio and it and it has the bandwidth to support anything from two
channel digital stereo transmitted to HDTV, to 8 channel digital audio or
DVD-Audio transmitted to an A/V receiver. This clever solution works by
embedding the audio signal into the clock signal. DVI-Audio takes advantage of
Transition Minimized Differential Signaling (TMDS) ability to modulate the
position of the falling edge of the clock to send 1 bit of data during each
clock cycle, without affecting the functionality of the display device and
without the need of software drivers. Through this process, a minimum of 25
Mbps can be sent. That is enough bandwidth to support existing digital audio
standards with leftover capacity to support future standards. When transmitting
HDTV resolutions, this capacity is extended to 74.5 Mbps to enable multiple
digital audio channels, well in excess of today’s audio technology.
CONCLUSION
The DVI interface has gained industry wide
acceptance and is considered the industry standard digital graphics interface.
It offers the right combination of versatility and functionality. DVI can be
used to deliver single or dual-link digital video to a display device while
supporting legacy analog devices. Leading market research firms are forecasting
dramatic rises in sales of digital display devices, which will eventually
surpass sales of the current analog display devices. Market surveys indicate
that over 50% of the displays sold in Japan today, are digital. DVI is also
spreading into the consumer market. There are plans to add the DVI connector to
HDTV sets, Set-top boxes, DSS receivers and HD-DVD players. DVI is poised to
replace the analog VGA connector to become the single, universal display interface.
