An Introduction to DVI and Digital Connectivity

These days new connector

types are showing up with alarming

frequency on all types of consumer

electronics equipment. Whether

you look on notebooks or desktops,

DVD player s, cable boxes or satellite

receivers, or even on TV’s, ?at panel

displays or projectors, one is likely

to encounter a bewildering array of

connectivity designed, it seems, just

to confuse us.

In the evolving world of

high-tech displays, new connector

types also abound, but most are of

great significance and value to con-

sumers. This is especially true with

the latest wave of digital video con-

nections found on everything from

today’s newest ?at panel monitors to

HDTV sets.

The technology behind these

connections allows for a direct digital

interface between your source and

your display, which provides stellar

pixel-for-pixel accuracy, and im-

proved image quality that is simply

impossible to achieve with conven-

tional analog technology. If one

peers more deeply, you’d see that

inside your computer the video in-

formation is processed digitally and

sent to the display. In the old days,

CRT monitors would process the sig-

nal in the analog domain; however,

with today’s ?at panel display, this

processing is done digitally. The pro-

cess of converting the digital signal

in the PC from digital to analog and

then back to digital again is incred-

ibly inefficient and results in noise,

sampling errors and other artifacts

that can visibly degrade the picture

quality. In an all-digital system, the

signal stays digital from the PC to

the display without the need to be

converted to the analog domain.

Eliminating this circuitous conversion

process results in noise-free images

with perfect color and pixel-perfect

accuracy.

In addition to more accurate

transmissions, digital connectivity

also allows for higher bandwidth

transmissions, which equates to

greater on-screen resolution. As

higher resolution sources and

displays are created, bandwidth

transmission through traditional

analog cables becomes more prob-

lematic. In most applications, the

cable becomes the limiting factor as

its internal capacitance acts like a

low pass filter, degrading the signal

bandwidth (especially high frequen-

cies) as cable lengths are increased.

At the forefront of PC-based

digital displays is a connectivity stan-

dard known as DVI (Digital Visual In-

terface). DVI comes in two “classes”:

single and dual link. Just to make

things interesting, it is also impor-

tant to note that DVI comes in three

different “formats”: DVI-D (digital

only), DVI-I (digital and analog), and

the so-called DVI-A (analog only).

The reason for these permutations

was that originally the DVI-I format

was designed to be a backward-

compatible format that could provide

support for older analog equipment

such as CRT monitors. Whereas the

DVI-D and DVI-A formats have only

one (digital or analog) signal pres-

ent, the DVI-I for mat has both an

analog and a digital signal available

concurrently. Because of this ?ex-

ibility and improved performance

DVI has been well received as a new

connectivity standard.

Connectivity Reference Table

Connector Style

Male (Plug)

Female (Receptacle)

HDMI

M1

DVI-D Single Link

DVI-D Dual Link

DVI-I Single Link

DVI-I Dual Link

Technology Connection: Issue 1                                               -1-                                               October 1, 2004

© Copyright 2004 DVIGear

Single link DVI supports

a bandwidth of up to 165 MHz,

whereas dual link can support a

bandwidth of twice that (up to 330

MHz). To approximate your band-

width requirements, you can simply

multiply your horizontal resolution

by your vertical resolution by your

refresh rate. For example, if your

PC is running at XGA resolution

(1024x768) with a 60 Hz refresh

rate (see your monitor settings on

the Control Panel), then 1024 x

768 x 60 = 47,185,920 or about 47

MHz. Since this is less than 165

MHz, we can correctly deduce that

a standard XGA display signal will

easily transmit over a single link DVI

connection. In fact, a single link DVI

connection can support standard

HDTV at 720p and 1080i, as well as

full 1080p HDTV resolution (1920 x

1080 x 60Hz = 124 MHz)! Dual link

DVI connections can support QXGA

(2048x1536) and beyond without

any problems. Furthermore, the

newest DVI processor chips will

extend this range to even greater

bandwidth at single (225 MHz) and

dual (450 MHz) link resolutions. For

most consumer applications today,

single link DVI is more than suf-

ficient, but that could change in the

future…

With greater bandwidth ca-

pabilities, cable length limitations will

become even more critical. Cur rent-

ly, the standard specification for DVI

is up to 5 meters (16.4 ft.). However,

high quality copper cables and also

fiber optic cables are available that

can transport the DVI signal to much

greater distances. Fiber cables can

easily transmit a DVI signal 100

meters (328 ft.) and beyond! While

copper DVI cables are usually limited

in length, electronic repeaters can

be used to electrically re-generate

the signal, thus allowing it to be

sent further distances. A repeater

accomplishes this task by receiving

the incoming signal and then recon-

structing a pr istine copy that is opti-

mized for re-transmission down long

cable r uns. Using this

approach, repeaters have

been used to send DVI

signals hundreds of feet

when properly placed

in the signal chain. The

main drawback of using

fiber cables or even repeaters is the

cost associated with these products.

In the past, there have been

only a few manufacturers that could

supply DVI cables with lengths over

5 meters. However, more recently,

some manufacturers (e.g., DVIGear)

have introduced high performance

copper cables that can work well up

to 15 meters (49 ft.). Currently it

is possible to send a high resolution

image of 1600x1200 @ 60 Hz across

a 15 meter DVI cable with little to no

signal degradation.

While DVI is a popular digi-

tal display connector, it is certainly

not the only type in use today. There

are many connector types in circula-

tion, including: DFP, M1, P&D, LVDS,

OpenLDI, and ADC to name a few.

One of the older connector

types that is in circulation, but isn’t

appearing on new devices is the

DFP type, also known as the MDR20

standard. The DFP connector’s de-

mise is largely attributable to its lack

of versatility based on two factors: it

only offers single link bandwidth and

it is digital-only.

One standard that increas-

ingly more popular is the M1 (a.k.a

EVC or P&D) standard. This connec-

tor allows for the same capabilities

as DVI-I, that is to say, digital single

or dual link, plus analog transmis-

sions. But in addition, the M1 con-

nector also supports USB (control)

and FireWire. These added capabili-

ties are attractive to manufacturers

of compact business projectors such

as InFocus, Dell and HP as these

connectors offer great ?exibility and

take little space on an input panel.

ADC or the Apple Display

Connector is yet another format

which is a proprietary design created

by Apple Computers. It combines all

of the capabilities of the M1 stan-

dard – digital single or dual link or

analog transmissions, USB (control),

and FireWire. However, ADC also

includes the ability to power the

display through the connector. This

allows displays with the ADC con-

nector to have one total connection

which allows for a sleek and simple

looking display setup.

On the technical side, a

common thread of all these connec-

tivity standards is that they are all

based on Panel Link Technology from

a company called Silicon Image.

This commonality allows can provide

DFP Female Connector

ADC Male Connector

SGI 1600SW Monitor

Samsung HD931 - DVI Enabled DVD Player

Technology Connection: Issue 1                                               -2-                                               October 1, 2004

© Copyright 2004 DVIGear

an easier means of signal adaptation

from one format to another. When

converting display signals to other

non-Panel Link based standards, it

can become more costly, and there

are more chances for signal degra-

dation.

One non-Panel Link based

technology is the OpenLDI, LVDS,

or MDR-36, which proprietary to SGI

(Silicon Graphics). This connector

appears on SGI’s 1600SW monitor, a

very popular digital monitor. Howev-

er, for this monitor to be connected

to a VGA, DVI, or any other digital

source, the signal must pass through

a SGI Multilink Adapter, which is no

longer being manufactured. Be-

cause OpenLDI is not based on

Panel Link technology, it is no longer

being used by SGI and will eventu-

ally completely die out.

Coming back again to DVI

connectivity, there are other more

subtle aspects that should be men-

tioned. One aspect that is getting

a lot of attention in the world of

consumer electronics is HDCP (High-

bandwidth Digital Content Protec-

tion). Created by chip giant Intel,

HDCP is an encryption technology

designed to protect digitally trans-

mitted picture content from illegal

copying and distribution. Backed

by content producers (studios)

who strongly desire to protect their

investments (e.g. movies, sport-

ing events, TV shows, etc.), HDCP’s

underlying charter is to protect and

maintain control of copyrighted

materials. It does so through the

use of an encryption process that

renders the signal unusable unless

a special HDCP decoder is used to

decrypt the signal. This decoder re-

lies on the use of special cipher keys

which must be implanted in all HDCP

devices (transmitter s and receiv-

ers) so that they can “talk” to each

other in a secure fashion; however,

a difficulty arises when a non-HDCP

compliant device is added into the

signal chain. For information on

HDCP, see DVIGear’s article entitled:

“HDCP – For Better or for Worse.”

Another noteworthy point

of DVI technology is a tiny piece of

information contained within the DVI

signal known has EDID (Extended

Display Identification Data). EDID

is small block of data that contains

fundamental information about a

display (monitor, projector, plasma,

LCD, etc.) and its capabilities. The

EDID data can include: vendor

information, maximum image size,

color character istics, factor y pre-

set timings, frequency range limits,

and character strings for the moni-

tor name and serial number. Some

computers require the receipt of this

EDID information in order to work

properly. In addition, the EDID infor-

mation allows a computer source to

optimize its output for a particular

display. In some applications where

the sources needs to see the EDID

data and something in the applica-

tion is prohibiting this information

from being sent, there are devices

that exist that can store the infor-

mation and trick the computer into

thinking that the display is set up

a certain way, allowing the applica-

tion to work properly. These EDID

devices can solve many mysterious

problems that otherwise can baf?e

even the most seasoned experts.

For more infor mation, please call

DVIGear application support.

In closing, let’s take a look

at a new a rapidly-growing form

of digital connectivity called HDMI

(High Definition Multimedia Inter-

face). Yet another digital connectiv-

ity acronym, you’ ll surely be hearing

more about HDMI in the future. A

direct outgrowth of DVI, the HDMI

connector is deceptively small and

looks more like a jumbo USB type

connector. Nonetheless HDMI offers

a formidable array of signal connec-

tions, including all forms of digital

video (HDTV), PCM digital audio

(7.1) and bi-directional communica-

tion for remote control functions.

HDMI is fully HDCP compliant and

is 100% backward compatible with

DVI. HDMI is truly revolutionary in

that it allows for interconnection of

sources, receivers and displays, all

using a single cable type for digital

audio, video and control. Today

more and more consumer electron-

ics devices are appearing with HDMI

connectivity. HDMI cabling solutions

are somewhat more robust than

DVI and the connector’s smaller

form factor has been well received

by installers as it is easier to route

through internal structures. For

more information on HDMI, please

see DVIGear’s article entitled:

“Smaller Connector, Bigger Options”.

If you are interested in

lear ning more about digital connec-

tivity or have a special application

request, please contact DVIGear for

more information.

Technology Connection: Issue 1                                               -3-                                               October 1, 2004

© Copyright 2004 DVIGear