Background:

As the HDTV market continues to heat up, consumers are in need of being educated on the latest technology in order to make intelligent purchasing decisions. There are a plethora of articles explaining the technical pros and cons of the 3 dominant HDTV display technologies namely: LCD, Plasma, and DLP. However, one all- important, but overlooked feature in selecting a HDTV set is the type of HD video connection. The video connections available for HDTV are: component video, DVI (digital video interface) and HDMI (high definition multi-media interface). We will discuss briefly the pros and cons of each.

Component video cable commonly referred to as R, G, B (Red, Green, Blue) actually consists of 3 separate cables because it distributes the 3 primary color components to the display. All colors can be generated from weighted distribution of each Red, Green and Blue color components. Of the 3 HD connection technologies available today, analog component video is the most mature technology. Each cable has a characteristic impedance of 75 ohms like standard coaxial cable.

• Advantage: Analog component video cable is mature and cost effective.
• Disadvantage: component video cables are analog! All HDTV sets are inherently digital therefore extra digital to analog and analog to digital conversion is necessary in order to process the video. This extra conversion can introduce video artifacts. Since all HDTV's are digital, it only makes sense to use an all- digital connection such as DVI or HDMI.

DVI(digital video interface) as the name suggests is an all-digital video connection. Unlike analog component cables the DVI interface transports the original digitized R,G, B video signals from the HD source to the HD display. Since it all digital, no artifacts or degradation will be incurred. You will get EXACTLY the picture that the video source supplies with no degradation. DVI connection is often found on HDTV as well as PC video cards.

• Advantage: DVI is ALL-digital, so there is no picture degradation from source to display.
• Disadvantage: Digitizing R, G, B requires extremely high bandwidth. The aggregate data rate of the digital R, G, B signals is 1.65 Gbps! The high bandwidth means that cable quality is important and also the link distance is limited. Typical link budget for a DVI is ~ 15 ft.

DVI cable

HDMI (high definition multi-media interface) is the latest state of art audio and video connection. Technically, HDMI is identical to DVI with 3 notable differences. 1) HDMI is a much smaller connector (it looks like an U.S.B. connector), 2) HDMI utilizes copy protection called HDCP (high definition copy protection) and 3) HDMI carries multi channel digital audio. HDMI, like DVI, is ALL-digital therefore picture quality is “perfect” from source to display.

• Advantage: HDMI is a single digital video and Audio connection. Only 1 single cable is needed to transport both audio and video! This significantly reduces cable clutter behind your theater setup. HDMI is all-digital therefore there is no picture degradation from source to display.
• Disadvantage: Like DVI, the link distance is limited and a high quality cable is required because of the inherently high bandwidth required to transport digital R, G, B. video.

HDMI cable

HDMI to DVI: is a hybrid of HDMI and DVI. For now, there is a mix of both DVI and HDMI equipment on the market. For example, you may have a DLP projector that has a DVI input, but your new DVD player has a HDMI output. You can simply connect the 2 devices by using a HDMI to DVI cable and receive digital video. The reason is that HDMI is backward compatible with DVI.

HDMI to DVI cable

Conclusion:

As the HDTV market continues to mature, consumers will need to be educated on the HDTV video connections available. We have outlined briefly the main features along with the pros and cons of each connection solution, so the consumer can make intelligent choices in selecting the HDTV video connections.

References:

"Digital Visual Interface & TMDS Extensions" Silicon Image, Sunnyvale, CA 94085

"High-Bandwidth DIgital Content Protection " Silicon Image, Sunnyvale, CA 94085

"High Definition Multimedia Interface,HDMI Specification 1.2" HDMI LLC.