The Digital Visual Interface (DVI) specification, introduced in April of 1999, established an industry-wide standard for an interconnecting link between a video source and a digital display. Using this, Silicon Image has crafted the SiI 168 PanelLink HDCP transmitter and the companion SiI 861 PanelLink HDCP LCD monitor controller. According to the company, this is the first transmitter-receiver pair to include content protection in a DVI link. This pair of ICs provides 5 Gbits/s of bandwidth to transmit protected high-definition video content without costly, complex video compression.
Even before the advent of content protection, DVI was attractive because an all-digital interface was clearly the path to follow. DVI does away with cascaded analog-to-digital and digital-to-analog conversions. Also, it provides improved, consistent image quality to all display technologies. Even CRT monitors are implementing the DVI interface to realize the benefits of a digital link. The image is sharper because there are fewer errors and less noise.
Digital flat-panel monitors require no analog-to-digital conversion, so they're less expensive than analog flat-panel displays as well. Confirming DVI's appeal, Silicon Image has shipped 10 million PanelLink transmitters and receivers without the content-protection feature over the past three years.
High-bandwidth digital content protection (HDCP), a program devised by Intel, is making DVI even more enticing. This DVI companion protects data flowing over a DVI link, from a video source (such as a PC, set-top box, DVD player, or digital VCR) to a digital display (such as an LCD monitor, television, plasma panel, or projector), so that the content cannot be copied.
HDCP also answers a plea from the entertainment industry, particularly from the studios that provide much of today's premium content. They have been seeking a content-protected solution for transmitting premium data to the next generation of digital television sets. Members of the Motion Picture Association have endorsed the HDCP specification, paving the way for the release of high-definition, digital-video content to consumers in the form of DVDs, HDTV broadcasts, and eventually the Internet. Digital displays such as LCD monitors will become linked to desktop computers, DVD players, set-top boxes, and other technologies.
Data encryption is applied at the DVI transmitter's input (Fig. 1). Decryption occurs at the DVI receiver's output. The available bandwidth is not compromised by HDCP's implementation.
To maintain the output data stream's stable, average dc value, the DVI interface uses a transition-minimized, signaling protocol developed by Silicon Image. Transition minimization is implemented by an encoding algorithm that converts 8 bits of data into a 10-bit, transition-minimized, dc-balanced character for data transmission over copper and fiber-optic cables. Transmission over the DVI link is serialized, so the technology is optimized for reduced EMI across copper cables. The clock recovery at the receiver exhibits high skew tolerance, enabling the use of longer cable lengths, as well as shorter low-cost cables.
A more concretized version of the DVI link appears in Figure 2. A source, designated the graphics controller, supplies data via the SiI 168 PanelLink HDCP transmitter. In turn, the transmitter is linked to the digital display via the SiI 861 PanelLink HDCP LCD monitor controller. The data stream comprises both pixel and control data. It flows over the link, which is made up of four channels. Channels 0, 1, and 2 are assigned to the red, green, and blue data. The fourth, channel C, carries the interface clock and control signals.
Each DVI channel in a single-link configuration can handle up to 1.65 Gbits of pixel data, providing 4.95 Gbits/s of total bandwidth for the link. This permits the use of SXGA (1280 by 1024) pixels at an 85-Hz refresh rate for a CRT, UXGA (1600 by 1200) pixels at a 60-Hz refresh rate for an LCD, and HDTV resolution of 720p (progressive) and 1080i (interlaced) lines for high-definition televisions and projectors.
To support higher resolutions—such as 2048- by 1536-pixel, high-end, PC workstation monitors—two links can be integrated into a single DVI connector interface. This supports a bandwidth of 330 Mpixels/s and above. The dual link comprises six channels and a shared clock. The amount of bandwidth required by a specific display at a given resolution is technology-dependent, relying on blanking overhead, refresh rate, color depth, and other factors.