A/V integration in a wire, no "fire" required
-- EDN, February 1, 2001
Multimedia content of all types is inexorably marching toward an all-digital future. In the process, conventional analog and even low-bandwidth first-generation digital interfaces, such as USB 1.1 and S/PDIF (Sony/Philips Digital Interface), between pieces of computer and consumer electronics equipment are falling by the wayside. In their place, three competing ultra-high-speed digital alternatives are emerging: USB 2.0; IEEE 1394, also called Firewire and i.Link; and the Digital Display Working Group's (http://www.ddwg.org) DVI (Digital Visual Interface), also known as TMDS (transition-minimized differential signaling) or PanelLink (Picture).
Packet-based IEEE 1394, which originated in the consumer-electronics world, has always supported the ability to carry both image and sound data and, with the inclusion of DTCP (digital transmission-content protection), also comprehends media security (see "Media security thwarts temptation, permits prosecution," EDN, June 22, 2000, pg 101). However, the 400-Mbps maximum bandwidth of the current IEEE 1394a version, as with USB 2.0, is insufficient to permit the transmission of uncompressed high-definition video streams. This limitation necessitates clumsy, costly, and quality-degrading multiple decoding and re-encoding steps if, for example, a set-top-box or DVD-player designer desires to superimpose a user-interface display on a decoded DTV signal or MPEG-encoded movie.
The PC industry determined DVI's 165 million-pixel/sec single-channel bandwidth, which is more than adequate for uncompressed high-resolution and high-frame-rate video transfer, and the latest DVI specification iteration also comprehends encrypted transmission. However, until now, DVI has been a video-only protocol, comprising red, green, and blue unidirectional serial channels; a pixel clock; and a low-bandwidth, bidirectional I2C communication link in a single connector. Silicon Image adds high-fidelity, multichannel audio to the mix with its first PanelLink A/V transmitter and receiver, the $5 (50,000) SiI 190 and $12 (10,000) SiI 991, respectively.
The company manages this bit of multimedia magic by modulating the audio bit stream onto the pixel clock. Hollywood will be happy to hear that, as with video, the SiI 190 also supports audio encryption before transmission, and the SiI 991 decrypts on the other end of the link. S/PDIF delivers neither the bandwidth nor the security necessary to carry 9.6-Mbps DVD-Audio content. PanelLink A/V and IEEE 1394a share none of these limitations. PanelLink A/V proof-of-concept demonstrations at last December's Flat Information Display Conference supported a 10-Mbps audio bit rate. Silicon Image believes that production PanelLink A/V silicon should be able to transfer sonic data at speeds as high as 165 Mbps, delivering plenty of headroom for future extensions in audio-sample size and frequency as well as number of channels. PanelLink A/V is backward-compatible with today's video-only DVI and secure-DVI protocols and will append to the DVI specification as an openly licensed industry standard.
The I2C bus, which now enables systems to query and understand the display's maximum resolution, refresh rate, and other features, will deliver additional capabilities in the audio-plus-video era. Transmitters and receivers can interrogate each other to determine whether they both support the A/V protocol and, if not, can alert the user to rely instead on legacy-audio connections, such as analog or S/PDIF. And, if, for example, you prefer to listen to a DVD-Video's DTS (Digital Theater Systems) audio track instead of the Dolby Digital alternative, you can one-time-configure this inclination in your audio decoder. It will then communicate the preference to the DVD player, thereby precluding your having to remember to manually set the audio to the DTS track each time you watch a movie. Silicon Image hopes to make the SiI 190 and SiI 991 available for sampling in the second quarter, and production of both devices is slated for the third quarter.
Silicon Image, 1-408-616-4000, http://www.siimage.com.
-by Brian Dipert
