Digital interfaces promise plug-and-play monitors, flat panels

Digital interfaces promise plug-and-play monitors, flat panels

At the September 1998 Developer Forum, Intel Corp. (Sunnyvale, CA) initiated the formation of the Digital Display Working Group (DDWG) to develop a digital connectivity specification for displays. This working group, a cooperative effort by Intel, Compaq Computer (Houston, TX), Dell Computer (Austin, TX), Fujitsu America Inc. (San Jose, CA), Hewlett-Packard Co. (Palo Alto, CA), IBM Corp. (White Plains, NY), Microsoft Corp. (Redmond, WA), NEC America Inc. (Irving, TX), and Silicon Image (Cupertino, CA), set out to define a connectivity interface and its protocol, electrical, and mechanical specifications.

Five months later, at the Intel February 1999 Developer Forum, held in Palm Springs, CA, the DDWG released the Digital Visual Interface (DVI) specification, which is available on the working group`s Web site (www.ddwg.org). According to Electronic Engineering Times, a number of companies used the forum to demonstrate flat-panel monitors with digital interfaces. These included a 25-in. plasma monitor from Fujitsu; 42-in. plasma and 15-in. LCD monitors from Philips (Eindhoven, The Netherlands); 18-in. LCD monitors from IBM and Compaq; and a 17.3-in. wide-screen monitor from SGI (Mountain View, CA) driven by a graphics board from Number Nine Visual Technology (Lexington, MA).

Intel and Silicon Image also demonstrated what Steve Spina, Intel strategic initiative manager with the desktop products group, called "the first early lab version" of a digital-input CRT, according to Electronic Engineering Times. "Implementation of products compliant with the DVI specification enables developers to immediately save costs by eliminating digital-to-analog-converter functions, while laying the groundwork for the eventual elimination of analog technology altogether," explains Spina.

To incorporate the DVI standard, however, motherboard, frame-grabber, and graphics-display-controller vendors need to incorporate transition-minimized differential signaling (TMDS) technology into their designs. Incorporated into a series of receivers and transmitters known as PanelLink technology from Silicon Image, the DVI specification allows one or two such links to be used depending on the pixel format and timings desired (see figure above).

In operation, the pixel- and monitor-control data from a digital graphics controller are first encoded using a TMDS transmitter and then sent to a TMDS receiver and display controller located in the monitor. There, the data are decoded back into pixel and control data to drive a display controller or a DAC, according to the DVI specification. For a CRT to display the same pixel format as a reduced blanking flat-panel monitor, the high-retrace requirement of the CRT places a high-bandwidth requirement on the graphics subsystem. In such cases, two TMDS links can be used to support pixel formats of greater than 2.75 million pixels at an 85-MHz refresh rate.

Monitor manufacturers and graphics-display-controller vendors are readily accepting the technology. At the July 1999 PC Expo trade show in New York City, ViewSonic (Walnut, CA) previewed its "digital-only" roadmap to migrate its 15-, 17-, 19-, and 21-in. CRTs and LCDs to digital technology. Also in July, Matrox Electronics Systems Ltd. (Dorval, Quebec, Canada) unveiled its G200 Multi-Monitor Series, a single PCI graphics card that supports as many as four DVI-based digital flat-panel displays. This series features an integrated 250-MHz RAMDAC and a Silicon Image 154 PanelLink transmitter on each MGA-G200 chip. Combined with 8 Mbytes of SGRAM for each output, the board can display a variety of resolutions to a maximum of 1800 x 1440 pixels for analog flat panels and monitors and 1280 x 1024 pixels for digital units.

In August, Number Nine Visual Technology introduced its SR9 graphics accelerator, a PCI-based graphics controller board capable of providing digital signals for displays with resolutions to 1280 x 1024 pixels. Providing built-in support for monitors and digital LCD displays, the board uses snap-on digital interface modules to support DVI-enabled displays.

Intel would like suppliers to integrate DVI into every new PC and, at the same time, phase out the traditional VGA connector. Like the IEEE-1394 (FireWire) digital camera interface, the DVI approach would place the burden of integrating analog functions into external components (in this case, the display). While this integration eliminates analog development problems for motherboard vendors, it places a greater development burden on monitor manufacturers, who must now implement digital-to-analog design techniques into high EMI/RFI environments. Such design factors could slow the rapid introduction of "digital" monitors using the DVI specification.