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Exploring Embedded DisplayPort

Posted: 18 May 2016     Print Version  Bookmark and Share

Keywords:the Video Electronics Standards Association  VESA  Embedded DisplayPort  eDP  LVDS 

Today's personal electronic devices continue to get smaller and easier to use, with more performance and functionality. Such advances are often driven by technology hidden from the consumer, behind the sleek industrial design and elegant user interface. Video quality improvements are one example. A "better" display is normally equated to more pixels per inch driven by a multi-core GPU that supports high-resolution rendering. But "better" can also be one that uses less power to extend battery life, interferes less with wireless service to enable better coverage, and improves chip integration to enable sleeker, lighter-weight system designs.

VESA recently announced an update to the eDP Standard. Called eDP v1.4b, this new version puts the finishing touches on the eDP v1.4 Standard that was released in February 2013. Panels capable of supporting eDP v1.4b are now in production, and eDP v1.4b will be enabled in 2016 notebooks. eDP v1.4b includes several enhancements to enable improved flexibility of system implementation, reduced device complexity and lower bill of materials (BOM) costs. However, before we get into what's new for eDP v1.4b, let's look back at why the eDP Standard was first developed, and how it has affected the electronics ecosystem through the collaborative efforts of VESA member companies that continually evolve this standard and propagate it across the supply chain.

Figure 1: At display resolutions beyond Full HD (1920x1080) or Full HD+ (1920x1200), eDP has a significant advantage over LVDS in minimizing the number of high-speed wire pairs needed in the display interface, which in turn results in reduced total system footprint. (Source: VESA)

Creating the foundation for eDP
eDP was first introduced in late 2008 as a simplified version of DisplayPort for internal displays. The main goal was a common display interface that could be used for both external and internal displays. Shortly thereafter, the main GPU / CPU vendors, including Intel, NVIDIA and AMD, announced that eDP would replace the current (at that time) LVDS interface standard, and that LVDS support would go away, which it now has. The motivation was simple: The chip industry needed to replace the high-voltage LVDS interface with one that could drive integration and display performance. eDP became the obvious choice because it could repurpose the flexible and extensible DisplayPort interface—meaning the same video port could drive an internal or external display, enabling platform application and design flexibility.

Through subsequent releases of the eDP standard over the last several years, the computer industry OEMs involved with the standard have continued to make refinements unique to eDP and not shared by DisplayPort, at least not at the time. eDP v1.0, which was released in 2008, was basically a simplified version of DisplayPort with a definition of panel power sequencing. In late 2009, eDP v1.1 added system power management enhancements through the introduction of video frame rate control. One of those particular methods later became the Adaptive-Sync feature, now supported by DisplayPort (figure 2). This was followed by the release of eDP v1.2 in 2010 with a new set of commands sent over the AUX Channel—the sideband bus used for both DisplayPort and eDP—to control other aspects of the display, including backlight brightness and color rendering characteristics. This eliminated the need for other control signals, removing several pins and wires in the display interface. And then in eDP v1.3, published in early 2011, new display protocols were added to enable Panel Self Refresh (PSR), which adds a separate frame buffer to the display and allows the host GPU / CPU to enter a low power state when a static display image is encountered, which is surprisingly often. This feature further reduces power and extends battery life.

Figure 2: Application of Adaptive-Sync to frame rate reduction (top); application of Adaptive-Sync to game rendering (bottom). (Source: Parade Technologies; galloping-horse photos by Eadweard Muybridge, 1887)

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