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What is DisplayPort?

In late 2003 a group of leading PC, graphics and semiconductor companies got together to plan a new digital display interface standard to meet future demands on the interface and to reduce display cost and complexity. The goal was to develop an open standard based, royalty free and extensible interface suited for both external desktop monitor and internal display interfaces, and to have it ready for implementation in products in 2006.

This group was the start of the Video Electronics Standard Association (VESA) which is an international non-profit corporation that supports and sets industry wide interface standards for the PC, workstation and consumer electronics industries.

The new interface would replace the proprietary digital visual interface (DVI) used between the PC and an external display. This interface could not be updated and had physical, functional and cost limitations that inhibited its suitability for future needs. The DisplayPort standard specifies a high bandwidth, bi-directional display interconnect that enables a common interface approach for internal and external display connectivity. The DisplayPort interface features optional audio capability.

This standard provides an open and extensible royalty free specification that meets the current and future needs of the PC industry without the restrictions associated with the other interfaces technology.

DisplayPort Versions

The first generation of DisplayPort provided over 10.8Gbps of raw bandwidth, which no other display interface could match. DisplayPort also supported very long non -active cables, optional latch designs for connectors and audio support. In addition, with DisplayPort spread spectrum clocking can be enabled to reduce EMI, and souce devices such as GPUs can operate in dual-mode.

The latter is valuable for it allows the same connector to transport TMDS signals to Support DVI and HDMI outputs using inexpensive level shifting adapters.

The data link rates of DisplayPort 1.1 are fixed at either 1.62Gbps per lane or 2.7Gbps per lane, irrespective of the timing of the attached display device. This design only requires a single reference clock source to drive as many DisplayPort streams as there are display pipelines in the GPU.

In contrast DVI and HDMI both require a dedicated clock source per display timing. This unique DisplayPort feature allows for the most efficient multi-display design and complements AMD Eyefinity multi display technology. In early 2010 the DisplayPort 1.2 specification was confirmed by VESA, this new revision of the standard adds support for new and exciting feature , including High Bit rate audio even higher bandwidth from 10.8Gbps to 21.6Gbps and multi stream capabilities.

In the last quarter of 2014 the DisplayPort 1.3 was approved which increased bandwidth to 32.4Gbps with the new HBR3 mode featuring 8.1Gbps per lane up from 5.4Gbps with HBR2 in version 1.2

In March 2016 the DisplayPort 1.4 was published, it still uses HBR3 mode but adds supports for Display Stream Compression 1.2 (DSC) and the next generation for DisplayPort will improve link rate from 8.1 to 10Gbps which will increase total bandwidth from 32.4 to 40 Gbps .

Version 2.0

DisplayPort 2.0, which was introduced in June 2019, provides up to a 3X increase in data bandwidth performance compared to the previous version of DisplayPort, as well as new capabilities to address future performance requirements of displays. These include beyond-8K resolutions, higher refresh rates and high dynamic range (HDR) support at higher resolutions, improved support for multiple display configurations, as well as improved user experience with augmented/virtual (AR/VR) displays, including support for 4K-and-beyond VR resolutions. Featuring the highly efficient 128b/132b channel coding shared with USB4, DisplayPort 2.0 delivers a maximum payload of 77.37 Gbps across four lanes (up to 19.34 Gbps per lane)—supporting ultra-high display performance configurations such as an 8K (7680×4320) display with 60Hz refresh rate with full-color 30 bpp 4:4:4 HDR resolution uncompressed, and 16K (15360×8640) 60Hz display with 30 bpp 4:4:4 HDR resolution with compression. With the release of DisplayPort Alt Mode 2.0, all of these high-performance video capabilities are now available to the USB ecosystem.

DisplayPort, Mini DP and Thunderbolt Connectors

Talking about versions, specifications and standards.

The first generation of DisplayPort™ versions initiated back in 2006 with version 1.0 which was hardly implemented in commercial products. The latest standard of DisplayPort™ is the 2.1 version. Providing up to 80 Gbps of bandwidth to meet the highest demands of up to 16K display resolution.

The most important to notice here is raw bandwidth. The current versions of DisplayPort™ – 1.2,1.3 & 1.4 – offer up to 32.4 Gbps of bandwidth – or 25.9 Gbps after overhead – which is sufficient for a standard 16.7 million color (24-bit) 4K120Hz display, or up to 98Hz for 1 billion+ color (30-bit) displays (Overhead Is the efficiency to En- or De-Code the data stream by using different algorithms). This is an overwhelming growth of raw bandwidth, almost 2.5 times that of version1.3/1.4, but it still isn’t enough for the coming generation of 8K or even the new 16K displays. As a result, the need for more display interface bandwidth continues to grow.

When we look closer at the improvements in version 2.0 a more efficient coding scheme, resulting in much less coding overhead was introduced. As a result, the effective bandwidth of the 2.0 standard will peak at 77.4 Gbps, this is almost the full available bandwidth!

DisplayPort 2.0 Under the Hood: Thunderbolt 3, UHBR, etc.

Diving a bit deeper into the technical aspects of DisplayPort™2.0 physical layer. Developing the next generation of high bandwidth external interfaces only gets harder and more expensive with each generation. At the same time, the physical DisplayPort wasn’t originally designed to scale up to the amount of bandwidth DisplayPort 2.0 will be pushing.

The end result then is an interesting compromise, and importantly, one that delivers more bandwidth while retaining backwards compatibility with existing DisplayPort products. The DisplayPort itself is staying: it and the USB-C connector (via DP alt mode) are both official ports for the new DisplayPort 2.0 standard. And because of this, the number of pins and resulting high speed data lanes is remaining unchanged as well, with DisplayPort continuing to operate over 4 lanes. Finally, the DisplayPort 2.0 standard also retains the technology’s packet-based approach to communications, which means that image data continues to be sent as packets over a fixed bandwidth link, as opposed to pixel-centric pixel clock approaches.

So what has changed to enable DisplayPort 2.0?

While the titular DisplayPort itself has stayed, the rest of the physical layer has been almost entirely replaced… with Thunderbolt 3.

Rather than attempting to reinvent the wheel, for DisplayPort 2.0 VESA decided to take advantage of Intel’s existing Thunderbolt 3 technology, which already hits the data rates that VESA was looking for. While initially a proprietary Intel technology, Intel released the technology to the wider industry as a royalty-free standard early 2019.

This allowed third parties to not only create pure Thunderbolt 3 devices, but also allowed Thunderbolt 3 technology to be repurposed for other standards. So whereas USB4 is a more straightforward rebranding of Thunderbolt 3, for DisplayPort 2.0 takes it in a different direction by essentially creating a one-way Thunderbolt 3 connection.

Under the hood

Thunderbolt 3 operates fairly similarly to DisplayPort, with 4 high-speed each lanes carrying packets of information at 20 Gbps. However while TB3 is a true bi-directional, full-duplex link with 2 lanes allocated for each direction, DisplayPort is focused on sending large volumes of data in just one direction: out. As a result, DisplayPort 2.0 reverses the two inbound lanes to outbound lanes, allowing the four total lanes to be combined into a single 80 Gbps link.

The move to Thunderbolt 3 technology also means that DisplayPort inherits Thunderbolt 3’s signal encoding scheme. Whereas DisplayPort 1.x has always used relatively inefficient 8/10b encoding – resulting in 20% overhead – DisplayPort 2.0 will offer 128/132b encoding, which has just 3% overhead. This is why the practical bandwidth gains for DisplayPort 2.0 are more than just the raw bandwidth gains; the standard doesn’t just get more bandwidth, but it uses it more efficiently. Consequently, at its highest data rate, DisplayPort 2.0 will be able to offer 77.37 Gbps of bandwidth.

But what of cables?

Here’s where things get a bit trickier, both for VESA and for users. Thunderbolt 3 pushed the limits of copper cabling, and as a result for all but the shortest runs it requires active cabling, with transceivers at each end of a cable. While effective, this drove up the cost of Thunderbolt 3 cables versus relatively lowcost all-copper commodity USB 3 and DisplayPort 1.x cables. By using Thunderbolt 3 as the basis of their new standard, VESA has inherited the cable technology limits of the standard as well.

The answer to the cable question then is that VESA hasn’t really answered it. Instead, they’re focusing on what they can do now with passive cables

DisplayPort 2.0 actually introduces not one, but three new data rates: 10 Gbps per lane, 13.5 Gbps per lane, and 20 Gbps per lane. Dubbed Ultra High Bit Rate (UHBR), the for free-standing monitors VESA right now is focusing on 10 Gbps per lane (UHBR 10), which will deliver a total of 40 Gbps of bandwidth.

At just half the data rate of full-fat DisplayPort 2.0 (and Thunderbolt 3), UHBR 10 is resilient enough that it can operate over standard passive copper cabling, and cables should have little issue reaching 2-3 meters. VESA has actually been preparing for this for some time now, and UHBR 10 aligns with their previously-launched DisplayPort 8K cable certification program; 8K-certified cables will be able to meet the signal integrity requirements for UHBR 10.

Forward Error Correction (FEC), which was introduced to DisplayPort 1.4 as part of the Display Stream Compression (DSC) standard, is now a core part of DisplayPort 2.0. So on a 2.0 link, FEC will be in use at all times, reflecting the challenge in getting these high speed interfaces to constantly transmit data in an error-free manner.

DisplayPort 2.0 Features: Mandatory DSC, Branch Devices, & Panel Replay

Display Stream Compression support is now mandatory for DisplayPort 2.0 devices. Previously introduced as part of DisplayPort 1.4 – and not really hammered out entirely until a couple of years after that – DSC is the group’s standard for “visually lossless” image compression. Operating on small groups of pixels, DSC offers compression ratios of around 3:1, with the goal of compressing images just enough to save power and bandwidth without introducing visual artifacts and without adding significant latency.

At any rate, starting with DisplayPort 2.0, DSC is now a core part of the DisplayPort standard. To be clear, 2.0 devices do not have to use DSC – the preference is clearly towards uncompressed images when the bandwidth allows for it – however 2.0 devices must be able to encode, pass, and decode DSC compressed data. This will, over time, lay the groundwork for manufacturers to develop and release monitors that require DSC (at least in certain modes), as they’ll be able to sell monitors knowing that all 2.0 devices can drive them.

Panel Replay

Speaking of efficiency, the DisplayPort 2.0 standard is also introducing another vendor-optional feature focused on power efficiency, and that’s Panel Replay. Derived from earlier Panel Self Refresh technologies that are part of the embedded DisplayPort standard, Panel Replay is a partial self-update mechanism that allows a system to only transmit and update the portion of an image that has changed since the previous video frame. Like PSR in eDP, this feature is primarily intended for laptops and other mobile devices, where power consumption and the resulting impact to battery runtimes are important qualities. Transmitting less data reduces not only the amount of energy used chauffeuring bits around, but it also reduces the amount of processing required in a display controller.

Last but not least, DisplayPort 2.0 is also updating how “branch devices” work in the standard. Essentially the splitters in a Multi Stream Transport setup, DisplayPort 1.x required that the branch device be capable of decoding a DisplayPort bitstream, which is not an easy feat with 20 Gbps+ of data. So instead, for 2.0, branch devices are being simplified some, and now will just be able to forward data rather than having to decode it. This should make MST (and daisy chaining) a bit easier to implement overall, as branch devices won’t need to be as complex.

On a final note, ahead of today’s specification release I also asked about the state of variable refresh support on DisplayPort. VESA Adaptive Sync is an optional feature for monitors under DisplayPort 1.x, and it will remain so under DisplayPort 2.0. So manufacturers can continue adding it as a useful feature for their monitors, but there are no plans to make it mandatory.

The latest version of the DisplayPort standard is easily the biggest update to the PC display standard since it launched in 2007. By replacing the DisplayPort physical layer with Thunderbolt 3, VESA has greatly increased DisplayPort’s bandwidth potential, laying the groundwork for 8K monitors and beyond.

Latest DisplayPort specification provides greater alignment with USB Type-C and USB4; adds new features for more efficient DisplayPort tunneling over USB4.

Evolution of DisplayPortTM Data Bandwidth

BEAVERTON, Ore. – October 17, 2022 – The Video Electronics Standards Association (VESA®) announced today that it has released DisplayPort 2.1, the latest version of the DisplayPort specification, which is backward compatible with and supersedes the previous version of DisplayPort (DisplayPort 2.0). VESA has been working closely with member companies to ensure that products supporting DisplayPort 2.0 would actually meet the newer, more demanding DisplayPort 2.1 spec. Due to this effort, all previously certified DisplayPort 2.0 products including UHBR (Ultra-high Bit Rate) capable products – whether GPUs, docking station chips, monitor scalar chips, PHY repeater chips such as re-timers, or DP40/DP54/DP80 cables (including both passive and active, and using full-size DisplayPort, Mini DisplayPort or USB Type-C connectors) – have already been certified to the stricter DisplayPort 2.1 spec.

For more information on VESA, please visit http://www.vesa.org/

DisplayPort 2.1

The major change in v2.1 is to have a better understanding of the 3 different speeds supported, DP40, DP54 and DP80. DisplayPort 2.1 has also updated the DisplayPort cable specification to provide greater robustness and enhancements to full-size and Mini DisplayPort cable configurations that enable improved connectivity and longer cable lengths (beyond two meters for DP40 and DP54 cables and beyond one meter for DP80 cables) without diminishing UHBR performance. VESA certified DP40 cables support up to the UHBR10 link rate (10 Gbps), with four lanes, providing a maximum throughput of 40 Gbps, DP54 cables support up to the UHBR13.5 link rate (13.5 Gbps), with four lanes, providing a maximum throughput of 54 Gbps, while VESA certified DP80 cables support up to the UHBR20 link rate (20 Gbps), with four lanes, providing a maximum throughput of 80 Gbps.

Due to the higher speed(read frequencies), the physical layout of the DisplayPort connectors(both MiniDP and DP) had to be adjusted in order to prevent crosstalk and jitter. All of these changes have been made to accomodate the current pin layout and physical dimension of both these connectors and are normally referred o as "Enhanced Connectors".

Achieving a robust, end-to-end user visual experience remains the utmost priority for VESA’s DisplayPort specification, whether across a native DisplayPort cable, via DisplayPort Alt Mode (DisplayPort over the USB Type-C connector), or tunneled through the USB4 link. As such, DisplayPort 2.1 has tightened its alignment with the USB Type-C specification as well as the USB4 PHY specification to facilitate a common PHY servicing both DisplayPort and USB4. In addition, DisplayPort 2.1 has added a new DisplayPort bandwidth management feature to enable DisplayPort tunneling to coexist with other I/O data traffic more efficiently over the USB4 link. This increased efficiency is on top of mandated support for VESA’s visually lossless Display Stream Compression (DSC) codec and VESA’s Panel Replay capability. DSC bitstream support can reduce DisplayPort transport bandwidth in excess of 67 percent without visual artifacts, while VESA’s Panel Replay capability can reduce DisplayPort tunneling packet transport bandwidth in excess of 99 percent when Panel Replay operation is taking place.

The advanced capabilities of the DisplayPort video interface are enabled by the invaluable contributions by more than 300 VESA member companies from across the electronics ecosystem.

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