Yesterday, the MHL Consortium announced its newest flavor of display interface – Super MHL (or, more accurately, superMHL). MHL, which stands for Mobile High-definition Link, was original developed to enable display connections over Micro USB ports on phones and tablets. You’ll find it most often on mobile devices and televisions from Samsung and Sony. It will also pop up on LG products and there’s even an MHL port on the Pioneer AV receiver I bought a couple of months ago.
There have been some clever demos of MHL applications at past CES events. One was to build a “dumb” laptop (no CPU or video card) – just keyboard, touchpad, and display – and use MHL to dock a smartphone into it make everything work. Another demo in the Silicon Image booth featured smartphones being used as video game controllers with the video playing back on the controller screen.
Yet another demo showed a Sony Experia phone being used as a remote control with a Samsung TV to select inputs, play video, and launch Internet applications. It’s easy to do this stuff when you can multiplex video and serial data through the same connector, which in MHL version 3.0 can even play back Ultra HD video at 30 fps with 8-bit color.
Note the emphasis on the “mobile” part. In the world of transition-minimized differential signaling (TMDS), MHL is one of a few players, the others being HDMI (the dominant digital display interface), its predecessor DVI (still going strong although the standard isn’t updated anymore), and Micro and Mini HDMI, niche connectors on smartphones and cameras.
The advent of Ultra HD, 4K, and higher display resolutions like the new “5K” widescreen workstation monitors use has created a problem: Our display interfaces need to get faster. A LOT faster!
But HDMI 2.0, announced in September 2013, isn’t fast enough. I get into frequent debates with people about why it isn’t, so let me clarify my position: HDMI 2.0 has a maximum overall clock (data) rate of 18 gigabits per second (18 Gb/s). 80% of that can be used to carry display signals; the rest is overhead using 8 bit/10 bit mapping.
So that limits HDMI 2.0 to supporting 3840×2160 pixels (4400×2250 pixels with blanking) in an RGB signal format @ 60 Hz refresh. That’s the hard, fast speed limit. For anyone using a computer workstation or media player with RGB output, this hard, fast limit is a serious obstacle: How will people who buy the new HP/Dell 27-inch workstation monitors connect them? Their working resolution is 5120×2880 pixels, and at 60 Hz, that’s just too fast for HDMI 2.0.
It looked like DisplayPort 1.2 would finally ascend to the top of the podium, since its existing speed of 21.6 Gb/s (17.28 Gb/s usable) was already faster than HDMI 2.0. And now, DisplayPort 1.3 has been announced, with a top speed of 32 Gb/s (about 26 Gb/s usable) and the adoption of Display Stream compression. Indeed, more computer manufacturers are providing DP connections on laptops: Lenovo seems to have moved completely to this format, and Apple has been supporting DP for some time now.
With all of that in mind, I will admit I was completely blind-sided by superMHL at this year’s International CES. Instead of a 5-pin Micro USB connector, superMHL offers a 32-pin, full-size connector that’s symmetrical (the next big thing in connectivity, a la USB Type-C). It also supports Display Stream compression. And it’s compatible with USB Type-C, although not with all six lanes. And it has a maximum data rate of 36 Gb/s across six lanes of data. (According to the MHL Consortium, that’s fast enough to transport an 8K (7680×4320) image with 120 Hz refresh and 4:2:0 color.)
The MHL Consortium’s announcement yesterday featured Silicon Image’s new Sil97798 port processor, which can also handle HDMI 2.0 signals. Here are the key specs from the Super MHL press release:
Whew! That’s quite a jump up from MHL. Some might say that superMHL is on steroids, but no matter how you look at it, superMHL is now a serious contender for the next generation of display connectivity. In the press briefing, a representative of the MHL Consortium waxed on about the approach of 8K broadcasting (it’s already been operating for two years in Japan) and how we would see a migration to 8K TV and displays in the near future.
As Larry David says, “Curb your enthusiasm!” Supporting 8K would be nice, but we’ve barely started the transition to UHDTV. And right now, selling 8K TV to the average consumer is like trying to peddle a Ferrari to someone who lives on a dirt road.
Where superMHL will find its niche is in supporting the higher bit rates that high dynamic range (HDR), wide color gamuts (BT.2020), and higher frame rates (60/96/100/120 Hz) require. All will shortly become important parts of the next-generation (UHD) television system. DisplayPort is already there with version 1.3, and you’ll even find DP 1.2 connections on selected models of Ultra HDTVs so that gamers can connect laptops and desktops at Ultra HD resolutions with 60 Hz refresh.
Now, the elephant in the room: How does the emergence of superMHL affect HDMI? Even though version 2.0 is over a year and a half old, you don’t see many HDMI 2.0 jacks on Ultra HDTVs. Casual inspections at Best Buy, HH Gregg, and other outlets show that the typical HDMI 2.0 port count is usually one (1), even as we approach April of 2015.
In the superMHL presentation, the concept of a TV with multiple HDMI 2.0 inputs and one superMHL input was outlined. This would, in effect, be the next step up from where we are now, with the typical Ultra HDTV having one HDMI 2.0 input and three HDMI 1.4 inputs.
But if Silicon Image’s new Sil9779 port processor can handle both formats, why bother with HDMI 2.0 in the first place, especially with its speed limitations? Wouldn’t it make more sense to future-proof all inputs and go with superMHL across the board? (Of course, the cost of adopting superMHL could weigh heavy on that decision.)
In the commercial AV and broadcast worlds, it would definitely make sense to jump to superMHL in the interests of future-proofing installations. Given the limited rollout of HDMI 2.0 to date, maybe supporting both HDMI 1.4 for legacy devices and superMHL is a smarter approach. (Note that superMHL and HDMI 2.0 both support HDCP 2.2, which is the next level in encryption and NOT compatible with older versions of HDMI.)
Summing up; the race for faster interface speed just got a lot more interesting with the addition of superMHL to the lineup. I can imagine that manufacturers of AV matrix switchers and distribution amplifiers are feeling another migraine headache coming on…
EDITOR’S NOTE: Last week, it was announced that Silicon Image has been acquired by Lattice Semiconductor of Hillsboro, Oregon, “ a leading provider of programmable connectivity solutions” according to the press release. The acquisition price was about $600M and now leaves Lattice in control of HDMI, MHL and superMHL, and SiBEAM (WiHD) patents and IP. More information can be found on the Lattice Web site at http://www.latticesemi.com/.
Posted by Pete Putman, March 17, 2015 9:38 AM
About Pete PutmanPeter Putman is the president of ROAM Consulting L.L.C. His company provides training, marketing communications, and product testing/development services to manufacturers, dealers, and end-users of displays, display interfaces, and related products.
Pete edits and publishes HDTVexpert.com, a Web blog focused on digital TV, HDTV, and display technologies. He is also a columnist for Pro AV magazine, the leading trade publication for commercial AV systems integrators.