With the recent rise of popularity of adding MHL or HDMI interfaces to tablets, already-overburdened system designs now face another challenge—how to integrate a secondary video output into a system designed to support only the on-board display?
This is a huge challenge, primarily so based on (1) the number of concurrent outputs that CPU’s generally support and (2) the interface support required.
Let’s talk about the simultaneous output issue first. As many eagle-eyed readers know, most mobile-centric CPUs support MIPI. Some also offer additional support for RGB natively, but not all of those offer concurrent support for both interfaces simultaneously. Meaning, the MIPI interface can be used, or the RGB – not both at the same time. Additionally, while some mobile-centric processors support native HDMI, very few actually support a native MHL output. MHL is typically supported by integrating a 3rd party device dedicated just for MHL.
This presents an issue, given that a system with MHL/HDMI is going to require two separate, distinct, and concurrent video data flows from the processor. MIPI and RGB data cannot readily be ‘multiplied’, meaning there is no practical market-appropriate way we know of to take a single MIPI or RGB data flow and duplicate it real-time.
Secondarily, the interface support required can be a challenge. For instance, we’ve mentioned MIPI on processors as being pretty much standard. Additionally, it’s well known that tablet displays are most often LVDS. The current accepted solution for supporting MHL lies in devices that push MHL to external displays from an RGB signal from the host. Ultimately, the MIPI signal from the CPU has to be converted to LVDS for the embedded display, and RGB for MHL support.
So, without mass-market processor support for two outputs (of varying interfaces) and varied native MHL/HDMI support from processor, where does the system designer turn?
QuickLogic’s ArcticLink III VX6 CSSP series
The tablet-friendly VX6BxG, which accepts MIPI from the processor, bridges LVDS for the embedded display (after applying VEE and DPO technologies), as well as a non-VEE and DPO-applied RGB signal to the MHL transmitter. This solution only requires the single MIPI output from the processor, with all timing signals and interface bridging handled on the VX6 device.
A couple of other answers to questions that you might have:
- We don’t apply VEE and DPO to the RGB signal – this is because we don’t have ambient light information provided to us by the external display. I blogged about this almost a year ago at http://quicklogic.wpengine.com/display/on-mhl-and-hdmi-how-does-vee-and-dpo-fit/
- Yes, these are available in BX (non-VEE and DPO) silicon variants as well, pin-identical as always
The ArcticLink III VX6 series are mass production-ready and available for evaluation now. If you are interested in getting more information on the devices, please fill out the form below and we will be in touch with you.
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Paul,
Reading your blog entry, and thinking ahead to embedded Picoprojectors, it seems to me that a version of BX III and VX III that supports three simultaneous video outs might be a future market need. Is this practical, or am I missing something in my thinking?
Hello Dennis,
Thanks for reading, and for the question.
Certainly a three output device is something that might be needed in the future, with the possibility of device with an embedded display, external display, and embedded pico projector. This type of architecture would present two immediate challenges–the first is which interfaces to support (LVDS, RGB or MIPI) and in what arrangement, as RGB is likely needed for the both external display and embedded pico; the second is the amount of connections needed on the actual packaged silicon device. Our current ArcticLink III device is 4.5 x 4.5mm with 120 balls (interconnects to the board it is attached to). We would need to add more balls for a third interface, which runs the risk of making the package larger (not a good thing in the smartphone/tablet world) or more expensive (ditto).
All in all though, very good observation, and certainly not the first time this idea has been discussed.
Paul
Thanks Paul for the prompt reply.
Regarding the first challenge,the market ought to reveal that to you over the coming year, and the second challenge might be worth it if the market is large enough, and you have the only such device for that market.
But, maybe you can avoid both problems because you already have 4 dual output variants, I believe. By simply using two dual output BX or VX devices in serial, it should allow for 3 outputs and multiple input/output combinations. Is that feasible?
Dennis,
But, maybe you can avoid both problems because you already have 4 dual output variants, I believe. By simply using two dual output BX or VX devices in serial, it should allow for 3 outputs and multiple input/output combinations. Is that feasible?
100% technically feasible.
Paul
Paul,
I’ve thought a little more about the three video output possibility in future mobile devices using two BX or VX parts, and I have a couple of other questions. If you ever did this for a customer, depending on the combination of BX and/or VX devices used, and standard MIPI input in all cases, I see six possible output combinations, which could result in both straight digital RGB out (BX) and “VEE enhanced” (VX) digital RGB out.
My questions are that I can see that pico projectors would need “VEE enhanced” RGB out (with BCC etc), but would MHL out to TVs or monitors use just BX RGB, or is there any possible improvement to the pictures displayed on HD TVs from a mobile device, by sending a “VEE enhanced” output to it?
I’m also thinking of possible future outdoor viewing of devices that might be wired instead of battery powered. I mean, besides signs, there are times TVs and monitors are used outdoors, and perhaps also receiving streaming video from a mobile device. Can VX improve an outdoor TV or monitor picture? I know TVs and monitors have much higher contrast, but would outdoor viewing be improved with VX and an ALS (to adjust for sunny vs cloudy, etc.)?
Hey Dennis,
While the possibility exists that we could improve viewability of external display with VEE and DPO, unfortunately the ecosystem does not exist to allow us to do so. In the blog at http://quicklogic.wpengine.com/display/on-mhl-and-hdmi-how-does-vee-and-dpo-fit/, I talk about a number of reasons why this is difficult; different calibration curves, lack of brightness control of external displays, and the fact there is no way to receive ambient light information of external displays over existing MHL/HDMI interfaces.
Thanks!
Paul
Paul-
Should we expect to see AP companies include LVDS LCD interfaces in their tablet-centric processors or is there a technical/cost reason for them to use MIPI?
Thanks,
Brian
Brian,
Yes, you should expect to see this for some tablet-centric processors.
Paul