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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