Apr 2

On MHL and HDMI: How Do VEE and DPO Fit?

QuickLogic’s new ArcticLink III VX devices, revealed last December, features LVDS, MIPI, and RGB interfaces.  Combined with our legacy ArcticLink II VX products with MDDI and RGB, we think we’ve got the interface needs of tablet and smartphone OEMs locked up for the foreseeable future.

When we say this, people do ask us: why not MHL and HDMI?  Even though this was asked and answered during a recent Ask the CEO blog from our very own commander-in-chief Andy Pease, I suppose we should go more into detail to eliminate any confusion and/or concern.

To answer “why not MHL and HDMI“ in plain language: because MHL and HDMI are external interfaces, and VEE and DPO don’t work that way.

First, what is MHL?  MHL is a standard started in 2008 by a consortium of Sony, Samsung, Nokia, Toshiba, and Silicon Image.  It deals with external displays being supported by mobile phones and tablets.  Simply put, MHL is an technology that allows HDMI audio and video to be passed over a micro-USB connector.  The micro-connector is form-factor friendly to even the thinnest of mobile phones; you can see a bit more detail here:


HDMI, of course, is a standard most folks have a passing familiarity to, especially in the TV world.  We all know it as the single cable that carries audio and video, replacing the alternative composite solutions of 5 separate cables (or more).

Now, to understand why MHL and HDMI are not part of the ArcticLink III VX, we need to first look at the intended use of the product.  First and foremost,  QuickLogic’s VEE and DPO technologies are designed to support embedded displays and pico projectors.  This can be seen in the block diagrams of our parts.  With embedded displays and pico projectors, system characteristics are always a known commodity.  By this, what I mean is that individual components and their performance is always the same from phone to phone (within the same model, of course).  VEE and DPO rely on design consistency to maintain the best performance.  During the system design phase, QuickLogic engages in a calibration process with the OEM, with the inputs being the OEMs desire for power savings/viewability/mixture of both, and the output being calibration curves for VEE strength and display brightness.   This calibration process may be done a few times to zero in on exactly what the OEM is looking for, but at the end of the entire development a single calibration is created that is used for the entire production of the particular phone/tablet/pico projector.

Now, a single calibration curve works very well within the production of the same device.  However, the curve for smartphone “A” might not be good for tablet “B”.  Why?

Well, smartphone A might have a display that is of much higher of lower quality than tablet B.   VEE, if applied too strongly, can actually produce less-than-desirable results—like just about anything else, too much can be a bad thing.  The same can be held true for ambient light sensors (ALS)—not all ALS’s are as sensitive as others.  If our ArcticLink device is calibrated for the high-sensitivity ALS in smartphone A, the low-sensitivity ALS in  tablet B likely will result in a display brightness curve that is well lower than needed, with VEE strength not nearly what is needed.

So let’s apply that lesson to MHL and HDMI: with a non-native display, we have NO idea what the characteristics of the display are.    While most of the time I’d wager the external display is ‘better’ (higher dynamic range and contrast, more vivid colors, etc…), that cannot always be assumed, thus making it impossible to calibrate.  In reality, even using a generic calibration is impossible.   Additionally, for best operation, VEE relies on current and accurate ambient light data as part of its process.  While some external displays do have embedded ambient light sensors, there is no way for that data to be transmitted back from the external display to the host system either over MHL or HDMI.  Accordingly, VEE would not know what the true ambient light environment is facing the user, and could over or under-compensate, giving a less-than-ideal user experience.    Further, with an non-native display, DPO could not be used, as there is no direct way for our ArcticLink devices to control brightness in today’s ecosystem.

If the MHL and/or HDMI standard evolves to encompass brightness control and ambient light levels in a send/receive architecture, then there certainly may be a play for VEE and DPO.  For now, we continue to concentrate on the embedded display/pico projector handheld market.

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