Of the 13 different silicon variants of the ArcticLink III VX devices, the one that gets the most questions is the VX3B2F, or the MIPI 2-lane to MIPI 4-lane bridge with VEE and DPO. In particular, we are asked ‘why would a customer need this?’ Here’s why:
Often in the smartphone market, OEMs ramp to bigger, better things faster than suppliers anticipate. One of those things has been display resolutions. A year ago, FWVGA (854 x 480) displays were commonplace—today, 720p (1280 x 720) have become mainstream quickly. And, as per norm in smartphones, these are mostly MIPI displays. Here’s the problem though—while 720p can be supported with 2 lane MIPI, you have to run the MIPI clock speed in excess of 800Mbps per lane to achieve this. This speed requires a lot of power, and in particular requires DDIC’s (Display Driver Integrated Circuits) to be fabricated on more modern process nodes so that they can handle those speeds. As DDIC’s tend to lag the process node curve, only the more expensive ones are on nodes capable of handling such speeds. As such, most commonly-available 720p smartphone displays will have DDIC’s that only support 4-lane MIPI, which can support 720p at much-lower, much more older-process-node-friendly speeds. This leads to a situation where the market has today is a lot of MIPI-4 720p displays, and (comparably) very few, more costly MIPI-2 720p displays.
At this point, you’re asking yourself ‘big deal, what does that matter?’
Well, it matters when processors may only support MIPI 2-lane interfaces, and NOT MIPI 4-lane. Processor vendors, whose time-to-market is significantly longer than display companies, don’t necessarily have a whole arsenal of products supporting MIPI-4. For instance, the nVidia Tegra 3, a mainstream processor, only supports MIPI 2-lane. The same is true for some Qualcomm processors purposed for the extremely-cost sensitive OEMs. Certainly the next generation of processors will likely all support MIPI 4-lane at minimum, but what about today?
There are two ways customers do this:
(A) Use the secondary RGB output of the processor (most have this output as well) and then use a RGB to MIPI display bridge. QuickLogic can offer a bridge like this, as can others.
(B) Move to the more expensive MIPI 2-lane displays in order to readily support 720p.
Option A seems like a pretty good and easy solution, at least on its face. However, the RGB output from a processor requires a much greater amount of PCB routing compared to MIPI, which is tough to manage on already heavily space-constrained smartphone PCBs. Additionally, this can add to PCB cost. Also to note is that the secondary RGB processor output is typically used today for external HDMI encoders. So, using option A may solve the problem, but does potentially create design and usability concerns as a side effect.
Option B, well…we covered it earlier. An OEM who chooses this route adds BOM cost and ties themselves to a much smaller supply base.
QuickLogic can offer a third way, one we believe is better than the two above:
(C) Use the ArcticLink III VX3B2F, a single chip solution that bridges MIPI 2-lane to MIPI 4-lane, allowing OEMs to use the less-expensive, more readily available MIPI 4-lane displays with their existing processors MIPI 2-lane output.
The VX3B2F accepts a MIPI 2-lane interface from the processor at up to 1Gbps (well in excess of speeds needed to support 720p). From there, our VEE and DPO technologies (and even IBC) adopt the display content for best viewability and power savings. Once VEE is done (a matter of microseconds), the 2-lane MIPI signal is then bridged to a 4-lane MIPI signal, which in turn is then outputted to the display. While the 4-lane MIPI output of the VX3B2F is a lower speed per lane, the total amount of data passing through is equal to the MIPI 2-lane output of the processor. This allows OEMs to realize the marketing and user value of a 720p display without the added cost and potential security of supply issues of a 2-lane MIPI display. Additionally, the PCB routing needs are much lower compared to using RGB, which can lead to lower costs.
Sounds like a winning proposition to me.