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Sensor bolsters smart phone's imaging quality

Posted: 24 Dec 2009     Print Version  Bookmark and Share

Keywords:Storm BlackBerry  imaging quality phone  video image quality 

Blackberry Storm packs OV3647 low-power, low-cost CMOS image sensor from OmniVision Technologies.

The BlackBerry Storm came out not too long after I bought a Blackberry Curve. Like lots of the latest consumer electronics devices, you're always hesitant to jump in and make a purchase, because you know your device will be trumped by something cooler in a very short time.

That was the case with my Curve—but not exactly. Shortly after I acquired my Curve, the Storm crossed my desk, as the object of a Tear Down. My first inclination with a Tear Down is to try the device out for a while, to get a feel for the user experience. In this case, it was to see what I was missing out on.

To my surprise (and delight), I found out that the Storm doesn't have a better user experience. In fact, I like my Curve better. The biggest reason for that is the touch interface that accompanies the Storm. I found it quite difficult to press the right buttons. I may have big fingers, but they're not very big that I should have that much trouble with the interface.

Being the engineer that I am, I decided not to let that one design flaw completely ruin the user experience, although it was hard to get passed that point. I found that as a telephone, the Storm worked really well. And that's an important component, although I use the phone more for e-mail and texting than I do as a phone (Nobody calls anybody anymore, do they?).

The second feature I found to be quite attractive was the imaging quality, both for still images and for video. So that's where my Tear Down started. I wanted to find out what was the cause of those qualities that I found to be appealing.

Image sensor
The sensor the Blackberry Storm is from OmniVision Technologies, the OV3647. It's a low-power, low-cost CMOS image sensor. Containing a parallel interface and a mobile digital display interface (MDDI), the sensor has a resolution of 3Mpixel running at 15fps. It has embedded PLL and can be embedded into a module that's 7mm x 7mm x 5mm, as is the case in the Storm. It has an embedded 1.5V regulator for operation at full power, but the core power is about 1.4V.

OmniVision did some scripting for the Storm and tuning the image parameters so the image looks the best regardless of temperature.

The OV3647, which is related to the sensor in RIM's Blackberry Curve handset (the OV2640), supports a raw RGB output format, image sizes of QV-XGA and XGA, and has a programmable frame rate. Image quality controls like lens correction, auto exposure, auto gain, auto balance and defect pixel cancelling help enhance the images, along with support for LED and flash-strobe mode.

One of the unique features of the OV3647 is that it contains Qualcomm's proprietary MDDI. This is a key differentiator because it provides a proven solution for the interconnect challenge provided by the hinge in a flip (clamshell) phone. This reduces the wire cost and ultimately reduces the overall system cost.

According to the engineers at OmniVision, the interface also helps reduce the EMI in the differential signalling protocol. This, in turn, eliminates the need to use a parallel port where you've got eight data bits swinging at 1.8V with a clock and two syncs signals.

While the Storm obviously doesn't employ a clamshell design, the EMI is reduced nonetheless. Qualcomm supports MDDI on most of its newer chipsets. Hence, it gives OmniVision easier entry into a Qualcomm design.

While the phone was designed by RIM, the designers at OmniVision were involved in integrating the sensor into the handset. This process occurred about 18 months ago.

While it's obviously a hardware integration challenge, there were some software issues that OmniVision had to iron out with RIM, like which settings should be used. OmniVision's applications team worked hand in hand with RIM to get the best image quality, resolution etc. That led to OmniVision doing some scripting for the Storm and tuning the image parameters, like the lens correction and the defect correction, so the image looks the best regardless of temperature. The OmniVision developers also had to ensure that they provided the modes for all image sizes.

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