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Image sensor enables higher-quality images, video recording in camera phones

Posted: 04 May 2006 ?? ?Print Version ?Bookmark and Share

Keywords:ADCC-4050? image sensor? Avago? Gina Roos?

ADCC-4050 image sensor

Avago Technologies unveiled a one-quarter-inch optical format, 2Mpixel CMOS image sensor with autofocus support that enables ultra-thin camera phones to record high-definition videos (800 x 600 pixels) at 30fps and produce digital still camera-like images. It also incorporates Avago's multiplexed enhanced-performance (EP) pixels that offer several benefits including improved sensitivity in low-light conditions.

Housed in a SoC package that is comprised of the sensor, image processor and JPEG compression engine, the ADCC-4050 is one of the few 2Mpixel sensors with 2.2 x 2.2m pixels that fits into 8-by-8-by-5mm low-profile camera modules. The camera chip also combines Avago's EP pixel and array architecture and eighth generation image-pipe processing technology to achieve low image lag.

In addition, the imager's on-chip image processing and JPEG compression eliminates the need for an additional companion chip while reducing system processing overhead, design complexity, and time to market, said the company. The key improvement in the sensor array is the reduced pixel pitch from 2.8m to 2.2m, said Sanjeev Chandrasekhar, product line manager for the mobile imaging business at Avago Technologies.

To compensate for the smaller pixel, which impacts light capture, Avago developed some patent-pending changes, namely the multiplexed EP pixel architecture to ensure higher sensitivity. While the multiplexed EP pixels still use four transistors as in the earlier non-multiplexed version it allows the fourth transistor to be shared across three to four pixels. This design change translates into smaller die, increased fill factor, lower power consumption, less heat generation and ultimately, improved sensitivity and imaging.

"What we've done is to reduce the size of the pixel while at the same time increasing the fill factor and almost retaining the same ability to capture light. This also reduces power consumption and reduces the heat generated for lower noise," said Chandrasekhar.

The key benefits of the EP architecture include a reduction in dark current and noise, and the removal of the lens shading effect to offer performance that rivals CCD sensors. The 3D pixel e-field shaping is said to make each pixel ultra-light sensitive and the 8 x 8 pixel binning extends pixel sensitivity. By comparison, competitors' image sensors offer 1 x 2 binning, said the company.

The ADCC-4050 sensor is capable of 15fps at full 1,600 x 1,200 pixel UXGA resolution, and 30fps in 800 x 600 pixel SVGA mode. The image sensor contains several digital still camera- and camcorder-like image-processing features, including the eighth-generation JPEG with adaptive compression, which is said to deliver better quality images, along with advanced features such as auto thumbnails for reduced image lag and lower power use, fast reload to avoid missing shots, and spot metering with auto focus and exposure to improve captured image quality.

The image sensor also incorporates two key features for camera module assemblers. These include bad cluster correction that improves both picture quality (for users) and increases yield (for manufacturers), and color variance correction to improve camera module yields and to increase part-to-part camera module color consistency.

"The idea is to make sure there is very little color difference or performance variations from part to part," said Chandrasekhar.

The 2Mpixel image sensor also features dual flash support, shutter lag amelioration, an advanced auto illuminant detector, adaptive tone mapping for better contrast (more vivid colors), and white balance and color adjustment. In addition, the image sensor automatically adapts to a wide range of lighting conditions, from incandescent to fluorescent to sunlight, and corrects overexposed or underexposed images. The ADCC-4050 CMOS camera-on-a-chip is priced at less than $5 in quantities of 1 million. Samples are available now with volume production planned for third quarter 2006.

- Gina Roos

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