The Omnivision OV5610 5.17-Mpixel camera chip packs a similar-sized pixel array and an on-chip ADC (10 bits versus Micron's 12 bits). But like the Kodak chip, it uses a 1/1.8-in. optical format and similar-sized pixels. It's the slowest of the three, though, delivering 4 full-resolution frames/s. On-chip circuitry and algorithms cancel fixed-pattern noise, eliminate smearing, and drastically reduce blooming and dark current. And, it can perform optical black-level calibration to achieve a 60-dB dynamic range comparable to the Micron sensor.
Active power consumption is about 140 mW while standby current is below 35 µW, suiting the chip for standalone cameras and camera phones. Control registers let designers manipulate the timing, polarity, and chip functions such as programmable auto-exposure, gain control, and auto white balance.
Planet82's approach uses a scheme the company calls single-carrier modulation photo detectors (SMPD). This technology creates an image sensor that functions like an artificial eye, capturing images without a flash in almost total darkness. The pixel element is based on a quantum transistor structure rather than a PN diode, and it has a sensitivity more than three orders of magnitude higher than CMOS or CCD-based sensors.
It can capture pictures without a flash—even with light levels below 1 lux, which is better than what the human eye can distinguish. The scheme also minimizes the aperture ratio of the pixel region, allowing more pixels per unit area on the chip. This shrinks the size of the chip compared to CMOS sensors using the same design rules. Power consumption also will be lower, typically about 82 mW for the 5-Mpixel sensor. Planet82 expects to start sampling the sensors in mid-2006.
As resolution drops to 3 Mpixels and below, more vendors now compete at today's sweet spots of 3- and 1-Mpixel resolution. Cypress Semiconductor, Kodak, Magnachip, Micron, Omnivision, and Toshiba join the fray at the 3-Mpixel level. Avago Technologies (formerly Agilent), Sharp, and STMicroelectronics can be found at 2 Mpixels and below too.
SENSORS TAKE DIFFERENT PATHS
Vendors in this market are moving in two directions. On the one hand, they design basic sensors with minimal on-chip logic. On the other, they're creating highly integrated camera-on-a-chip solutions with functions such as JPEG image processors, autofocus control, flash strobe control, and other image and video support functions. These approaches let cell-phone designers better match their phone architectures to the imaging subsystem. In addition to offering bare sensors, the vendors can offer value-added modules that combine the sensor, a fixed or variable-focus lens, and some control logic. (For more, see "Module Or Discrete" at www.elecdesign.com, Drill Deeper 11881.)
At 3 Mpixels, most imaging chips don't include high-level processing functions. But they usually can offer higher frame rates than larger sensor arrays. For instance, Micron's MT9T012 leverages the same 2.2-µm square pixels as the company's 5-Mpixel chip. It can deliver 15 frames/s at full resolution and up to 30 frames/s at lower resolution.
Targeting mobile applications, it uses a 1/3.2-in. optical format and includes programmable snapshot and flash control.
Kodak's KAC-3100 also leverages the 2.7-µm pixels of its larger brother, the KAC-5000. At 12 frames/s, it's twice as fast as the 5-Mpixel sensor. However, it's still slower than Micron's 3-Mpixel chip.
The ICM320T image sensor developed by Magnachip ( formerly IC Media) pushes speed a bit further. It uses 2.57-µm square pixels and a 1/2.7-in. optical format to deliver a full-resolution frame rate of 16 frames/s and progressively higher rates when the array is subsampled. The chip is frugal with power, consuming 70 mW at 15 frames/s and less than 20 µW on standby. Like the Micron sensors, a two-wire interface controls the various operating modes (exposure time, frame rate, subsampling window size, analog and digital gain, horizontal and vertical image inversion, and dead pixel removal).
Also delivering 15 frames/s, the OV3630 from Omnivision and the PS1320 from PixelPlus perform at levels similar to the Micron MT9T012. Based on a proprietary pixel structure the company calls Omnipixel2, the OV3630 sensor can cancel fixed pattern noise and considerably reduce smearing and blooming. Meanwhile, the PS1320 incorporates an on-chip image signal processor that lets users program various windows and frame rates, handle a video preview mode, and perform black-level compensation.
Toshiba's entry into the 3.2-Mpixel market, the ET8E99-AS, uses a 2.7-µm pixel and a 1/2.6-in. optical format. In its full-resolution mode, it too can deliver 15 frames/s and over 30 frames/s when pixels are binned (3-to-1 vertical binning). An on-chip ADC delivers raw digital data to the host over a serial differential interface (Fig. 2). It supplements the company's existing 2-Mpixel, 1.3-Mpixel, and VGA sensors and modules.
Designers can choose from many 2- and 1.3-Mpixel standalone sensors under the 3-Mpixel level. But these devices require external processors to take the image data and deliver JPEG still images or video. To lower system costs, a few companies are creating single-chip cameras that offer a more highly integrated solution.
Such chips include Micron's 2-Mpixel MT9D111 and 1-Mpixel MT9M111, as well as Avago's 1.3-Mpixel ADCC-3960. They include JPEG image processors and other system support logic that offload the host processor in a cell phone or camera. Thus, it becomes easier to add the camera function to an existing chip-set solution.
For a complete list of vendors, go to www.elecdesign.com, Drill Deeper 11900.