CMOS sensors strive for CCD-like success

-- EDN, 12/7/2000

It's been three years since EDN last examined CMOS sensors, and the news since then hasn't exactly been earth-shattering (see "CMOS image sensors: eclipsing CCDs in visual information?" EDN, Oct 9, 1997, pg 101). Resolutions for high-performance production-worthy CMOS sensors remain stuck at or below 1 million pixels, and both light-sensitivity improvements and pixel-noise reductions are slow in coming. Meanwhile, less-than-$1000 digital cameras containing CCDs with more than 3 million-pixel resolution are rapidly disappearing from store shelves; that price three years ago got you a 1 million-pixel, lower quality CCD-based camera. CMOS sensors aredelivering on their promise, though, in their cost-reduction potential, thanks to a high degree of process compatibility with standard CMOS logic.

Take IC Media, for example. Thanks to its use of UMC's 0.35-µm procss, IC Media's ICM105A 640×480-pixel (VGA resolution) CMOS sensor costs $7.35 (10,000) (Picture). Small pixel dimensions, at 6 µm per side, translate to smaller—3.8×2 mm, in this case—sensors than similar-resolution sensors built on less advanced proesses. This silicon reduction cuts the camera cost not only by making the sensor more economical, but also by making the optic system required to achieve a specific focal length smaller and cheaper. The ICM105A provides an 8-bit output (driven by a 9-bit ADC) and I²C system interface and includes both automatic black-level calibration and a correlated double-sampler for noise reduction. Light sensitivity is 2.5V/lux-sec (7V/lux-sec upon application of transfer gate gain), and typical power consumption is 30 mA at 30 frames/sec and 3.3V and with a 27-MHz clock. Now in production, the sensor comes in 48-pin CLCC and PLCC packages.

Agilent Technologies is resurrecting its more-than-two-year-old, $7.95 (10,000), 352×288-pixel (CIF resolution) HDCS-1020 and $12.25, 640×480-pixel HDCS-2020 CMOS sensors. The company first introduced these sensors when it was a division of Hewlett-Packard. Agilent now makes them on a more advanced process capable of 7.4-µm-per-side pixel dimensions with a 40% fill factor. Agilent rates the 3.3V HDCS-2020, which includes a 10-bit ADC and 10-bit output, at 15 frames/sec, whereas the smaller HDCS-1020 includes an 8-bit ADC and can hit 30-frame/sec performance. Both sensors come in 32-lead PLCC packages.

For its reference designs, IC Media has partnered with image-processor companies, such as Ark Logic, Crescentec, EndPoints, and Philips. Agilent, on the other hand, provides both sensors and image processors, as well as associated reference boards and their documentation, optics, scheatics, and software. The $7.95 (10,000) HDCP-2000 targets low-cost, motion- JPEG-based, USB videocameras. It's well-matched to its companion sensors, can exceed 15-frame/sec processing speeds at VGA resolution and 30 frames/sec at CIF resolution, comes in a 64-pin PQFP, and requires no external frame buffer.

The HDCP-2010, a close cousin of the HDCP-2000 but in a 44-bump µBGA package, replaces the USB controller with a generic serial or 8-bit parallel interface that can output either JPEG or 4:2:2 YUV formats; it targets systems with embedded-camera functions, such as portable computers and cellular phones. The top-of-the-line $17 (10,000) HDCP-3200, intended for dual-mode digital still cameras, supports JPEG compression and decompression, offers numerous external-interface options, and handles both image- and control-processing functions, courtesy of an embedded 32-bit, 144-MHz Motorola ColdFire 3M core. It comes in a 208-pin PBGA package. All three processors operate at 3.3 and 1.8V and are, along with the sensors, in production.

Predictions of future CMOS-sensor success remain bullish. Cahners In-Stat, for example, claimed in a recent report that, by 2004, 50.8% of all image sensors would be CMOS versus 7.2% last year. Even the most optimistic CMOS advocates admit, though, that CCDs will for the foreseeable future still be the sensor technology of choice for ultrawide-dynamic-range and ultrahigh-resolution applications. Kodak, for example, recently announced the $4000 (1000), 16.6 million (4080×4080)-pixel KAF-16801CE CCD. But even Kodak's hedging its bets. The company also recently introduced the $11 (10,000), VGA-resolution KAC-0310 CMOS sensor, now in production, and the 1 million-pixel-resolution KAC-1310 CMOS sensor will follow by year-end.

Agilent Technologies, 1-650-857-1501, www.agilent.com.

IC Media, 1-408-451-8838, www.ic-media.com.

Kodak, 1-716-724-4000, www.kodak.com.

—by Brian Dipert