NORWOOD, Mass. — Analog Devices Inc. has developed a family of CMOS analog front ends intended to bring higher-resolution pictures and longer battery life to digital cameras and camcorders. The AD984x devices are designed to attack the Japan-dominated market in ICs for digital cameras. Japanese IC manufacturers control the lion's share of that market in part because Japan's camera makers jumped on the digital bandwagon early.
John Hussy, vice president in charge of high-speed converters at Analog Devices, estimated that between April and September of 1999, Japan-based companies consumed roughly 2.3 million units of high-speed converters. That would make the 1999 Japanese market about 4 million units, and the worldwide market roughly 12 million.
Digital cameras consist of a charge-coupled device (CCD), an analog front end (AFE) and an image processor. The AFE is considered key to low-noise, high-resolution images. The AD984x product line provides signal conditioning and data conversion for the output of the color CCD. The AD984x performs correlated double sampling, gain adjustment, black level correction and analog-to-digital conversion with a pipelined converter. The family includes two devices: the AD9840 samples at 36 MHz for digital camcorder applications and the AD9843 samples at 18 MHz for digital still cameras.
In a digital camera system, the AD984x's output data is manipulated by a digital signal processor or image-processing ASIC. The internal registers of the AD984x are used to control gain; offset level and other functions are programmed by the ASIC or microprocessor through a three-wire serial digital interface. A separate timing generator provides the clock signals for both the CCD and the AFE.
The AD9840 produces a 10-bit image and is intended for consumer cameras. The part is already shipping in Japanese-made camcorders, said Bill Murphy, product manager for ADI's high-speed converter line. The device costs $5.66 each in 1,000s.
A forthcoming member of the AD984x family, the AD9844, is a 12-bit device that supports higher image resolution and picture dynamic range. This has enough resolution to show the "Baboon's Hair" in the well-known test image produced by Sony, said Murphy.
Murphy said that "shelf tag marketing" — a camera or scanner sold according to the number of bits — is not a good indicator of image quality, which is also contingent on noise performance. The noise figure of the AD984x is 0.2 LSB (least significant bit) at minimum gain settings, or less than one part in 5,120. At maximum gain settings, the noise tends to rise to 3.75 LSB, or almost four parts in 1,024.
In addition to low noise, the AD984x features include low power consumption — as little as a third as much as competing products from Asahi Semiconductor and Burr-Brown, according to Analog Devices. The AD9843, for example, consumes a maximum of 75 milliwatts in operation. Low power consumption also means higher battery life.
"It's a thing these camera guys are maniacal about," said Murphy.
