Cirrus Logic Inc. introduced an analog front-end interface chip (CS7620) that provides superior image quality and design flexibility for charge-coupled device (CCD) digital still cameras. Designed in conjunction with Polaroid Corporation and IBM, the new Crystal Digital Imaging chip provides all of the critical functions necessary to bridge the gap between the CCD and back-end still-camera processor.

The CS7620 is especially suited to the emerging digital still camera market, which, according to a recent Semico Research Report, is expected to reach 6 million units in 1999 growing to 26 million units in 2002. Using Cirrus Logic's DRX technology to provide up to 13-bits of intra-scene dynamic range, the CS7620 can improve image clarity and details as well as reduce system cost and increase camera performance. Cirrus Logic expects its chip to move into volume production during the second calendar quarter of 1999.

Flexible, Highly-Integrated Solution
The CS7620 integrates all of the critical functions required to interface with a variety of CCDs: a correlated double sampler (CDS) for superior image quality; a DRX enabled analog-to- digital converter (ADC) for variable resolution images; a flexible on-chip timing generator; and two programmable digital-to-analog converters (DACs). For the popular megapixel CCDs, the on-chip- timing generator can be used to drive the CCD in snapshot mode (still picture) and in preview mode (low-resolution video). A partial-master mode and slave mode can be used for CCDs that require a different timing generator for vertical, or vertical and horizontal timing, respectively. In addition, the CS7620 supports a wide range of CCD saturation voltages by providing programmable full-scale input range. And because the CS7620 integrates programmable DACs for substrate bias control, it reduces system chip count and thus total system cost.

To minimize power consumption in the battery-operated mode, the CS7620 offers a low- power, low-resolution preview mode that significantly reduces the chip power when previewing video on the camera's built-in LCD panel.

Designed With the Camera in Mind
"We worked with both Polaroid Corporation and IBM, the manufacturers of Polaroid's CCD designs, to optimize the performance of our Crystal image processing chip with the CCD in a system environment," said Douglas Holberg, director of Crystal Imaging and Video Products at Cirrus Logic. "In designing the CS7620, we carefully evaluated the complete camera system design. By working closely with the CCD designers at Polaroid, we were able to address the fundamental noise performance of CCDs, allowing us to optimize the analog signal path to maximize dynamic range thus enhancing picture quality."

"We found that the Crystal Imaging team from Cirrus Logic was able to take our image capture expertise and apply their mixed-signal skills to create an optimal analog signal processing solution," said Dr. Stuart Spitzer, director of Image Sensor Technology Division of Polaroid Corporation.

"The mixed-signal Crystal team at Cirrus Logic worked very closely with us to make sure that their image processing chip fit tightly with the CCDs we are bringing to market," said Ken Torino, director of IBM Microelectronics Semiconductor Contract Manufacturing Services. "In addition, we co-developed an evaluation platform that demonstrates the performance of our CCDs operating with the CS7620. By working together, we can enable manufacturers to reduce production costs and improve time-to-market, placing digital still camera products within reach of more consumers."

Although the last sentence -- and a number of the features offered -- allows for the possibility of using the CS7620 with any variety of CCD source, the product was clearly developed to enhance the output of the IBM products that have been developed from Polaroid designs. The completion of development of the product is a tacit blow to the analog semiconductor producers of AFEs for CCD systems whose products are used in scanners. Many assumed that they would be the first source for the emerging digital still cameras. Few people, it seems, understand the limitations of 8- and 10-bit (but processed at 8 bits) resolutions if they were to br used for a still "photographic" image. Dynamic range capabilities in photography are considerably greater than those of a video channel. The 13-bit, full-resolution, processing with this part will allow those dynamic ranges to be produced. It will be a considerable time before software applications for a PC platform will follow suit, but they must come to allow for desktop manipulation of the images.

Working so tightly with Polaroid and IBM gives the Crystal division at Cirrus a major heads-up in this market and it doesn't seem to be compromising the features provided. The now-standard CDS is employed and the arrangements allow for the full signal range of the ADC to be used. The use of feedback DACs for substrate bias correction is not the normal architecture that most AFE vendors are employing but neither is it a novel design approach. This will be a major money-maker for Cirrus.