Analog Devices Inc and Aware Inc have co-developed an alternative to the Carrieless Amplitude and Phase Modulation technology, CAP, developed by AT&T Bell Laboratories to carry analogue and digital signals over copper wire (CI No 2,656). The chip set has taken two years to develop and is the first commercial product that privately-owned Aware, Bedford, Massachusetts, has been involved in. Aware develops wavelet technology for digital image compression. Both the AT&T system and Analog Device’s AD633 use Asymetric Digital Subscriber Lines technology which splits signals so compressed films, graphic-intensive World Wide Web files and speech data can be carried over the same copper cabling. But Analog Devices claims its system, which was co-developed with Aware, has higher data transfer speeds and is less susceptible to electromagnetic interference over long distances. The AD633 chip set uses discrete Multi-Tone modulation which is claimed to have a higher tolerance to electro-magnetic interference because it breaks a data stream into individual packets and, therefore, reduces the chances of a whole signal being corrupted. The chip set has a 6Mbps downstream capacity and a 220Kbps back channel over two miles; AT&T CAP in contrast, has the same downstream speed but a back channel capacity of 64Kbps over an optimum distance of 300 feet. Analog Devices said that Bell Atlantic Corp, Nynex Corp and British Telecommunications Plc all currently use CAP but are now trying out the ADSL chip sets following the American National Standard Institute’s decision to opt for Discrete Multi-Tone Modulation over CAP as the standard for ASDL lines. The chip set has been designed in both software and silicon to make any changes easier and quicker to implement, the company said. The system uses two standard 21061 SHARC digital signal processors running at 33MHz with 1Mb of on-chip memory for the core processing functions and two dedicated signal processors to act as an interface and filter to the digital-to-analogue conversion carried out in software. However, both Aware and Analog Devices said that they will produce a hardware-only system by next summer using four processors to cut the price for each ASDL line from $450 to $300, and they believe they will be able to bring the price down to $200 by 1997.
