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Fine Tuning

IC chips bring digital quality to conventional radios



ALICIA CALLE
On long road trips, it's frustrating to have your favorite Coltrane jam or Mozart suite begin to crackle and fade away--or worse, to hear Pink apparently singing harmony with Pink Floyd. Weak, intermittent radio reception and interfering channels are familiar banes for motorists, but Motorola says it has an alternative to hitting the tuner's "seek" button yet again, one that can lock onto and pull in a station even when it's more noise than signal.

The engineers at Motorola's Semiconductor Products Sector in Austin, Tex., have developed a set of silicon chips that apply sophisticated digital processing to standard analog signals, enabling software code rather than analog circuitry to do the tuning, explains Steven R. Tremmel, operations manager for digital radio and digital audio at Motorola. Called Symphony Digital Radio, the system relies on algorithms running at the rate of 1,500 million instructions per second on Symphony's 24-bit semiconductor chip set. The device converts any incoming AM or FM signal into an intermediate frequency that can be filtered and conditioned by digital signal processors. The result can be near-CD-quality sound from analog radios, given a sufficiently strong signal.

The Motorola system represents an early example of a new class of what the electronics industry calls software or software-defined radios, a technology that derives tremendous flexibility by using digital code in place of fixed hardware to accomplish functional tasks. This algorithmic approach to radio was originally applied to military communications systems.

Tremmel says that the programmable aspect of the design means that both low- and high-end radio models can share substantially the same chips from the Symphony family. Manufacturers will be able to distinguish their products based on the kind of software they load into the chips. They might install, for instance, movie-soundtrack-decoding functions (such as Dolby or dts), spatial soundfield or bass enhancers, or the capability to work with various peripheral devices. Consumers may also be able to upgrade the software features after purchase.

One of the most interesting attributes of Symphony is its ability to improve reception on the road. It can essentially eliminate multipath distortion, the biggest problem for mobile systems. Radio signals can reach cars along many pathways. One path is a direct line from the antenna, but other transmissions might reflect off nearby buildings or mountains. Often the reflected signals interfere with the direct one, causing annoying clicks and pops as one drives along. When the Symphony radio is configured for dual antennas (as some luxury autos have installed in them), the chip set combines the two signals in a way that minimizes multipath distortion, says Motorola systems manager Jeremy Ho.

The system can also reduce so-called adjacent-channel interference--noise coming from a neighboring frequency. The Symphony chip set can lock onto the desired frequency even if the noise is 11 decibels louder. Its software automatically adjusts the size of its band filter to suppress nearby transmissions and isolate the target signal.

A key aspect of Symphony, however, is that it will not significantly boost the cost of car radios, Motorola insists. The company expects to earn its profit by selling makers a larger fraction of the internal workings of each radio set. South Korea's Hyundai Autonet has announced that it will incorporate the technology into its automotive sound systems, and Motorola says that other firms have signed on to purchase them as well. The technology is expected to appear in premium car radios by December 2003--so on your next long holiday drive to visit the relatives, you might actually hear Dark Side of the Moon in its entirety this time.

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