Motorola Symphony Digital Radio

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The Motorola Symphony Digital Radio is a matched chipset approach to digitize the receiver section of a radio. The three-chip approach uses the Motorola DSP56300 general-purpose 24-bit Onyx DSP core with an RF front-end and IF analog interface. The pieces could be placed into a single-chip package instead of three discrete ones, but keeping them separate allows design improvements in one of the three sections without affecting the other parts, requiring an entire tooling process to be redesigned.

First creating a stir at the Fall AES and NAB Radio conventions this year, Motorola has developed this system to improve radio reception at the receiver by using the 1,500 MIPs processor to demodulate the received signal. The improvement comes without any transmission changes required of the broadcaster.

Figure 1. Signal flow and component structure of the Symphony Digital Radio.

The initial stages of the radio design are familiar building blocks. Figure 1 shows the system's block diagram. The wideband tuning and RF front-end carry the same workload as their predecessors to provide a bandwidth-limited signal to the IF stage. The bandwidth limiting is adjusted to fit the signal being received, providing the first step in eliminating unwanted noise and interference. The variable IF filter algorithm used in this system automatically adjusts to 100kHz and 200kHz band channel spacing.

Once the signal has been received, the RF front-end stage upconverts it to 10.8MHz. This is the point where the fundamental design difference begins.

This IF stage digitizes the RF signal before passing it to the Baseband Audio Processor. Once in this DSP stage, the signal can be demodulated and processed with the improved accuracy that DSP offers.

While some of the DSP structure is used for equalization and other listener-defined settings, the core is used to examine a signal and more efficiently remove the effects of multipath noise and interference. Additionally, improvements to the radio design can be implemented without redesigning the entire radio. Updates can be programmed into the radio directly.

The design also lends itself to decoding new formats, such as multichannel sound, if this is ever developed for radio. The ability to decode RBDS data is inherent to the design because of the microprocessor control and demodulation.

To add more flexibility to the system, an optional RF section can be added. These additional components can be used to provide a diversity tuning option, further enhancing reception. The diversity receiver differs from current designs in that the IF does not switch between the better signal at any given moment, but instead takes both signals into account, creating a better signal from the two. This method provides a more robust signal to be digitized.

Another use of the second RF section is to provide a second received source. The two RF sections can remain separate. One application would be the ability to listen to one station in the front seat and another station in the back seat.

Motorola has stated that this approach was designed for current analog transmissions, but there is no reason that it could not be applied to other methods, including IBOC.

Motorola is working with several established consumer radio manufacturers to produce receivers. Hyundai Autonet has already announced plans to build and market Symphony radios with delivery scheduled for the end of 2003.

One more advantage to the new design is that the overall cost to produce the radios is slightly more than the existing designs, which should speed acceptance of the new products because of the marginal price increase.

Hear Motorola's comparison of a traditional analog receiver to a Symphony receiver.

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