Motorola Symphony Digital Radio
Dec 1, 2002 12:00 PM, by Chriss Scherer, editor
The Motorola Symphony Digital Radio is a matched chipset approach todigitize the receiver section of a radio. The three-chip approach usesthe Motorola DSP56300 general-purpose 24-bit Onyx DSP core with an RFfront-end and IF analog interface. The pieces could be placed into asingle-chip package instead of three discrete ones, but keeping themseparate allows design improvements in one of the three sectionswithout affecting the other parts, requiring an entire tooling processto be redesigned.
First creating a stir at the Fall AES and NAB Radio conventions thisyear, Motorola has developed this system to improve radio reception atthe receiver by using the 1,500 MIPs processor to demodulate thereceived signal. The improvement comes without any transmission changesrequired of the broadcaster.
Figure 1. Signal flow and component structure of the SymphonyDigital Radio.
The initial stages of the radio design are familiar building blocks.Figure 1 shows the system’s block diagram. The wideband tuning and RFfront-end carry the same workload as their predecessors to provide abandwidth-limited signal to the IF stage. The bandwidth limiting isadjusted to fit the signal being received, providing the first step ineliminating unwanted noise and interference. The variable IF filteralgorithm used in this system automatically adjusts to 100kHz and200kHz band channel spacing.
Once the signal has been received, the RF front-end stage upconvertsit to 10.8MHz. This is the point where the fundamental designdifference begins.
This IF stage digitizes the RF signal before passing it to theBaseband Audio Processor. Once in this DSP stage, the signal can bedemodulated and processed with the improved accuracy that DSPoffers.
While some of the DSP structure is used for equalization and otherlistener-defined settings, the core is used to examine a signal andmore efficiently remove the effects of multipath noise andinterference. Additionally, improvements to the radio design can beimplemented without redesigning the entire radio. Updates can beprogrammed into the radio directly.
The design also lends itself to decoding new formats, such asmultichannel sound, if this is ever developed for radio. The ability todecode RBDS data is inherent to the design because of themicroprocessor control and demodulation.
To add more flexibility to the system, an optional RF section can beadded. These additional components can be used to provide a diversitytuning option, further enhancing reception. The diversity receiverdiffers from current designs in that the IF does not switch between thebetter signal at any given moment, but instead takes both signals intoaccount, creating a better signal from the two. This method provides amore robust signal to be digitized.
Another use of the second RF section is to provide a second receivedsource. The two RF sections can remain separate. One application wouldbe the ability to listen to one station in the front seat and anotherstation in the back seat.
Motorola has stated that this approach was designed for currentanalog transmissions, but there is no reason that it could not beapplied to other methods, including IBOC.
Motorola is working with several established consumer radiomanufacturers to produce receivers. Hyundai Autonet has alreadyannounced plans to build and market Symphony radios with deliveryscheduled for the end of 2003.
One more advantage to the new design is that the overall cost toproduce the radios is slightly more than the existing designs, whichshould speed acceptance of the new products because of the marginalprice increase.
Hear Motorola’s comparison of a traditional analog receiver to aSymphony receiver.