Digital radio ready to move forward - Embedded.com

Digital radio ready to move forward

With its Symphony Digital Radio chipset Motorola is providing acomplete digital intermediate frequency (IF) radio solution. Itcombines special purpose (co-processor) digital signal processors(DSPs) and the DSP56300 general-purpose 24bit Onyx DSP core with anradio frequency (RF) front-end and IF analog interface. This provides1500 MIPs to allow consumers to receive more from the broadcastsignals.

Symphony three-chip solution for AM/FM/WB

The performance improvement is provided by software tuning of theradio instead of the traditional mechanical means. It will initiallybe used in automotive applications but should be also useful in othersystems.

Motorola says the Symphony Digital Radio can find signals that astandard radio cannot. Adjacent radio signals often interfere witheach other, not because they're just close together, but becausetraditional tuning cannot lock onto a signal and stay on through anynumber of variable circumstances, such as atmosphericinterference.

The variable IF filter algorithm used in Symphony automaticallyand dynamically adjusts itself to both 100kHz and 200kHz band channelspacing, which allows it to react to any changes.

Static and fade-out

In the car, as a driver moves further from one radio station andcloser to another, the channel frequencies can overlap, causingstatic and fade-out. Symphony's Channel Effects Equalizer minimizesthis effect, allowing travelers to 'hold' on” to a clear signallonger.

A radio signal reaches a car in a number of ways. One way is adirect line from the broadcast, but another is reflected signalsbounced off buildings or mountains. Often the reflected signalinterferes with the direct signal, causing annoying clicks and pops,also known as multipath distortion. Symphony will minimize theseeffects, allowing a station to be audible for longer.

The FM demodulator algorithm used in Motorola's Digital IF Radio,which separates the FM signal from the carrier, provides superiorrange extension and improved signal-to-noise ratio (SNR) under weaksignal conditions over traditional digital demodulation techniques.The radio should be able to pick up weaker signals from a greaterdistance with clear reception.

In addition, the Symphony Digital Radio provides good stereoseparation, often greater than 40dB. The software architecture allowsfor audio processing and radio tuning simultaneously on a singleprocessor/software thread. It can now handle dual audio streams.

New features can be written into RAM or ROM instead of waiting fornew silicon to be added, this will enable improved performancewithout enlarging the footprint. Customers can tweak radioparameters, turn various algorithms on or off for experimentation,even develop their own algorithms and software and download them intoRAM.

The baseband/audio processor also features a number of 'plug andplay' audio post processing features with available program and dataRAM for customer-supplied or customer-specified advanced audioalgorithms.

These features include volume control, dynamic range compression,parametric EQ (equalization), graphic EQ, bass/midrange/treblecontrol, loudness, speaker compensation, spectrum analysis, and leveldisplay.

Improving functionality 'on-the-fly' can cut time-to-market fornew products. This is particularly true if changes are in softwareonly because it involves simply downloading RAM code. If enhancementsare to be realized in firmware, they can be prototyped in the RAM ofthe baseband/audio processor. A new ROM mask can then be burned forproduction without requiring new qualification of silicon.

Avoiding new silicon

In traditional analog radios, new features require either asilicon redesign or additional silicon on the PC board, thusrequiring a PC board redesign and requalification. This all takesextra time and money.

The exclusively digital, soft-core nature of the baseband/audioprocessor IC allows it to follow a digital shrink path for cheaperdie while providing more processing power for future algorithmdevelopment. Relying more on software than silicon means fewerexternal components and more PC board real estate to improvemanufacturing costs and reliability. It also means more streamlinedmanufacturing without constant production recalibration.

The Symphony Digital Radio chipset solution can be configured forsingle or dual antenna radio functionality and for single or dualsimultaneous source for playback. (In a car, this means front andrear seat audio.) It consists of one or two RF front-end chips withAM, FM, and Weatherband tuning capability; an all-digital DSPbaseband/audio processor; and an IF Sigma Delta analog to digital(A/D) converter integrated with dual audio A/D and six digital toanalog (D/A) converters for audio inputs and outputs.

There are one or two RF front-end chips with AM, FM andWeatherband tuning capability (200kHz to 165MHz).

Heart of the system

The heart of the system is the baseband/audio processor, whichincorporates special-purpose DSPs and one general-purpose 56300 DSPon a single piece of silicon. All baseband radio and audio processingis performed on this single chip rather than a series of chips.

The integrated baseband/audio processor reduces space and cost. Itprovides digital input ports and Enhanced Serial Audio Interface(ESAI) to connect external DSPs, Digital Analog Converters (DACs) andother devices to accommodate additional features.

An on-board 6-channel asynchronous sample rate converter (ASRC) isused for jitter removal and format conversion. A standalone 2-channelASRC would cost an additional $6 – $10. Also on-board is Sony-PhilipsDigital Interface Format (SPDIF) and a standalone chip to providethis would cost an additional dollar..

Motorola believes that it can supply its customers with a SymphonyDigital Radio platform with advanced capabilities for about the samecost-per-unit as current radios. And it should be available to theconsumer before Christmas 2003!

Published in Embedded Systems (Europe) October2002

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