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The magical world of DSP

Posted: 16 Jun 2003 ?? ?Print Version ?Bookmark and Share

Keywords:dsp? dsp silicon architecture? microprocessor? vlsi circuit? ram?

The portability of "multimedia" visual and aural signals, and the human brain's consequent capacity to process and store them, are fundamental to our well-being and advancement. The generation, processing, storage and transmission of signals from an array of origins to a diversity of areas of reception has been enabled by miraculous advances in understanding the nature of human sensory perception coupled with advances in the semiconductor industry.

In recent years, much attention has been given to the use of DSP in telecom and entertainment systems. This is due to the increasing affordability of VLSI circuits with their properties of small size, low power, noise immunity and reliability.

It was in 1978 when I first developed an audio mixing system to input 48 channels and then process, mix and output them to stereo channels. The task was to convert from an analog product to an all-digital one. Emergent in the market were a few rudimentary MPUs, a multiplier on a 64-pin dual-in-line package, bit-slice processors to build Lego brick-style signal processing systems, RAM and ROM chips, and ADCs and DACs that converted to and from 16bit audio at 50ksamples/sec respectively.

My first system achieved a board clock speed of around 7MHz, from which I could execute 142 customized instructions between audio samples per channel. Each of a set of four parametric equalizers consumed 19 instructions to shape the signal, leaving some instructions for checking, routing and panning the signals in stereo space and mixing them. The selling price, including racks and console metalware/woodwork was $400,000. The system required a room.

Today, similar processing would occupy real estate less than a PC motherboard with metalware and plastic, and would cost a hundred times less. Bit-sliced processors have been increasingly replaced by standardized architectures executing more parallel operations. The multiplier has been swallowed into the processor, and wire connections have been replaced by semicolon keystrokes in a C-compilable program of the native instruction set. Now we can build more sophisticated systems even with attendant video processing. Moreover, functions can easily be changed.

The need to transmit signals from source to destination at low cost, high fidelity and at faster speed is a driving force in DSP. Transmitting an uncompressed audio stereo channel requires 1,600Kbps. With signal compression algorithms of today, transmissions can occur at 64Kbps to 128Kbps using 100MHz of DSP power. Signals need to be examined and correlated to squeeze out information. These operations require more memory. Hence, memory structures are the seas and processing cores are the islands in today's DSP silicon architectures.

The entry ticket to the magical world of DSP is to sample the signal at least twice its bandwidth. The signal, converted to a series of binary numbers, is processed in a computing environment with adequate memory - limitations being the processing rate and precision vis-`-vis the audio samples. It can perform tricks to transmit signals over a crowded or limited transmission or storage medium.

No hard limit to semiconductor technology is yet around the corner. New product developments with multiple DSP cores and standardized interfaces for wireless communication applications, such as ST's Nomadik and TI's OMAP, are adequate testimony. However, with the increasing system complexities, development focus for successful market entry will have to shift gear to architecture standardization, design methodology, software management complexity and IP reuse.

- Kay Das

Singapore R&D Center Director

STMicroelectronics Inc.

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