5

Realisation of Digital Filters

Translating difference equations into hardware is an important step in real life, and needs considerable care and attention. There are three distinct elements to this process (Figure 5.1). The first element is conversion of analogue signals to digital numbers; this is accomplished by an analogue-to-digital converter. The second element is implementation of the algorithm; this is carried out in the computing unit. The computing unit may be dedicated hardware made from adders, multipliers and accumulators or it may be a DSP processor. A dedicated unit can be an FPGA unit or a VLSI chip. The third element modifies the output of the computing unit in a manner required for further use in direct digital form or in analogue form. It varies from application to application. Sometimes we may require digitised data for processing.

5.1 Evolution

Hardware realisation of DSP algorithms, or for that matter all the embedded systems, has gone through a revolutionary change in recent years. The reason for this is the phenomenal growth rate of computing power. Clock speeds were around 1 MHz in 1976 whereas today they are 4 GHz or more. Clock speed is a good measure for estimating computing power.

From 1975 to 1985, development was more logic oriented and DSP was always on dedicated hardware. From about 1985 to 1995, it became more software oriented as hardware was becoming standardised while excellent software tools were being created to implement computation-intensive ...

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