Realisation of Digital Filters - Digital Signal Processing: A Practitioner's Approach - page 101

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 algorithms on single or multiple
processors. From 1995 to the present, the line between hardware and software
has become very narrow. For that matter, entire design is carried out on electronic
design automation (EDA) tools using new methodologies like co-simulation,
reducing the design cycle time and providing more time for testing, thus ensuring
that the overall system performs closely to the desired specifications.