Realisation of Digital Filters - Digital Signal Processing: A Practitioner's Approach - page 113

regions are marked U. This imposes a limitation on using the entire spectrum, since
roughly 50% of the sampling zones are unstable. If we compromise on the
the sharpness of the filter, then these zones can be reduced. But by compromising
on sharpness, a higher-order FIR filter can probably be used instead of this
structure.

5.6 Real-Time Applications
In real-time applications, a single filter or set of filters operate on the data and have
to provide the results in a specified time demanded by the overall system
requirements. Depending on the time criticality, real-time applications can be
implemented using a single processor or using a combination of processor and
dedicated hardware. The best examples are the FFT chipsets that were very popular
from 1985 to 1993. There are many programable digital filter chips on the market
and they can be interfaced to another processor, which may be of low computing
power, as a trade-off between cost and hardware complexity. With the availability
of powerful processors, almost all the functions can be directly implemented on the
same processor.

5.6.1 Comparison of DSP Processors
Table 5.1 has been compiled from published literature issued by commercial
vendors of DSP processors. 2 One important performance measure is the clock
frequency or million instructions per second (MIPS). At periodic intervals,
Berkeley Design Technolgy Inc. (BDTI) publishes its own processor evaluations
based on benchmark programs it has designed.

Table 5.1 Benchmarking some commercial DSP processors

Feature

Processor Frequency or MIPS BDTI mark

ADI ADSP-2183 52 13

ARM7TDMI/Piccolo 70 14

Hitachi SH-DSP 66 17

Intel Pentium 233 26

Lucent DSP1620 120 22

Lucent DSP16210 100 36

Motorola DSP56011 47.5 13

2 The data is not from a single source but from various DSP processor vendors; it is only informative
in nature.