Analog Filters, Software-Based and

Owing to the way that analog and digital filters are physically
implemented, an analog filter is inherently more size-and
power-efficient, although more component-sensitive, than its
digital counterpart - if it can be implemented in a
straightforward manner. In general, as signal frequency
increases, the disparity in efficiency increases.
Characteristics of applications where digital filters are more
size and power efficient than analog filters are: linear phase,
very high stop band attenuation, very low pass band ripple;
the filter’s response must be programmable or adaptive; the
filter must manipulate phase and, very low shape factors (a
digital filter’s shape factor is the ratio of the filter’s pass band
width plus the filter’s transition band width to the filter’s pass
band width).
General-purpose digital signal microprocessors, now
commodity devices, are used in a broad range of
applications and can implement moderately complex digital
filters in the audio frequency range. Many standard signal
processing algorithms, including digital filters, are available
in software packages from digital signal processor and third
party vendors. As a result, software development costs are
trivial when amortized over production quantities.
The architectures of digital signal microprocessors are
usually optimized to perform a sum-of-products calculation
with data from RAM or ROM. They are not optimized for any
specific DSP function. However, to get extended sampling
rate performance from a digital filter requires hardware
designed to perform the intended filter function at the
desired sampling frequencies.
For example, Intersil Corporation offers a family of standard
digital filter products with several others in development.
Some hardware-specific digital filters can now sample at
rates approaching 75 Megasamples Per Second (MSPS).
Higher performance is possible for high volume applications
by limiting the range of parameters. Standard filter products
strike a balance between optimized filter architectures and
programmability by offering a line of configurable filters. That
is, these products are function-specific, with optimized
architectures and programmable parameters.