September 29, 2005 -- A simple categorization assigns most
signal-processing blocks to one of two groups. On the one hand are generic
functions, such as op amps and ADCs, which perform one task and may serve in
many disparate applications. On the other hand are application-specific blocks,
such as GSM transceivers and 802.11 basebands, that have narrow definitions at a
much higher level of functional abstraction and, therefore, perform a more
complex set of tasks for only one application. An interesting and growing number
of signal-processing blocks lie somewhere in the middle. Further
scrutiny reveals that the two categories actually lie on a continuum
characterized by a dominantly bimodal distribution with a small but decidedly
nonzero population between the groups.
The way designers interact with instances from the two large groups is
likewise distinct. Tables of parametric performance characterize single-function
generic parts under operating conditions that their manufacturers specify. Part
of the design task, then, includes deriving expected circuit-level behaviors
from topological analysis and components' spec-table performance. On the other
end of the spectrum, conformance to industry standards defines many
application-specific blocks. Individual parametric measures may be difficult to
extract and impossible to control beyond simply choosing one part over another.
In the sparsely populated middle, however, lie parts not given to such easy
description. These flexible bits of silicon can take on behavioral attributes
that depend on an OEM designer's programming or configuration decisions. But,
unlike general-purpose programmable devices, these devices operate at a higher
level of abstraction than bytes and words, instantaneous voltages, or individual
samples. Instead, these devices operate at a level in which the signal is itself
parametric, defined by concepts such as, for example, spectral shape or dynamic
behavior. In other words, the functions that these parts offer are not fully
defined until you decide what you want them to be, and, unlike with
general-purpose signal processors, with these devices, you express those
decisions in application-relevant parametric terms.
By Joshua Israelsohn, EDN Technical Editor
This brief introduction has been excerpted from the original copyrighted article.
View the entire article on the EDN Magazine website.