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Pioneering EE Patent, featured Dec. 1-14
"Programmable Digital Signal Processor"
Issued 1974 to Westinghouse for the first DSP with saturation
arithmetic.
Get a free abridged copy of this historic patent
(or just view a summary) at http://eepatents.com/feature/?m12d01
Browse the entire collection at http://eepatents.com/collection.html

Many pioneering contributions to EE design gradually become
commonplace and buried in "off-the-shelf" components, to the point
where we forget their importance to achieving the end result. One such
invention is the "self-saturating number representation" provided in
DSPs. This ubiquitous feature allows sums of products to saturate to a
maximum value when signals become excessively strong. Saturation
mimics the behavior of analog amplifiers, which are said to "rail out"
at a maximum signal level. Without saturation arithmetic in a DSP,
overflowing sums would wrap around (as only binary numbers, and not
signals, do) and produce unpredictable and undesirable outputs. 

This patent is interesting for its claim to saturation arithmetic, and
also for its early disclosure of the general-purpose DSP, which is
enjoying unprecedented popularity 25 years later.

Ed Suominen
Registered Patent Agent
Former R&D Engineer, RF/DSP
Web Site: http://eepatents.com