DESIGN AND ANALYSIS OF ANALOG FILTERS A Signal ...

A Signal Processing Perspective 15
1.4 HISTORICAL PERSPECTIVE
Analog electric filters have been in use since the very early days of electrical
engineering. Simple resonant filters, although perhaps not explicitly called such at the
time, were used in radio communications before the introduction of the first active
devices. For example, an early interference suppression circuit introduced by
Marconi, called the X Stopper, was actually a bandpass filter (Blake, 1974).
However, it appears that the first systematic design approaches date from the
first couple decades of this century when K.W. Wagner in Germany, and George
Ashley Campbell (Campbell, 1911; Campbell, 1922) in the United States, independently
developed such approaches to filter design (Darlington, 1984; Stephenson,
1985; Van Valkenburg, 1982). 9 Other methods (such as insertion-loss synthesis)
were introduced by Darlington in the United States and Cauer in Germany in the
1930s (Cauer, 1939; Darlington, 1939) with contributions also by Brune (Brune,
1931; Brune, 1932). Also during the 1930s and 1940s, the beginnings of active filter
design occurred, as introduced by Black, Bode (Bode, 1945), and others.
During this same time period analog filter design procedures were formalized,
such as what is now known as the Butterworth filter (Butterworth, 1930), and elliptic
filters (Cauer, 1931; Norton, 1937; Weinberg, 1962). Bessel filters, based upon
Bessel (lived 1784-1846) polynomials (Krall and Frink, 1949; Grosswald, 1951;
Burchnall, 1951), were introduced by Thomson and Storch (Thomson, 1949;
Thomson, 1959; Storch, 1954). Chebyshev filters, and inverse Chebyshev (also
called Chebyshev type II) filters, based upon Chebyshev polynomials (Chebyshev,
1899), were developed during the 1950s (Cauer, 1958; Henderson and Kautz, 1958;
Stephenson, 1985; Storer, 1957; Weinberg, 1962). 10
In more recent years there has been development in analog filter design
primarily along three lines: (1) introducing additional filter transfer function types
exhibiting refinements, in some sense, compared with classical filters, (2) introducing
computer-aided procedures for simulation, optimization, etc., and (3) circuit
implementation. Since (1) is of primary concern with the emphasis of this book, with
a signal processing perspective, only it will be expanded on in this historical review.
Although it would not be useful to attempt an exhaustive list of filter transfer function
types, a few of the more significant ones (in the author's opinion) will serve to
indicate this further development. The author apologizes in advance for any
significant filter transfer function types inadvertently left out. The order of mention
is mostly chronological within two groupings: (1) general, where the primary concern
9
A brief biographical sketch of Campbell, with some discussion of his early contributions to filter design,
is given by Brittain (1992).
10
A brief biographical sketch of Cauer, with a tribute to his contributions, has been given by Fettweis
(1995).
Section 1.4 Historical Perspective