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Every
physically realizable circuit has a transfer function
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that
is a rational polynomial in s
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We
want to determine classes of rational polynomials that
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approximate
the Ideal low-pass filter response (high-pass
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band-pass
and band-stop filters can be derived from a low pass design)
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Four
well known approximations are discussed here:
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Butterworth:
Steven Butterworth,"On the Theory of Filter Amplifiers",
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Wireless
Engineer (also called Experimental Wireless and the Radio
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Engineer),
vol. 7, 1930, pp. 536-541
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Chebyshev:
Pafnuty Lvovich Chebyshev (1821-1894) - Russia
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Cyrillic
alphabet - Spelled many ways
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Elliptic
Function: Wilhelm Cauer (1900-1945) - Germany
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U.S.
patents 1,958,742 (1934), 1,989,545 (1935), 2,048,426 (1936)
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Bessel:
Friedrich Wilhelm Bessel, 1784 - 1846
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