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