Page 305 - Analog and Digital Filter Design
P. 305
302 Analog and Digital Filter Design
The filter order is then required. If a Chebyshev type has been requested, the
program only allows odd-order designs (orders: three, five, seven, and nine). If
a Butterworth or Bessel type has been selected, the program will allow any order
from three to nine.
The load impedance is entered next, which is also the source impedance since
the terminations are equal. This can be entered as an exponent (i.e., 1.2e3) or
as a value and coefficient (i.e., 1.2k).
Finally, the “Q” of the inductors is required. This may be required for a circuit
analysis program, and any integer value from “1” to “999” can be entered.
The program displays the filter parameters and seeks approval before designing
the filter.
It also asks, for lowpass or highpass designs, whether an inductor or a capaci-
tor is required for the first component. In the case of bandpass or bandstop
designs, it asks whether the first arm in the ladder filter should be a series or
parallel resonant circuit. These choices affect the filter’s input impedance outside
the passband.
A component list is displayed, with some explanation about the component’s
location. An option is given to save the design; the default file name is “filter.ckty’
but users are prompted to choose another name for this file if they wish.
Ellipse
Ellipse.exe is a passive filter design program. This program only designs Cauer
(elliptical) filters with odd order.
The user is prompted to enter a choice of highpass, lowpass, bandpass, or band-
stop. Entry is a number from one to four.
The filter order is required next. An odd number is required from three to nine
(i.e., 3, 5, 7, or 9).
Next enter the required source and load impedance (the program asks for the
load impedance, but only equally terminated filters can be designed so the source
impedance is the same value). Any integer value between “1” and “10,000” can
be entered.
The steepness of the filter response skirt is required next. The choice is expressed
as an angle: 30°, 40”, 50°, or 60”. The greater the angle, the steeper the skirt.
