User`s guide

Control System Parts 6
-11
Cheb
y
shev Filters
The Chebyshev filters allow filtering of the signal based on a set
of frequency characteristics. The output of a Chebyshev filter
depends upon the analysis being done.
For DC and bias point, the output is simply the DC response of
the filter. For AC analysis, the output for each frequency is the
filter response at that frequency. For transient analysis, the
output is then the convolution of the past values of the input with
the impulse response of the filter. These rules follow the
standard method of using Fourier transforms.
Note
PSpice A/D computes the impulse response of
each Chebyshev filter used in a transient analysis
durin
g
circuit read-in. This may require
considerable computin
g
time. A messa
g
e is
displayed on your screen indicatin
g
that the
computation is in pro
g
ress.
Note
To obtain a listin
g
of the filter Laplace coefficients
for each sta
g
e, select Setup from the Analysis
menu, click on Options, and enable LIST in the
Options dialo
g
box.
Each of the Chebyshev filter parts is described in the following
pages.
LOPASS
The LOPASS part is characterized by two cutoff frequencies
that delineate the boundaries of the filter pass band and stop
band. The attenuation values, RIPPLE and STOP, define the
maximum allowable attenuation in the pass band, and the
minimum required attenuation in the stop band, respectively.
The LOPASS part provides one input and one output.
Figure 6-1 shows an example of a LOPASS filter device. The
filter provides a pass band cutoff of 800 Hz and a stop band
cutoff of 1.2 kHz. The pass band ripple is 0.1 dB and the
FS stop band frequency
FP pass band frequency
RIPPLE pass band ripple in dB
STOP stop band attenuation in dB
MicroSim recommends lookin
g
at one or more of the references
cited in
Frequency-Domain
Device Models on page 6-35, as
well as some of the followin
g
references on analo
g
filter
desi
g
n:
1
Ghavsi, M.S. & Laker, K.R.,
Modern Filter Desi
g
n
,
Prentice-Hall, 1981.
2
Gre
g
orian, R. & Temes, G.,
Analo
g
MOS Inte
g
rated
Circuits
, Wiley-Interscience,
1986.
3
Johnson, David E.,
Introduction to Filter Theory
,
Prentice-Hall, 1976.
4
Lindquist, Claude S.,
Active
Network Desi
g
n with Si
g
nal
Filterin
g
Applications
,
Steward & Sons, 1977.
5
Stephenson, F.W. (ed),
RC
Active Filter Desi
g
n
Handbook
, Wiley, 1985.
6
Van Valkenbur
g
, M.E.,
Analo
g
Filter Desi
g
n
, Holt,
Rinehart & Winston, 1982.
Fi
g
ure 6-1
LOPASS Filter
Example