Implementing IIR/FIR Filters

“The filter
example used is a
sixth-order
Butterworth
lowpass filter
with a cutoff
frequency of
approximately
225 Hz and a
sample
frequency of
1000 Hz.”
SECTION 6
Filter Design and
Analysis System
The following paragraphs discuss the design of a
cascaded filter in both the direct-form and canonic implementations,
using a software package, QEDesign
(formerly FDAS 1 ), available from Momentum Data
Systems, Inc. The filter example used is a sixth-order
Butterworth lowpass filter with a cutoff frequency of
approximately 225 Hz and a sample frequency of
1000 Hz. Figure 6-6 is the log magnitude (gain) plot
from the system output. Figure 6-7 is the phase as a
function of frequency in wrapped format (-π wraps to
+π). In addition, Figure 6-8 is a zero/pole plot, and Figure
6-9 is the group delay, which is the negative of the
derivative of the phase with respect to frequency.
FDAS will also generate an impulse response, step response,
and a linear magnitude plot. The results of the
design are written to a file, FDAS.OUT, which contains
much useful information. The coefficient data is written
to COEFF.FLT. The DSP56001 code generator
(MGEN) reads the COEFF.FLT file and generates a
DSP56001 assembly source file, COEFF.ASM, which
1. All references to FDAS in this application note refer to the
software package QEDesign.
MOTOROLA 6-1