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#
# Copyright 2008 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# GNU Radio is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3, or (at your option)
# any later version.
#
# GNU Radio is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING. If not, write to
# the Free Software Foundation, Inc., 51 Franklin Street,
# Boston, MA 02110-1301, USA.
#
# See Altera Application Note AN455
#
# R = decimation factor, 8-256
# Fc = passband (one-sided) cutoff frequency
# L = number of taps
function taps = cic_comp_taps(R, Fc, L)
M = 1; %% Differential delay
N = 4; %% Number of stages
B = 18; %% Coeffi. Bit-width
Fs = 64e6; %% (High) Sampling freq in Hz before decimation
Fo = R*Fc/Fs; %% Normalized Cutoff freq; 0<Fo<=0.5/M;
p = 2e3; %% Granularity
s = 0.25/p; %% Step size
fp = [0:s:Fo]; %% Pass band frequency samples
fs = (Fo+s):s:0.5; %% Stop band frequency samples
f = [fp fs]*2; %% Normalized frequency samples; 0<=f<=1
Mp = ones(1,length(fp)); %% Pass band response; Mp(1)=1
Mp(2:end) = abs( M*R*sin(pi*fp(2:end)/R)./sin(pi*M*fp(2:end))).^N;
Mf = [Mp zeros(1,length(fs))];
f(end) = 1;
h = fir2(L,f,Mf); %% Filter length L+1
taps = h/sum(h); %% Floating point coefficients
endfunction
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