# # 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