[Commit-gnuradio] r8185 - gnuradio/trunk/gnuradio-core/src/utils

[jcorgan]

Author: jcorgan
Date: 2008-04-11 13:47:54 -0600 (Fri, 11 Apr 2008)
New Revision: 8185

Added:
   gnuradio/trunk/gnuradio-core/src/utils/cic_comp_taps.m
Modified:
   gnuradio/trunk/gnuradio-core/src/utils/Makefile.am
Log:
Added CIC compensation filter tap generator.  Useful when working without the 
half-band filter in the USRP.

Modified: gnuradio/trunk/gnuradio-core/src/utils/Makefile.am
===================================================================
--- gnuradio/trunk/gnuradio-core/src/utils/Makefile.am  2008-04-11 15:50:32 UTC 
(rev 8184)
+++ gnuradio/trunk/gnuradio-core/src/utils/Makefile.am  2008-04-11 19:47:54 UTC 
(rev 8185)
@@ -22,6 +22,7 @@
 include $(top_srcdir)/Makefile.common
 
 EXTRA_DIST =                   \
+       cic_comp_taps.m         \
        db_width.m              \
        filter_tools.m          \
        plot_freq_response.m    \

Added: gnuradio/trunk/gnuradio-core/src/utils/cic_comp_taps.m
===================================================================
--- gnuradio/trunk/gnuradio-core/src/utils/cic_comp_taps.m                      
        (rev 0)
+++ gnuradio/trunk/gnuradio-core/src/utils/cic_comp_taps.m      2008-04-11 
19:47:54 UTC (rev 8185)
@@ -0,0 +1,45 @@
+#
+# 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