#
-# Copyright 2004,2005 Free Software Foundation, Inc.
+# Copyright 2004,2005,2009 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
and Barrie W. Jervis, Adison-Wesley, 1993. ISBN 0-201-54413-X.
'''
-import math
+import math, cmath
from gnuradio import gr
remez = gr.remez
# ----------------------------------------------------------------
+## Builds a low pass filter.
+# @param gain Filter gain in the passband (linear)
+# @param Fs Sampling rate (sps)
+# @param freq1 End of pass band (in Hz)
+# @param freq2 Start of stop band (in Hz)
+# @param passband_ripple_db Pass band ripple in dB (should be small, < 1)
+# @param stopband_atten_db Stop band attenuation in dB (should be large, >= 60)
+# @param nextra_taps Extra taps to use in the filter (default=2)
def low_pass (gain, Fs, freq1, freq2, passband_ripple_db, stopband_atten_db,
- nextra_taps=0):
+ nextra_taps=2):
passband_dev = passband_ripple_to_dev (passband_ripple_db)
stopband_dev = stopband_atten_to_dev (stopband_atten_db)
desired_ampls = (gain, 0)
(n, fo, ao, w) = remezord ([freq1, freq2], desired_ampls,
[passband_dev, stopband_dev], Fs)
+ # The remezord typically under-estimates the filter order, so add 2 taps by default
taps = gr.remez (n + nextra_taps, fo, ao, w, "bandpass")
return taps
-# FIXME high_passs is broken...
-def high_pass (Fs, freq1, freq2, stopband_atten_db, passband_ripple_db,
- nextra_taps=0):
- """FIXME: broken"""
+## Builds a band pass filter.
+# @param gain Filter gain in the passband (linear)
+# @param Fs Sampling rate (sps)
+# @param freq_sb1 End of stop band (in Hz)
+# @param freq_pb1 Start of pass band (in Hz)
+# @param freq_pb2 End of pass band (in Hz)
+# @param freq_sb2 Start of stop band (in Hz)
+# @param passband_ripple_db Pass band ripple in dB (should be small, < 1)
+# @param stopband_atten_db Stop band attenuation in dB (should be large, >= 60)
+# @param nextra_taps Extra taps to use in the filter (default=2)
+def band_pass (gain, Fs, freq_sb1, freq_pb1, freq_pb2, freq_sb2,
+ passband_ripple_db, stopband_atten_db,
+ nextra_taps=2):
+ passband_dev = passband_ripple_to_dev (passband_ripple_db)
+ stopband_dev = stopband_atten_to_dev (stopband_atten_db)
+ desired_ampls = (0, gain, 0)
+ desired_freqs = [freq_sb1, freq_pb1, freq_pb2, freq_sb2]
+ desired_ripple = [stopband_dev, passband_dev, stopband_dev]
+ (n, fo, ao, w) = remezord (desired_freqs, desired_ampls,
+ desired_ripple, Fs)
+ # The remezord typically under-estimates the filter order, so add 2 taps by default
+ taps = gr.remez (n + nextra_taps, fo, ao, w, "bandpass")
+ return taps
+
+
+## Builds a band pass filter with complex taps by making an LPF and
+# spinning it up to the right center frequency
+# @param gain Filter gain in the passband (linear)
+# @param Fs Sampling rate (sps)
+# @param freq_sb1 End of stop band (in Hz)
+# @param freq_pb1 Start of pass band (in Hz)
+# @param freq_pb2 End of pass band (in Hz)
+# @param freq_sb2 Start of stop band (in Hz)
+# @param passband_ripple_db Pass band ripple in dB (should be small, < 1)
+# @param stopband_atten_db Stop band attenuation in dB (should be large, >= 60)
+# @param nextra_taps Extra taps to use in the filter (default=2)
+def complex_band_pass (gain, Fs, freq_sb1, freq_pb1, freq_pb2, freq_sb2,
+ passband_ripple_db, stopband_atten_db,
+ nextra_taps=2):
+ center_freq = (freq_pb2 + freq_pb1) / 2.0
+ lp_pb = (freq_pb2 - center_freq)/1.0
+ lp_sb = freq_sb2 - center_freq
+ lptaps = low_pass(gain, Fs, lp_pb, lp_sb, passband_ripple_db,
+ stopband_atten_db, nextra_taps)
+ spinner = [cmath.exp(2j*cmath.pi*center_freq/Fs*i) for i in xrange(len(lptaps))]
+ taps = [s*t for s,t in zip(spinner, lptaps)]
+ return taps
+
+
+## Builds a band reject filter
+# spinning it up to the right center frequency
+# @param gain Filter gain in the passband (linear)
+# @param Fs Sampling rate (sps)
+# @param freq_pb1 End of pass band (in Hz)
+# @param freq_sb1 Start of stop band (in Hz)
+# @param freq_sb2 End of stop band (in Hz)
+# @param freq_pb2 Start of pass band (in Hz)
+# @param passband_ripple_db Pass band ripple in dB (should be small, < 1)
+# @param stopband_atten_db Stop band attenuation in dB (should be large, >= 60)
+# @param nextra_taps Extra taps to use in the filter (default=2)
+def band_reject (gain, Fs, freq_pb1, freq_sb1, freq_sb2, freq_pb2,
+ passband_ripple_db, stopband_atten_db,
+ nextra_taps=2):
+ passband_dev = passband_ripple_to_dev (passband_ripple_db)
+ stopband_dev = stopband_atten_to_dev (stopband_atten_db)
+ desired_ampls = (gain, 0, gain)
+ desired_freqs = [freq_pb1, freq_sb1, freq_sb2, freq_pb2]
+ desired_ripple = [passband_dev, stopband_dev, passband_dev]
+ (n, fo, ao, w) = remezord (desired_freqs, desired_ampls,
+ desired_ripple, Fs)
+ # Make sure we use an odd number of taps
+ if((n+nextra_taps)%2 == 1):
+ n += 1
+ # The remezord typically under-estimates the filter order, so add 2 taps by default
+ taps = gr.remez (n + nextra_taps, fo, ao, w, "bandpass")
+ return taps
+
+
+## Builds a high pass filter.
+# @param gain Filter gain in the passband (linear)
+# @param Fs Sampling rate (sps)
+# @param freq1 End of stop band (in Hz)
+# @param freq2 Start of pass band (in Hz)
+# @param passband_ripple_db Pass band ripple in dB (should be small, < 1)
+# @param stopband_atten_db Stop band attenuation in dB (should be large, >= 60)
+# @param nextra_taps Extra taps to use in the filter (default=2)
+def high_pass (gain, Fs, freq1, freq2, passband_ripple_db, stopband_atten_db,
+ nextra_taps=2):
passband_dev = passband_ripple_to_dev (passband_ripple_db)
stopband_dev = stopband_atten_to_dev (stopband_atten_db)
desired_ampls = (0, 1)
(n, fo, ao, w) = remezord ([freq1, freq2], desired_ampls,
[stopband_dev, passband_dev], Fs)
+ # For a HPF, we need to use an odd number of taps
+ # In gr.remez, ntaps = n+1, so n must be even
+ if((n+nextra_taps)%2 == 1):
+ n += 1
+
+ # The remezord typically under-estimates the filter order, so add 2 taps by default
taps = gr.remez (n + nextra_taps, fo, ao, w, "bandpass")
return taps
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