iirnotch
Second-order IIR notch filter
Description
[
returns the numerator coefficients, num,den] = iirnotch(w0,bw)num, and the denominator
coefficients, den, of the digital notching filter with the notch
located at w0 and the bandwidth at the –3 dB point set to
bw. To design the filter, w0 must meet the
condition 0.0 < w0 < 1.0, where 1.0 corresponds to π radians per
sample in the frequency range.
The quality factor (Q factor) q for the filter is related to the
filter bandwidth by q = w0/bw, where
w0 is the notch frequency.
[
returns the digital notching filter whose bandwidth, num,den] = iirnotch(w0,bw,ab)bw, is specified at
a level of –ab decibels. Including the optional input argument
ab lets you specify the magnitude response bandwidth at a level that is
not the default –3 dB point, such as –6 dB or 0 dB. If not specified,
ab defaults to the –3 dB width
(10log10(1/2)).
Examples
Design IIR Notch Filter Using iirnotch
Design and plot an IIR notch filter that removes a 60 Hz tone (f0) from a signal at 300 Hz (fs). For this example, set the Q factor for the filter to 35 and use it to specify the filter bandwidth.
wo = 60/(300/2); bw = wo/35; [b,a] = iirnotch(wo,bw);
The notch filter has the desired bandwidth with the notch located at 60 Hz, or radians per sample. Compare this plot to the comb filter plot shown for iircomb.
fvtool(b,a)
