Second-order IIR notch filter
[num,den] = iirnotch(w0,bw)
[num,den] = iirnotch(w0,bw,ab)
[num,den] = iirnotch(w0,bw) turns
a digital notching filter with the notch located at
and with the bandwidth at the -3 dB point set to
To design the filter,
w0 must meet the condition
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
w0, the frequency
to remove from the signal.
[num,den] = iirnotch(w0,bw,ab) returns
a digital notching filter whose bandwidth,
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.
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); fvtool(b,a);
The notch filter has the desired bandwidth with the notch located at 60 Hz, or 0.4? radians per sample. Compare this plot to the comb filter plot shown on the reference page for iircomb.
Usage notes and limitations:
All inputs must be constant. Expressions or variables are allowed if their values do not change.