isminphase
Determine whether filter is minimum phase
Syntax
flag = isminphase(b,a)
flag = isminphase(sos)
flag = isminphase(d)
flag = isminphase(...,tol)
Description
flag = isminphase(b,a)flag, equal to true if
the filter specified by numerator coefficients, b,
and denominator coefficients, a, is a minimum
phase filter.
flag = isminphase(sos)true if the filter specified by second
order sections matrix, sos, is minimum phase. sos is
a K-by-6 matrix, where the number of sections, K,
must be greater than or equal to 2. Each row of sos corresponds
to the coefficients of a second order (biquad) filter. The ith
row of the sos matrix corresponds to [bi(1)
bi(2) bi(3) ai(1) ai(2) ai(3)].
flag = isminphase(d)true if
the digital filter, d, has minimum phase. Use designfilt to generate d based
on frequency-response specifications.
flag = isminphase(...,tol)tol, to determine when two numbers
are close enough to be considered equal. If not specified, tol,
defaults to eps^(2/3).
Examples
Minimum Phase Filters
Design a sixth-order lowpass Butterworth IIR filter using second order sections. Specify a normalized 3-dB frequency of 0.15. Check if the filter has minimum phase.
[z,p,k] = butter(6,0.15); SOS = zp2sos(z,p,k); min_flag = isminphase(SOS)
min_flag = logical
1
Redesign the filter using designfilt. Check that the zeros and poles of the transfer function are on or within the unit circle.
d = designfilt('lowpassiir','DesignMethod','butter','FilterOrder',6, ... 'HalfPowerFrequency',0.25); d_flag = isminphase(d)
d_flag = logical
1
zplane(d)
Given a filter defined with a set of single-precision numerator and denominator coefficients, check if it has minimum phase for different tolerance values.
b = single([1 1.00001]); a = single([1 0.45]); min_flag1 = isminphase(b,a)
min_flag1 = logical
0
min_flag2 = isminphase(b,a,1e-3)
min_flag2 = logical
1
See Also
designfilt | digitalFilter | isallpass | islinphase | ismaxphase | isstable