iirlinphase

Quasi-linear phase IIR filter from halfband filter specification

Syntax

hd = design(d,'iirlinphase')
hd = design(...,'filterstructure',structure)

Description

hd = design(d,'iirlinphase') designs a quasi-linear phase filter hd specified by the filter specification object d.

hd = design(...,'filterstructure',structure) returns a filter with the structure specified by structure. By default, the filter structure is df2sos (direct-form II with second-order sections). You can substitute one of the following strings for structure to specify the structure of hd.

Structure String

Filter Structure

df1sos

Direct-form I IIR filter with second-order sections

df2sos

Direct-form II IIR filter with second-order sections

df1tsos

Transposed direct-form I IIR filter with second-order sections

df2tsos

Transposed direct-form II IIR filter with second-order sections

Examples

Design a quasi-linear phase, minimum-order halfband IIR filter with transition width of 0.36 and stopband attenuation of at least 80 dB.

tw = 0.36;
ast = 80;
d = fdesign.halfband('tw,ast',tw,ast); % Transition width, 
                                    % stopband attenuation.
hd = design(d,'iirlinphase');
fvtool(hd)

Notice the characteristic halfband nature of the ripple in the stopband. If you measure the resulting filter, you see it meets the specifications.

measure(hd)     

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