iir

iir digital filter

Calling Sequence

hz=iir(n,ftype,fdesign,frq,delta)
[p,z,g]=iir(n,ftype,fdesign,frq,delta)

Arguments

:n positive number witn inteher value, the filter order. : :ftype string specifying the filter type, the possible values are:

‘lp’ for low-pass, ‘hp’ for high pass, ‘bp’ for band pass and ‘sb’ for stop band.

: :fdesign string specifying the analog filter design, the possible

values are: ‘butt’, ‘cheb1’, ‘cheb2’ and ‘ellip’

: :frq 2-vector of discrete cut-off frequencies (i.e., 0<frq<.5).

For ‘lp’ and ‘hp’ filters only frq(1) is used. For ‘bp’ and ‘sb’ filters frq(1) is the lower cut-off frequency and frq(2) is the upper cut-off frequency

: :delta 2-vector of error values for cheb1, cheb2, and ellip filters where only delta(1) is used for cheb1 case, only delta(2) is used for cheb2 case, and delta(1) and delta(2) are both used for ellip case. 0<delta(1),delta(2)<1

• for cheb1 filters 1-delta(1)<ripple<1 in passband
• for cheb2 filters 0<ripple<delta(2) in stopband
• for ellip filters 1-delta(1)<ripple<1 in passband and 0<ripple<delta(2) in stopband

: :hz a single input single output discrete transfer function, the low

pass filter

: :p vector of transformed filter zeros. : :z vector of transformed filter poles. : :g a scalar: transformed filter gain. :

Description

function which designs an iir digital filter using `analog filter`_ designs and `bilinear transformation`_ .

Examples

hz=iir(3,'bp','ellip',[.15 .25],[.08 .03]);
[hzm,fr]=`frmag`_(hz,256);
`plot2d`_(fr',hzm')
`xtitle`_('Discrete IIR filter band pass  0.15 < fr < 0.25 ',' ',' ');
q=`poly`_(0,'q');     //to express the result in terms of the delay operator q=z^-1
hzd=`horner`_(hz,1/q)

//Poles Zeros Gain filter representation
[p,z,g]=iir(3,'bp','ellip',[.15 .25],[.08 .03]);
g*`poly`_(z,'z')/`poly`_(p,'z')

See Also

• eqfir minimax approximation of FIR filter
• eqiir Design of iir filters
• analpf create analog low-pass filter
• bilt bilinear or biquadratic transform SISO system given by a zero/poles representation