iir

Arguments

n

positive number witn integer 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 (in this case, frq can be a scalar). For 'bp' and 'sb' filters frq(1) is the upper cut-off frequency and frq(2) is the lower 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 poles.

z

vector of transformed filter zeros.

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