Design of iir filters
[cells,fact,zzeros,zpoles]=eqiir(ftype,approx,om,deltap,deltas)
:ftype filter type ( ‘lp’,’hp’,’sb’,’bp’) : :approx design approximation ( ‘butt’,’cheb1’,’cheb2’,’ellip’) : :om 4-vector of cutoff frequencies (in radians)
om=[om1,om2,om3,om4], 0 <= om1 <= om2 <= om3 <= om4 <= pi .When ftype`=’lp’ or ‘hp’, `om3 and om4 are not used and may be set to 0.
: :deltap ripple in the passband. 0<= deltap <=1 : :deltas ripple in the stopband. 0<= deltas <=1 : :cells realization of the filter as second order cells : :fact normalization constant : :zzeros zeros in the z-domain : :zpoles poles in the z-domain :
Design of iir filter based on syredi.
The filter obtained is h(z)=fact`*product of the elements of `cells.
That is hz=fact*prod(cells.num)./prod(cells.den).
[cells,fact,zzeros,zpoles]=eqiir('lp','ellip',[2*%pi/10,4*%pi/10],0.02,0.001)
h=fact*`poly`_(zzeros,'z')/`poly`_(zpoles,'z')