abc.m

filter design sigma delta filter

%abc——为求取a1、a2、a3、a4得系数组，使其于（0.5～0.1）范围内，且使系统保持稳定——极点范围<0.98
clear
c=0;
for i0=2:10
    for i1=2:10
        for i2=2:10
            for i3=2:10
                a=[1/i0 1/i1 1/i2 1/i3];
                A1=a(1);
                A2=-3*a(1)+a(1)*a(2);
                A3=3*a(1)-2*a(2)*a(1)+a(1)*a(2)*a(3);
                A4=-a(1)+a(1)*a(2)-a(1)*a(2)*a(3)+a(1)*a(2)*a(3)*a(4);
                p=[1 A1-4 A2+6 A3-4 A4+1];
                h=abs(roots(p));%求出四个极点给数组h
                if ((h(1)<0.98)&(h(2)<0.98)&(h(3)<0.98)&(h(4)<0.98)) %判别系统是否稳定
                    c=c+1;
                    d(c,:)=a;
                else
                end
            end
        end
    end
end