function [b,a]=u_buttap(N,Omegac);%非歸一化Butterworth模擬低通濾波器原型設(shè)計(jì)
         [z,p,k]=buttap(N);
         p=p*Omegac;
         k=k*Omegac^N;
         B=real(poly(z));
         b0=k;
         b=k*B;
         a=real(poly(p));