Dec 14, 2009 #1 J jpm1u Newbie level 1 Joined Dec 13, 2009 Messages 1 Helped 0 Reputation 0 Reaction score 0 Trophy points 1,281 Activity points 1,287 I'm to design a 2nd order, N=2, butterworth HPF starting from the normalized transfer function for a LPF: HN(s)=1/(s^2+1.414*s+1) Given: T=0.004 Ωc=0.8 pi wc=192 pi To find the transfer function of the HPF, substitute s for wc/s: H(s)=HN(wc/s)=s^2/(s^2+853*s+363833) Here's my MATLAB code: Code: T=.8/192; Fs=1/T; nums=[1 0 0]; dens=[1 853.03 363833.1]; figure [Hws,w]=freqs(nums,dens); plot(w,abs(Hws)) [numz,denz]=impinvar(nums,dens,Fs); tf(numz,denz,T) figure [Hwz,w]=freqz(numz,denz); plot(w,abs(Hwz)) The transfer function of my analog filter looks good, but the transfer function of the digital filter is not right. Could someone help please?
I'm to design a 2nd order, N=2, butterworth HPF starting from the normalized transfer function for a LPF: HN(s)=1/(s^2+1.414*s+1) Given: T=0.004 Ωc=0.8 pi wc=192 pi To find the transfer function of the HPF, substitute s for wc/s: H(s)=HN(wc/s)=s^2/(s^2+853*s+363833) Here's my MATLAB code: Code: T=.8/192; Fs=1/T; nums=[1 0 0]; dens=[1 853.03 363833.1]; figure [Hws,w]=freqs(nums,dens); plot(w,abs(Hws)) [numz,denz]=impinvar(nums,dens,Fs); tf(numz,denz,T) figure [Hwz,w]=freqz(numz,denz); plot(w,abs(Hwz)) The transfer function of my analog filter looks good, but the transfer function of the digital filter is not right. Could someone help please?