Matlab z-transform Bode plot

  • MATLAB
  • Thread starter bmalp
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  • #1
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Main Question or Discussion Point

Hi,

I try to visualize a sine wave, z-transformed in a Bode plot. The frequency shows up correctly, but the amplitude is way off - why?

Thanks for your comments.
Bmalp



function zdemo

format compact
syms w Ts n z phi t

Ts = 1
w = 0.1
phi = 0

vz = simplify(ztrans(sin(w*n*Ts+phi))) % correct

if 0 % method 1
[num,den] = numden(simplify(vz));
num = collect(num,'z')
den = collect(den,'z')
num1 = sym2poly(num)
den1 = sym2poly(den)
[h,w] = freqz(num1,den1,512,'whole');
else % method 2
fs = 1;
f = linspace(0,fs,256);
w = 2*pi*f;
ss = sqrt(-1)*w;
Z = exp(ss/fs);
h = double(subs(vz,z,Z));
end
plot(w,abs(h)) % amplitude way too big
 

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