Why I am getting negative values in my low pass filter results?

Why I am getting negative values in my low pass filter ?

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Answer 1

[Sam Chak]

Hi @Zahra

Since you asked, I'm guessing the input values are negative.

t = linspace(0, 10, 1001);
lpf = tf(1, [1 1])      % Low-pass Filter

lpf =
 
    1
  -----
  s + 1
 
Continuous-time transfer function.

u   = ones(1, length(t));
lsim(lpf, -u, t), ylim([-1.2 0])