Obtain the input impulse response h(t) and the system function H(s) of your system
A very simple one:
$ y(t)=\int_{-\infty}^{\infty}x(t)dt $
We can get $ h(t)=u(t)\, $
A very simple one:
$ y(t)=\int_{-\infty}^{\infty}x(t)dt $
We can get $ h(t)=u(t)\, $