线性时不变系统

LTI System Linear Time Invariant

\begin{aligned} o {α f_{1} (t)} & = α x_{1} (t) \\ o {f_{1} (t) + f_{2} (t)} & = x_{1} (t) + x_{2} (t) \\ o {α_{1} f_{1} (t) + α_{2} f_{2} (t)} & = α_{1} x_{1} (t) + α_{2} x_{2} (t) \end{aligned}

叠加原理

\begin{aligned} o {f (t)} & = x (t) \\ o {f (t - τ)} & = x (t - τ) \end{aligned}

系统的输出信号在时间上的延迟等于输入信号在时间上的延迟