2015/11/14 频率特性的求取一传递函数法（续） a- AG(-j@) 2j Q= AG(j@) 2j X(t)=ae-jo+aelou →F0=G(j@=G(sL=0 School of Mechanical Engineering Me369-Lecture 7.1 Shanghai Jiao Tong University Fall 2015 [例1]频率特性的物理含义一RC电路 i) G(s)= U2(s)1 U (s)1+Ts () U,(jo) 1 G(io)= U(jo)1+joT A(@)=G(j@)= 1 T=RC V+(ToY o(@)=LG(j@)=arctan(-@T) 低频信号(oT<1) 高频信号 (oT>1) School of Mechanical Engineering Me369-Lecture 7.1 Shanghai Jiao Tong University Fall 2015 42015/11/14 4 Me369-Lecture 7.1 Fall 2015 School of Mechanical Engineering Shanghai Jiao Tong University ( ) j t j t c x t ae ae      ( ) 2 AG j a j     ( ) 2 AG j a j    F()= G(j  )=G(s)|s=jω 频率特性的求取—传递函数法（续） Me369-Lecture 7.1 Fall 2015 School of Mechanical Engineering Shanghai Jiao Tong University [例1]频率特性的物理含义—RC 电路 2 1 ( ) 1 ( ) ( ) 1 U s G s U s Ts    T RC  2 1 ( ) 1 ( ) ( ) 1 U j G j U j j T        2 1 ( ) | ( ) | 1 ( ) A G j T           ( ) ( ) arctan( )     G j T ( 1) T  ( 1) T  低频信号 高频信号