→N(A) 2-4M N k2/ N (5)变增益特性的描述函数N(A)=N1(A)+N2(A) =M1(4)-N12(A)+N13(A)+N2(A) N1(A)=k1 A1=0,A0=0 k, Asin wt sin wtdwtM = −1 （5）变增益特性的描述函数 ( ) ( ) ( ) N A = N1 A + N2 A = ( ) ( ) ( ) ( ) N11 A − N12 A + N13 A + N2 A 11 1 N (A) = k A1 = 0, A0 = 0 B k Asin wtsin wtdwt 1 2 0 1 =  1   2 0 2 4 0 1 ( ) 4 ( ) A Me j A e A M N A   = − −