L()=-20g√(1-o2/on2)2+42(o/on)2 0<<0时L(o)≈0 o>>0,fL(O--40lgo/o,=-40(g O-Ig On) 240/ P(o)=-arctg 1-(a/on)2 (dB 40 40dB/dec 20 0.1 0/0 20 40dB/dec 180 1o/0a L.。J 18 图512振荡环节的对数坐标图• ω<<ωn时L(ω)≈0 • ω>>ωn时L(ω)≈-40lgω/ωn =-40(lg ω-lg ωn ) 2 2 2 2 2 ( ) 20lg (1 / ) 4 ( / ) L  = − −  n +    n 2 1 ( / ) 2 / ( ) n n arctg        − = − 1 10 10 图5.12 振荡环节的对数坐标图 ω/ωn 0.1 (dB) 0 1 40 -20 40dB/dec -40dB/dec ( o ) 180 -180 0 0.1 ω/ωn 20