Effective Z0 与 Impedance Z0 为什么不一样？

各位大虾，小弟想请教一个问题。
在我用HyperLynx仿真的之前，设置好了目标阻抗Z0，当用Terminator Wizard计算匹配电阻的时候，实际的有效电阻（Effective Z0）却比目标阻抗（Impedance  Z0 ）小，不知道这是为什么?

The average metal Z0 is not the same as the effective impedance of a trace. The Average Zo is  Average impedance of the whole trace
The "effective Z0" is a figure that attempts to show by how much the selected nets actual characteristic impedance is effectively lowered by the presence of IC capacitance along the net and associated nets. This value can be used as a guide when choosing termination resistances, since for nets that are significantly loaded by IC capacitance, the proper termination value is almost always lower than suggested by the nets actual Z0.
走线的impedance（Z0) 受到IC impedance 影响= Effective Impedance.
Effective Impedance 一般比走线Impedance 低

多谢啊~