电流镜cascode结构的shielding作用是指什么

哪位大虾知道电流镜中的cascode结构的shielding作用具体指什么，最好有推导公式来说明，没有也可以，大家尽量发表一下，百度上貌似找不到这方面的知识，谢谢
补充：电流镜中的cascode结构的shielding作用可以得到两个nmos管的源极电压相等。

看Razavi的书3.5节, 专门讲了电流镜的Shielding Property

教科书上有啊。呵呵

because of the big rout

If you have a very large impedance between two nodes, than any voltage wiggles on one end will not affect the other end.  So it has a shileding property.
That extra transistor when it is working in saturation exhibits a large rout, hence shielding the bottom transistor.

不知道，同问