Cascold电流镜

nieniejun

Cascold电流镜 输出电压下降，哪个管子先进入线性区，为什么？谢谢

MustafaSami

M2 will enter the triode region first.

As M2 drain voltage (Vd2=Vout) drops, and its gate voltage (Vg2=Vin) is constant, two things should happen:

1) Drain voltage of M1 is pinned as VGS2 is constant (Vin-Vth) --> So M1 is still maintained in SAT region.
2) VGD2 should be smaller than Vth, so if the difference increased beyond Vth (as Vout drops, Vin-Vout increases) then M2 will enter Triode region.

Hope this helps  

vaeping123

拉扎维P129页
假设下面的管子M1先进入线性区，Vds减小而Vgs1是不变的，那么Id1会下降。Id1和Id2下降但是Vd1下降说明VGs2是上升的。显然不成立，所以M2先进入线性区。

nieniejun

vaeping123 发表于 2022-3-20 15:23
拉扎维P129页
假设下面的管子M1先进入线性区，Vds减小而Vgs1是不变的，那么Id1会下降。Id1和Id2下降但是Vd1 ...

谢谢！

nieniejun

MustafaSami 发表于 2022-3-20 18:58
M2 will enter the triode region first.

As M2 drain voltage (Vd2=Vout) drops, and its gate voltage ( ...

Thanks for your help!