darkk
Member level 3
Hi, folks
Here I bring up a quite simple question, but I'm a little lost.
Attached is the schematic of the pmos current mirror consisting of M1 and M2. The common practice is to put a capacitor C between the power supply and the gates of M1/2. My question is that what the capacitor C does for?
1. removing the AC noise coupling to the gates of M1 and M2.
OK, that sounds good. BUT how about I connects the cap C between the gates and gnd. Also it can do the same thing, right?
2. Someone will say that inserting the cap between power supply and the gates can improve the PSRR by keeping the Vgs of the transistors somehow constant.
OK, if you argue this way, I can think that without the capacitor C the Vgs of M1 also can sort of be kept constant if the current source is good.
So I come to the dilemma: Can I just connect the cap either to ground or power supply??
Here I bring up a quite simple question, but I'm a little lost.
Attached is the schematic of the pmos current mirror consisting of M1 and M2. The common practice is to put a capacitor C between the power supply and the gates of M1/2. My question is that what the capacitor C does for?
1. removing the AC noise coupling to the gates of M1 and M2.
OK, that sounds good. BUT how about I connects the cap C between the gates and gnd. Also it can do the same thing, right?
2. Someone will say that inserting the cap between power supply and the gates can improve the PSRR by keeping the Vgs of the transistors somehow constant.
OK, if you argue this way, I can think that without the capacitor C the Vgs of M1 also can sort of be kept constant if the current source is good.
So I come to the dilemma: Can I just connect the cap either to ground or power supply??