HI,
Please, I am going to design current mirror using MOSFET transistor,
how can I choose the dimensions of the transistors to get high impedance (ro for the transistor) of the current source without channel length modulation.
how can I choose the dimensions of the transistors to get high impedance (ro for the transistor) of the current source without channel length modulation.
You can't. Transistor dimensioning is a matter of different trade-offs. You can reduce (not eliminate !) channel length modulation by increasing L, need to also increase W to keep gm and Idss which in turn increases output capacitance. Channel modulation induced ro can be cancelled by using cascode topology, as mentioned in your previous thread, at higher voltage drop cost. Presume the topic is discussed in detail in your favorite IC design text book.
Thank you for your reply,
Yes of course I want to design a current source with high output impedance, this is what I want. But how?
I am asking about the sizing of the transistors in the current source how much W and L?
You can't. Transistor dimensioning is a matter of different trade-offs. You can reduce (not eliminate !) channel length modulation by increasing L, need to also increase W to keep gm and Idss which in turn increases output capacitance. Channel modulation induced ro can be cancelled by using cascode topology, as mentioned in your previous thread, at higher voltage drop cost. Presume the topic is discussed in detail in your favorite IC design text book.
I cannot use cascode (I don't need voltage drop loss).
My question is how can I choose the size of W and L for the current source (current mirror) to keep ro high with (1mA) without affecting channel length modulation?
Please, can you mention a good textbook for designs like these circuits and choosing the dimensions of the transistors?