I have a question about the small signal model of MOSFET. As you know there is a voltage-controlled current source in the model , I've seen somewhere in books that we can replace it with a resistor with r=1/gm and the cause they provide for that, was since the voltage across current source is VGS and the current is gmVgs we can replace it with v/i = vgs/gmvgs =1/gm resistor, now my question is how we say the voltage across current source is vgs since only 1 pin of it is common with VGS and another one is connected to Drain. The voltage of the current source is a little ambiguous for me.

I have a question about the small signal model of MOSFET. As you know there is a voltage-controlled current source in the model. I've seen somewhere in books that we can replace it with a resistor with r=1/gm and the cause they provide for that, was since the voltage across current source is VGS and the current is gmVgs we can replace it with v/i = vgs/gmvgs =1/gm resistor.

How we say the voltage across current source is vgs since only 1 pin of it is common with VGS and another one is connected to the drain? The voltage of the current source is a little ambiguous for me.