kirchom matrix parameter question

[yefj]

Hello, in the expression shown bellow it is assumed to be for Vout=0 so if we put Vout=0 then we have GND on out so there is no Iout

Hown did they get the expression shown bellow ( A)?

Thanks.

 

[BigBoss]

Being of Vout=0 does not require Iout=0..

 

[FvM]

It took me some time to realize that capital S in your formula actually means lower case s respectively jω.

It's ok to draw Vout=0 as a short, but then Iout is the current through this short and the current source should be omitted.

The simple meaning of this setup is: You are shorting the source follower output, inject a current to the input and observe the generated output current. Part of the putput current is directly fed through Cgs (the "1" term) the other part is generated by the FET conductance (the gm/sCgs term). The expression is correct under the assumption Cgd << Cgs.

 

[yefj]

Hello,Yes i got the logic of the expression when Vout=0.

Could you please help me with the logic when I_in=0 expression signed as I_22 and B?
When Iin=0 then there is no voltge drop on Cgs so Vgs=0 and gm*Vgs=0
So we left with only I_out current flowing to source RS||R0 so Vout=I_out*RS||R0
They say that I22=GL+g0 ,cant see why?

The same thing goes for expression B=Vin/Vout for I_in=0
if I_in is zero then how could we measure Vin at all?
Thanks