a) AM=? (when Cgs and Cgd are 0) --> AM = -gmRL / (1+gmRs)
b) ωH=? (using OCTC method)
Rgs =? Rgd=?
I'm stacked on this point.
In the case of CS MOSFET without Rs:
Rgs=Rsig
Rgd= Rsig(1+gmRL)+RL

What will change in CS MOSFET with Rs?

I'd really appreciate any help. Thanks in advance.

 

You need to solve this circuit



If you whant to find Rgs seen by Cgs capacitor.

Rgs = Vx/Ix

Also notice that now Vgs = Vx and Is = Id - Ix.

Can you solve it ?


As for Rgd resistance seen by Cgd capacitor, you need to solve this circuit:



And once again

Rgd = Vx/Ix

 

You need to solve this circuit

View attachment 152969

If you whant to find Rgs seen by Cgs capacitor.

Rgs = Vx/Ix

Also notice that now Vgs = Vx and Is = Id - Ix.

Can you solve it ?

Vx = IxRsig - (gmVgs - Ix)Rs
Vx(1+gmRs) = Ix(Rsig + Rs)

=> Rgs = Vx/Ix = (Rsig + Rs) / (1 + gmRs)

As for Rgd resistance seen by Cgd capacitor, you need to solve this circuit:

View attachment 152978

And once again

Rgd = Vx/Ix

VG = Vgs + gmVgsRs
VG = IxRsig
Vgs = IxRsig / (1+gmRs)

Vx= VG -VD=IxRsig - (-IDRD) = IxRsig + (Ix + gmVgs)RD = Ix(Rsig + RD) + gmVgsRD
Vx / Ix = Rsig + RD + gmVgsRD / Ix

=> Rgd = Rsig + RD + gmRsigRD / (1 + gmRs) = Rsig + RD ( 1 + gmRsig / 1+gmRs )


Thanks a lot. I find it really helpful.