that's the original circuitHow to find Vo of this pi model of FET amplifier? enter image description here I have to find voltage amplification (Av=Vo/Vi) of this circuit and output resistance Ro, so I need to find the Vo voltage. I found the expression for current id, but I don't know how to express Vo. Could you please help? Thanks in advance.

(id-gm1Vgs1)rd1 + idRs1 + (id-gm2Vgs2)rd2 + idRs2=0

(id -gm1(Vi-idRs1))rd1 + idRs1 + (id-gm2(Vi-idRs2))rd2 +idRs2=0

if the calculation are made

id= (gm1rd1 +gm2rd2)Vi / rd1+rd2+Rs1+Rs2+gm1Rs1rd1+gm2Rs2rd2

this is the original circuit

that's the original circuit


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Please show us what you have done so far \$\endgroup\$ – DerStrom8 Jan 25 '18 at 20:54
  • \$\begingroup\$ @DerStrom8 I edited the post \$\endgroup\$ – greenland Jan 25 '18 at 21:11
  • \$\begingroup\$ Are you sure both transistors are PMOS transistors? I have a small hunch that M2 needs to be an NMOS transistor, else the bulk-source PN junction will start conducting. \$\endgroup\$ – Sven B Jan 26 '18 at 8:31
  • \$\begingroup\$ Also, I believe that in your small-signal equivalent circuit, your transconductance \$g_{m1}V_{gs1}\$ is pointed the wrong way. \$\endgroup\$ – Sven B Jan 26 '18 at 8:44
  • \$\begingroup\$ @SvenB I uploaded the original circuit, too. Indeed, I am not clear if the transistors are NMOS or PMOS. Shouldn't gm1Vgs1 be directed from drain to source? \$\endgroup\$ – greenland Jan 28 '18 at 17:45

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