Calculate transfer function of transconductance amplifier circuit
The open Loop gain and transfer function of the MOSFET can be neglected if you follow basic rules for DC bias.


for (RdsON+R1)*Iout &lt; Vo &lt; Vcc   (Vo is current sink voltage)
for Vgs>Vth   for gate threshold Vth
OpAmp-out swings from Vgs (+Iout*R1) to above Vcc (by Vgs)
for R1 &lt;&lt; RdsOn to give more gain and voltage swing on MOSFET
for Vin=0 to Vmax ( AC with DC offset=Vpk)


Then you get full supply range swing for Iout


limited only by your power source and Op Amp swing to drive gate and RdsOn and heat sink to dissipate Vds*Iout



  Iout = Vin / R1  and has nothing to do with Av, RdsOn, Vth etc.



however bandwidth will depend on GBW of OA.