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I wanted to use a BSIM4 model of NMOS in my circuit. I got the correct dc biasing point, certain VDS,VGS and IC. But I am having issues measuring S-parameter data for MOSFET amplifiers. I simulated circuits in BJT and it works fine. Is there any generic circuit for MOSFET? I am not sure where to put up the DC block and RF feed with proper biasing in MOSFET (NMOS)so that S-parameter data could be measured. I ended up with the circuit shown below, it has invalid data for S-paramters if measured. Any suggestion/correction in the circuitry will be very much helpful.

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I am getting the S21 (dB) is below, which is invalid:

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My bias points are VDS=0.5V, VGS=0.8V, IDS=45.48uA and supply VDD=1.2V. Hence I got RDS(which is R1)=15.39kohms.

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    \$\begingroup\$ You were successful with the BJT circuit, show that circuit so we can suggest how to adapt it for a MOSFET. Your input signal goes through the DC blocker and then ends up at SRC1 which is an ideal DC voltage source to ground. How much signal can exist across such a source? \$\endgroup\$ – Bimpelrekkie Sep 10 '18 at 18:43
  • \$\begingroup\$ Thank you. I added the RF choke inductor and it worked! missed to see an extra path in the circuit. Will add the short answer. \$\endgroup\$ – sundar Sep 10 '18 at 20:16
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The credit of the answer goes to @Bimpelrekkie.

Adding an extra RF choke inductor solved the issue.

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