sos
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These simple circuits are giving me strange results, and I suspect it is either a model or simulator issue. It doesn't make sense to me physically.
With the left circuit, a signal of 0 dB is applied at source1. The resulting signal at drain1 is +1.62 dB. This diode has gain.
In the right hand circuit, a signal of 0 dB is applied at gate2. It is attenuated to -1.56 dB at source23. It is then gained back up to -0.063 dB at drain3. Neither the attenuation or the gain make sense here.
I was ready to blame convergence until I found the same results with a small sin wave in transient.
Now connect the bulk to the source on each fet. Both the gain and attenuation go away. About 0 dB throughout the signal path.
The model used is BSIM3.3. The software is Silvaco SmartSpice 4.1.18.R
Thanks, Steve
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