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A strange result (Read 3415 times)
sos
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A strange result
Apr 03rd, 2012, 2:45pm
 
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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aaron_do
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Re: A strange result
Reply #1 - Apr 3rd, 2012, 5:48pm
 
Hi,


have you accounted for the bulk transconductance, gmb? If so, why don't you think this is the reason?


cheers,
Aaron
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there is no energy in matter other than that received from the environment - Nikola Tesla
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sos
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Re: A strange result
Reply #2 - Apr 3rd, 2012, 6:05pm
 
aaron_do wrote on Apr 3rd, 2012, 5:48pm:
Hi,


have you accounted for the bulk transconductance, gmb? If so, why don't you think this is the reason?


cheers,
Aaron


Thank you Aaron, that fits. I'm a bipolar designer; it didn't occur to me the bulk terminal could have gain.

Steve
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