The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Modeling >> Semiconductor Devices >> A strange result
https://designers-guide.org/forum/YaBB.pl?num=1333489524

Message started by sos on Apr 3^rd, 2012, 2:45pm

Title: A strange result
Post by sos on Apr 3^rd, 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

Title: Re: A strange result
Post by aaron_do on Apr 3^rd, 2012, 5:48pm

Hi,

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

cheers,
Aaron

Title: Re: A strange result
Post by sos on Apr 3^rd, 2012, 6:05pm

aaron_do wrote on Apr 3^rd, 2012, 5:48pm:

Hi,

have you accounted for the bulk transconductance, g_mb? 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