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Simulators >> Circuit Simulators >> Negative cbb for BSIM4
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Message started by taik on Jul 1^st, 2011, 7:05am

Title: Negative cbb for BSIM4
Post by taik on Jul 1^st, 2011, 7:05am

Hi,

We are currently having problem with transient convergence on a particular circuit.

Checking with the developer reveals that certain transistors in the circuit had negative cbb which causes this convergence issue.

They are now trying to get us to confirm that this cbb parameter cannot be a negative value.

Anyone has any idea on this?

Thank you in advance.

Title: Re: Negative cbb for BSIM4
Post by Geoffrey_Coram on Jul 8^th, 2011, 5:58am

The BSIM models are known to have problems with transcapacitances like the intrinsic (channel) Cbs. I don't recall ever seeing an example where Cbb was negative; usually, I would expect the junction capacitances to dominate over the channel capacitances.