DC analysis in Cadence

[elbadry]

When doing DC-analysis in cadence (IC5033) and printing the dc operating points, I find that some of the given capacitance values are negative. What does this mean?

and where can I find the description of the too many capacitances given by the dc-analysis?

thanks in advance

 

[eng_Semi]

from the EDA window choose results --> print --> then choose the transistor u want

Best regards

 

[BigBoss]

Which model do you use ?? DC analysis may give some capacitance values depending on bias but these should not be negative..
If so, the is a problem of modelling.

In additional to, first versions of 5.033 may have some bugs that computes some parameters of a active device. Because evolution period of 5.033 isn't finished.

 

[elbadry]

I am using (Austria-micro-systems) 0.35um BiCMOS design Kit...Could the problem be in their models? If so, is their a way out?

 

[BigBoss]

I am using (Austria-micro-systems) 0.35um BiCMOS design Kit...Could the problem be in their models? If so, is their a way out?

If a capacitance value is negative, it means that is an inductance !! It's so weird...??

In additional to, some design kits need some corrective verilog scripts ( for instance, for Bf there may be Gauss equation that creates a possibility variations etc..) Cadence interprets first them and then computes the equations.

I think the your design kit has some bugs...

One last point :Some parameters which start with C could not be a capacitor, they might be an internal variables...

 

[elbadry]

One last point :Some parameters which start with C could not be a capacitor, they might be an internal variables...

Could you please give more details? How can i know if these are Caps or not?
Thanks for help

 

[huojinsi]

"Capacitance value is negative",maybe your model is not correct!

 

[nkchenliy]

Yes, huojinsi is right. Your model is not correct!

 

[layes2]

not dc you should use ac to get cap

 

[cristianb]

the models are corect.I've seen these negative cap values in several design kits.

 

[qutang]

I think is the initial problem.

 

[rfsystem]

BSIM3v3 models show negative cap values over the operating range. The default setup of CDS only show CGS, CDS, CDG ... . The negative caps are only seen in result text file which show more details.

 

[victoriya]

i think getting the negative capacitance is because of the direction of the current and the variation of q.that causes the negative sign in derivetive equation.

 

[dgnani]

This post was from 2005...