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PHY_RES SPECTRE (Read 10414 times)
monte78
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PHY_RES SPECTRE
Aug 13th, 2008, 9:40am
 
Hello everybody,


I have a question about the phy_res model in spectre. I am designing a resistive DAC using n-diffusion resistors, but I am seeing some problems about the non-linear voltage dependence of these resistors.

In particular I noticed that the problem is due to the fact that the behaviour of the resistor is asymmetric with respect to the terminals Vt1 and Vt2, in the sense that if I put the resistors in one way I obtain a certain INL, while putting them in the opposite way the INL change (the resistor is perfectly symmetric from a layout point of view).

This is obviously a non-sense, so my questions are:

1) Can I use the phy_res model in the case that I am not sure about the more negative terminal of the resistor?
2) Why the phy_res model doesn't take into account the absolute value of the voltage across it? (polyarg=diff)
3) Is there a possibility to have the absolute value take into account on these resistors?

Thanks, Best Regards,

Monte
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Geoffrey_Coram
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Re: PHY_RES SPECTRE
Reply #1 - Aug 13th, 2008, 10:45am
 
Isn't this a question for the foundry modeling team?  polyarg=diff gives them the ability to make a symmetric device, and they chose not to!
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monte78
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Re: PHY_RES SPECTRE
Reply #2 - Aug 14th, 2008, 1:11am
 
Hi,

The problem is the polyarg=diff! If I have the plus terminal more negative than the minus terminal the model is not correct.  :(

Geoffrey_Coram wrote on Aug 13th, 2008, 10:45am:
Isn't this a question for the foundry modeling team?  polyarg=diff gives them the ability to make a symmetric device, and they chose not to!

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Geoffrey_Coram
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Re: PHY_RES SPECTRE
Reply #3 - Aug 15th, 2008, 11:17am
 
Hmm, I read the Spectre documentation that said that the resistor is symmetric wrt the two resistor terminals when polyarg=diff.  It's when polyarg=sum that you get asymmetry.

However, now that I look at the equation, it's only symmetric if the odd coefficients are zero, since there's no absolute value for V = V(t1) - V(t2).
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monte78
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Re: PHY_RES SPECTRE
Reply #4 - Aug 20th, 2008, 5:58am
 
You are right, this is basically my problem. I will change model!

Thanks, Bye,

Monte

Geoffrey_Coram wrote on Aug 15th, 2008, 11:17am:
Hmm, I read the Spectre documentation that said that the resistor is symmetric wrt the two resistor terminals when polyarg=diff.  It's when polyarg=sum that you get asymmetry.

However, now that I look at the equation, it's only symmetric if the odd coefficients are zero, since there's no absolute value for V = V(t1) - V(t2).

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jbdavid
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Re: PHY_RES SPECTRE
Reply #5 - Aug 27th, 2008, 1:23am
 
for a diffusion resistor, the Phillips RDIFF model is probably a good bit better than the phy_res..

I think its built into spectre (and spice) these days..
If _I_ had to create a diffusion resistor model for a pdk, its what I'd use.
G'luck
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jbdavid
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sheldon
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Re: PHY_RES SPECTRE
Reply #6 - Sep 13th, 2008, 5:57am
 
You might also want to look at r3, the Compact Modeling Council
three terminal resistor model. It has also available and intended
for modeling the non-linearity of three terminal resistors.

                                                      Best Regards,

                                                        Sheldon
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rf-design
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Re: PHY_RES SPECTRE
Reply #7 - Mar 29th, 2009, 5:42am
 
I read the McAndrew paper.

Is the "r3" which implement depletion, velocity and self heating somewhere implemented?
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Geoffrey_Coram
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Re: PHY_RES SPECTRE
Reply #8 - Aug 11th, 2009, 10:09am
 
The r3 model was standardized by the Compact Model Council; it's available in recent versions of Spectre, and I believe the Verilog-A is available from the CMC web site.
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