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Compact model numerical precision (Read 843 times)

A_Programmer Junior Member Offline Posts: 13	Compact model numerical precision Jul 07^th, 2006, 2:03am I have just implemented a compact model in Verilog A. But comparing with the original model implemented in Spice, there are some differences between their simulation results. Provided that I have eliminated all the logical errors. What are the possible sources of error? Can numberical precision harm me in this case? Thanks a lot.
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Geoffrey_Coram

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Re: Compact model numerical precision
Reply #1 - Jul 7^th, 2006, 7:23am

My first guess would be that your physical constants are off.

Spice uses some old values for q (electron charge) and k (Boltzmann's constant), whereas the Verilog-AMS LRM specifies values from NIST. Unfortunately, the NIST values keep changing as those darn physicists get better at measuring these things. Colin McAndrew points out that this is a *terrible* thing for compact modeling; you want to fix a value for q so that the circuit simulator matches the device parameter extraction tool.

-Geoffrey

If at first you do succeed, STOP, raise your standards, and stop wasting your time.

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A_Programmer Junior Member Offline Posts: 13	Re: Compact model numerical precision Reply #2 - Jul 7^th, 2006, 11:04pm Thanks a lot Geoffrey. Do you mean that I should add: `define q 1.6e-19 in my verilog code?
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Geoffrey_Coram

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Re: Compact model numerical precision
Reply #3 - Jul 10^th, 2006, 4:10am

A_Programmer wrote on Jul 7^th, 2006, 11:04pm:

Thanks a lot Geoffrey. Do you mean that I should add:

`define q 1.6e-19

in my verilog code?

Yikes! No, you should have a few digits more. Right now, the AMS LRM says
`define P_Q 1.602176462e-19

whereas BSIM3 has hard-coded
#define Charge_q 1.60219e-19

You can try that value, or you can try to find the actual value used in Spice, if you have the source code.

If at first you do succeed, STOP, raise your standards, and stop wasting your time.

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