RE: constants.vams

one comment: if the values of `P_K and/or `P_Q change then
simulation results for all previous Verilog-A models
that use these constants will change. the change does not look to be much,
but `P_K/`P_Q appears in some models as part of an argument to exp(),
which will magnify the effect of the change.

for a diode like current, at -50C with 1 volt across it
the difference in current from the difference in physical constants
is 0.15%. at 27C and 0.8 volt the difference is 0.09%.

these are non-trivial differences. if models have parameters,
these will be have been extracted consistently with the existing `P_
physical constants.

the issue of updating the `P_ values needs to be considered carefully.
do you want all existing models that use these constants to give
different simulation results?

this is the reason I do not use these constants when I define models,
I explicitly define the constants I need as part of a model definition.

colin

-----Original Message-----
From: owner-verilog-ams-devmod@eda.org [mailto:owner-verilog-ams-devmod@eda.org] On Behalf Of Kevin Cameron
Sent: Monday, August 23, 2004 9:19 AM
To: Geoffrey.Coram
Cc: Srikanth Chandrasekaran; VerilogA Device Modeling Reflector; verilog-ams@eda.org
Subject: Re: constants.vams

Geoffrey.Coram wrote:

>Sri -
>I was having a look through the "constants.vams" file listing in the
>AMS LRM and found the following mistakes:
>
>1) M_TWO_PI should end with "93" rather than "52"
>(The 9 is obvious from doubling M_PI; I confirmed this with Abramowitz
>and Stegun.)
>
>2) Planck's constant is listed as P_K, which conflicts with the
>definition of Boltzmann's constant; I believe the macro should be P_H.
>
You could add P_H - removing P_K would probably be a bad idea, and
changing P_K to be something else would be a very bad idea. Maybe
add a comment the P_K will be deprecated.

>3) The definition of P_U0 has extra text on the end, indicating the
>value of (4.0e-7 * `M_PI), but if the file were used as-is, it would
>create a syntax error for the parser.
>
>Also, it appears that the values of P_Q and P_K have been updated by
>NIST since the constants were taken from http:://physics.nist.gov
>
>4) the current value for P_Q is 1.60217653e-19
>(the "53" used to be "462")
>5) the current value for P_K is 1.3806505e-23
>(last digit was 3)
>
>
>At least one Spice-like simulator uses traditional Spice values for
>these constants (P_K = 1.3806226e-23), so these last two aren't
>critical.
>
>Do you think (2) and (3) should be fixed in LRM 2.2?
>
>
If the constant definitions are wrong I would certainly vote for fixing
them ASAP.

Kev.

>-Geoffrey
>
>
Received on Mon Aug 23 10:17:59 2004