Re: Why is limexp() an analog operator.

limexp is an exponential (analog operator) clamped to linear extrapolation for large values.. 
I've never heard of pnjlim (not a spice user ,nor compact model developer) 
the point of limexp is to provide an exp that would NOT lead to convergence issues in an analog solver.. (assumed to be spice like)
in NON-analog contexts one would just use exp , as its the desired function, and there is no convergence issue to avoid.. 

the point of limexp is NOT linear extrapolation (we have table model and other ways to do that.) its just an exponential "limited" to a linear function for large input values.
Jonathan


 
Jonathan David
j.david@ieee.org
jb_david@yahoo.com
http://ieee-jbdavid.blogspot.com
Mobile 408 390 2425
Work:
jbdavid@scintera.com
http://www.scintera.com
408 636-2618

----- Original Message ----
From: Geoffrey.Coram <geoffrey.coram@analog.com>
To: David Miller <David.L.Miller@freescale.com>
Cc: Verilog-AMS LRM Committee <verilog-ams@eda.org>
Sent: Wednesday, October 10, 2007 8:05:02 AM
Subject: Re: Why is limexp() an analog operator.

The old spice pnjlim is still a powerful tool!

If you want linear extrapolation, then you can write your own
analog function to do that, and then you can use the function
wherever you want.

In my experience, pnjlim is better.

-Geoffrey


David Miller wrote:
> I am wondering why we treat limexp() as an analog operator? Do we really 
> need to store previous history of limexp() (My understanding is this is 
> what the old SPICE pnjlim does.)
> Can't we just perform a linear extrapolation when the input goes out of 
> bounds?
> Having limexp() as an analog operator imposes lots of restrictions on 
> where it can be used.
> 
> Dave

-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.





-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.