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Non-linear model for SPICE
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wombat
electronics forum beginner


Joined: 12 Feb 2005
Posts: 4

PostPosted: Fri Jul 14, 2006 9:44 am    Post subject: Non-linear model for SPICE Reply with quote

Hi All,

I need to create a resistor whose resistance varies according to an
equation with the variables of the top and bottom voltage (ie. the
voltage across it). I use Altium (was Protel) but I suspect the
fundamental process is the same. My main concern is that it is what
excel would refer to as a circular reference but I don't understand the
inner workings of SPICE tools to know whether it's feasible.

Cheers,
wombat
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Jim Thompson
electronics forum Guru


Joined: 06 May 2005
Posts: 5440

PostPosted: Fri Jul 14, 2006 5:11 pm    Post subject: Re: Non-linear model for SPICE Reply with quote

On Fri, 14 Jul 2006 11:47:55 +0200, wombat
<wombat@flashmail_removethis.com> wrote:

Quote:
Hi All,

I need to create a resistor whose resistance varies according to an
equation with the variables of the top and bottom voltage (ie. the
voltage across it). I use Altium (was Protel) but I suspect the
fundamental process is the same. My main concern is that it is what
excel would refer to as a circular reference but I don't understand the
inner workings of SPICE tools to know whether it's feasible.

Cheers,
wombat

In PSpice this is done with behavioral models, for example "GVALUE",
which is a current source written as an equation relating to the end
voltages.

In other Spice's I believe these are called "B" sources.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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Kevin Aylward
electronics forum Guru


Joined: 03 May 2005
Posts: 329

PostPosted: Sat Jul 15, 2006 7:35 am    Post subject: Re: Non-linear model for SPICE Reply with quote

wombat wrote:
Quote:
Hi All,

I need to create a resistor whose resistance varies according to an
equation with the variables of the top and bottom voltage (ie. the
voltage across it). I use Altium (was Protel) but I suspect the
fundamental process is the same. My main concern is that it is what
excel would refer to as a circular reference but I don't understand
the inner workings of SPICE tools to know whether it's feasible.


In generic spice you use the "B Source".

e.g

b1 1 0 i=2.4*V(1,0) + 3.5*V(1,0)*V(1,0)*

This makes the current through nodes 1,0 be a function of the voltage
across it, i.e. a non-linear resister.

You should make a .subckt model with all the details in it etc...read
manual etc..

Kevin Aylward B.Sc.
431infoEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"There are none more ignorant and useless,than they that seek answers
on their knees, with their eyes closed"
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