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spModels.hlp
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!! ---------------------------------------------------------------
!! Xic/WRspice Help System Database
!! $Id: spModels.hlp,v 1.36 2016/10/16 19:25:43 stevew Exp $
!! Copyright (C) Whiteley Research Inc. 2003. All Rights Reserved
!! ---------------------------------------------------------------
!!TAG WRspice
!! This file in sync with manual.
!!KEYWORD
spModels.hlp
!!TITLE
spModels.hlp
!!HTML
!!SUBTOPICS
.model
.defmod
temperature
capmodel
indmodel
resmodel
swmodel
tramodel
urcmodel
diomodel
bjtmodel
jfetmodel
mesmodel
moslevel
mosmodel
jjmodel
!! elements.tex 071918
!!KEYWORD
.model
!!TITLE
Device Models
!!HTML
Many devices reference models, which contain values for the
numerous parameters describing the device, which would be
cumbersome to include in each device reference. Device models are
specified on a <tt>.model</tt> line. The model can be referenced
by any number of devices of the corresponding type.
<p>
General form:
<blockquote>
<tt>.model</tt> <i>modname type</i> (<i>pname1=pval1</i>
<i>pname2=pval2</i> ... )
</blockquote>
<p>
Examples:
<blockquote><tt>
.model mod1 npn (bf=50 is=1e-13 vbf=50)<br>
.model interconnect ltra (r=0.2 l=9.13nh c=3.65pf
len=5 rel=.002 compactrel=1.0E-4)<br>
</tt></blockquote>
<p>
The <tt>.model</tt> line specifies a set of model parameters that
will be used by one or more devices. The <i>modname</i> is the
model name, which is case insensitive in matching references, and
<tt>type</tt> is one of the following types:
<blockquote>
<table border=1 cellpadding=2 bgcolor="#ffffee">
<tr><td><a href="capmodel"><tt>c</tt></a></td>
<td>Capacitor model</td></tr>
<tr><td><a href="indmodel"><tt>l</tt></a></td>
<td>Inductor model</td></tr>
<tr><td><a href="resmodel"><tt>r</tt></a></td>
<td>Resistor model</td></tr>
<tr><td><a href="swmodel"><tt>sw</tt></a></td>
<td>Voltage-controlled switch</td></tr>
<tr><td><a href="swmodel"><tt>csw</tt></a></td>
<td>Current-controlled switch</td></tr>
<tr><td><a href="ltramodel"><tt>tra</tt></a></td>
<td>General transmission line model</td></tr>
<tr><td><a href="ltramodel"><tt>ltra</tt></a></td>
<td>Lossy transmission line model</td></tr>
<tr><td><a href="urcmodel"><tt>urc</tt></a></td>
<td>Uniform RC line model</td></tr>
<tr><td><a href="diomodel"><tt>d</tt></a></td>
<td>Diode model</td></tr>
<tr><td><a href="bjtmodel"><tt>npn</tt></a></td>
<td>NPN BJT model</td></tr>
<tr><td><a href="bjtmodel"><tt>pnp</tt></a></td>
<td>PNP BJT model</td></tr>
<tr><td><a href="jfetmodel"><tt>njf</tt></a></td>
<td>N-channel JFET model</td></tr>
<tr><td><a href="jfetmodel"><tt>pjf</tt></a></td>
<td>P-channel JFET model</td></tr>
<tr><td><a href="mesmodel"><tt>nmf</tt></a></td>
<td>N-channel MESFET model</td></tr>
<tr><td><a href="mesmodel"><tt>pmf</tt></a></td>
<td>P-channel MESFET model</td></tr>
<tr><td><a href="mosmodel"><tt>nmos</tt></a></td>
<td>N-channel MOSFET model</td></tr>
<tr><td><a href="mosmodel"><tt>pmos</tt></a></td>
<td>P-channel MOSFET model</td></tr>
<tr><td><a href="jjmodel"><tt>jj</tt></a></td>
<td>Josephson junction model</td></tr>
</table>
</blockquote>
<p>
Parameter values are defined by appending the parameter name, as
given for each model type, followed by an equal sign and the
parameter value. Model parameters that are not given a value are
generally assigned default values.
<p>
The <a href="show"><b>show</b></a> command with the <tt>-M</tt>
option is useful for listing the parameters that can be specified
to a model. Only the parameters not listed as "<tt>RO</tt>"
(read-only) can appear in a <tt>.model</tt> line.
<p>
<a name="units">
In the tables found in the subtopics, the various model parameters
are listed. The <b>units</b> field of the tables provides the
assumed units of measure for the parameter, which is expressed
using symbols from the following table.
</a>
<blockquote>
<table border=1 cellpadding=2 bgcolor="#ffffee">
<tr><td> M </td><td> meters </td></tr>
<tr><td> cM </td><td> centimeters </td></tr>
<tr><td> µM </td><td> microns </td></tr>
<tr><td> S </td><td> seconds </td></tr>
<tr><td> Hz </td><td> hertz </td></tr>
<tr><td> F </td><td> farads </td></tr>
<tr><td> H </td><td> henries </td></tr>
<tr><td> O </td><td> ohms </td></tr>
<tr><td> C </td><td> degrees Celsius </td></tr>
<tr><td> sq </td><td> square </td></tr>
<tr><td> A </td><td> amperes </td></tr>
<tr><td> V </td><td> volts </td></tr>
<tr><td> eV </td><td> electron-volts </td></tr>
<tr><td> deg </td><td> degrees </td></tr>
</table>
</blockquote>
<p>
The resistor and smeiconductor models include <a
href="temperature">temperature</a> dependence.
!!SEEALSO
spinput
.defmod
!! elements.tex 072018
!!KEYWORD
.defmod
!!TITLE
Default Models
!!HTML
Some simple devices support a "default model" in <i>WRspice</i>,
meaning that if no model name is given in an instance line, an
internally provided default model will be used. Internally, all
devices have a model structure, which is a container for the
instances of that device type. It is possible to access the
default model used for various devices with <tt>.defmod</tt>
lines. This will affect all devices of the corresponding type
that are not explicitly given a model in the instantiation line.
<p>
General form:
<blockquote>
<tt>.defmod</tt> <i>type</i> (<i>pname1=pval1</i>
<i>pname2=pval2</i> ... )
</blockquote>
<p>
Examples:
<blockquote><tt>
.defmod r (m=1.2)<br>
.defmod c (temp=300 tc1=.002)
</tt></blockquote>
<p>
The <i>type</i> is the name of the device model (the second name
that would be provided on a <a href=".model"><tt>.model</tt></a>
line) such as <tt>R</tt> (for resistors), <tt>C</tt> (for
capacitors), and <tt>L</tt> (for inductors).
<p>
The type name is followed by a list of parameter assignments,
optionally enclosed in parentheses. These are precisely the same
as would appear in a <tt>.model</tt> line for the device. These
provide the values for the parameters to be used in the default
model.
<p>
Not all devices support default models, meaning that lack of a
model name in an instance line is an error. In particular devices
that have a variable terminal count (optional nodes) require a
model name and therefor don't support a default model.
<p>
It is probably also not possible to use a <tt>level</tt>
parameter in a default model, and binning parameters will be
ignored at best. Anything too fancy should be done through a
normal model, or there may be trouble.
<p>
The capability is very powerful, but might cause headaches, too,
so the user should beware. For example, if the following line is
added to an existing deck
<blockquote>
<tt>.defmod R(M=1.2)</tt>
</blockquote>
all "standard" resistors in the deck will have their values
reduced by about twenty percent. This can be useful for corner
analysis, but don't let the line get "lost" in a big file.
!!SEEALSO
spinput
!! elements.tex 091511
!!KEYWORD
temperature
!!TITLE
Analysis at Different Temperatures
!!HTML
All input data for <i>WRspice</i> is assumed to have been measured
at a nominal temperature of 25C, which can be changed by use of
the <a href="tnom"><tt>tnom</tt></a> parameter on the <a
href=".options"><tt>.options</tt></a> control line. Note that
this is the same default temperature used in <a
href="hspicesim">HSPICE</a>, but is not the same as in Berkeley
SPICE3 or in <i>WRspice</i> releases prior to 3.2.15, which was
27C.
<p>
This value can further be overridden for any device which models
temperature effects by specifying the <tt>tnom</tt> parameter on
the model itself. The circuit simulation is performed at a
temperature of 25C unless overridden by a <a
href="temp"><tt>temp</tt></a> parameter on the <tt>.options</tt>
control line. Individual device instances may further override
the circuit temperature through the specification of a
<tt>temp</tt> parameter on the instance.
<p>
Temperature dependent support is provided for resistors and
semiconductor devices. The details of the temperature adjustments
can be found in the description of the models. For details of the
BSIM temperature adjustment, see <a href="park">Park</a> (BSIM1),
<a href="szeto">Szeto</a> (BSIM2), and <a href="cheng">Cheng</a>
(BSIM3).
<p>
Temperature appears explicitly in the exponential terms of the BJT
and diode model equations. In addition, saturation currents have
a built-in temperature dependence. The temperature dependence of
the saturation current in the BJT models is determined by:
<blockquote>
<i>I</i><sub>s</sub>(<i>T</i><sub>1</sub>) =
<i>I</i><sub>s</sub>(<i>T</i><sub>0</sub>)
(<i>T</i><sub>1</sub>/<i>T</i><sub>0</sub>)<sup><i>XTI</i></sup>
exp( <i>E</i><sub>g</sub><i>q</i>(<i>T</i><sub>1</sub> -
<i>T</i><sub>0</sub>) /
<i>k</i><i>T</i><sub>1</sub><i>T</i><sub>0</sub> )
</blockquote>
where <i>k</i> is Boltzmann's constant, <i>q</i> is the electronic
charge, <i>E</i><sub>g</sub> is the energy gap which is a model
parameter, and <i>XTI</i> is the saturation current temperature
exponent (also a model parameter, and usually equal to 3).
<p>
The temperature dependence of forward and reverse beta is according to
the formula:
<blockquote>
<i<B</i>(<i>T</i><sub>1</sub>) = <i<B</i>(<i>T</i><sub>0</sub>)
(<i>T</i><sub>1</sub>/<i>T</i><sub>0</sub>)<sup><i>XTB</i></sup>
</blockquote>
<p>
where <i>T</i><sub>1</sub> and <i>T</i><sub>0</sub> are in Kelvin,
and <i>XTB</i> is a user-supplied model parameter. Temperature
effects on beta are carried out by appropriate adjustment to the
values of <i>B</i><sub>F</sub>, <i>I</i><sub>SE</sub>,
<i>B</i><sub>R</sub>, and <i>I</i><sub>SC</sub> (<i>WRspice</i>
model parameters <tt>bf</tt>, <tt>ise</tt>, <tt>br</tt>, and
<tt>isc</tt>, respectively).
<p>
Temperature dependence of the saturation current in the junction
diode model is determined by:
<blockquote>
<i>I</i><sub>s</sub>(<i>T</i><sub>1</sub>) =
<i>I</i><sub>s</sub>(<i>T</i><sub>0</sub>)
(<i>T</i><sub>1</sub>/<i>T</i><sub>0</sub>)<sup><i>XTI</i>/<i>N</i></sup>
exp( <i>E</i><sub>g</sub><i>q</i>(<i>T</i><sub>1</sub> -
<i>T</i><sub>0</sub>) /
<i>Nk</i><i>T</i><sub>1</sub><i>T</i><sub>0</sub> )
</blockquote>
<p>
where <i>N</i> is the emission coefficient, which is a model
parameter, and the other symbols have the same meaning as above.
Note that for Schottky barrier diodes, the value of the saturation
current temperature exponent, <i>XTI</i>, is usually 2.
<p>
Temperature appears explicitly in the value of junction potential,
<i>Phi</i> (in <i>WRspice</i>, <tt>phi</tt>), for all device
models. The temperature dependence is determined by:
<blockquote>
<i>Phi</i>(<i>T</i>) = (<i>kT</i>/<i>q</i>)
ln( <i>N</i><sub>a</sub><i>N</i><sub>d</sub> /
<i>N</i><sub>i</sub>(<i>T</i>)<sup>2</sup> )
</blockquote>
where <i>k</i> is Boltzmann's constant, <i>q</i> is the electronic
charge, <i>N</i><sub>a</sub> is the acceptor impurity density,
<i>N</i><sub>d</sub> is the donor impurity density, and
<i>N</i><sub>i</sub> is the intrinsic carrier concentration.
<p>
Temperature appears explicitly in the value of surface mobility,
<i>u</i><sub>0</sub> (or <tt>u0</tt>, for the MOSFET models).
This temperature dependence is determined by:
<blockquote>
<i>u</i><sub>0</sub>(<i>T</i>) =
<i>u</i><sub>0</sub>(<i>T</i><sub>0</sub>) /
(<i>T</i>/<i>T</i><sub>0</sub>)<sup>1.5</sup>
</blockquote>
<p>
The effects of temperature on resistors is modeled by the formula:
<blockquote>
<i>R</i>(<i>T</i>) = <i>R</i>(<i>T</i><sub>0</sub>)[1 +
<i>TC</i><sub>1</sub>(<i>T</i>-<i>T</i><sub>0</sub>) +
<i>TC</i><sub>2</sub>(<i>T</i>-<i>T</i><sub>0</sub>)<sup>2</sup>]
</blockquote>
where <i>T</i> is the circuit temperature, <i>T</i><sub>0</sub> is
the nominal temperature, and <i>TC</i><sub>1</sub> and
<i>TC</i><sub>2</sub> are the first and second-order temperature
coefficients.
!! elements.tex 071918
!!KEYWORD
capmodel
!!TITLE
Capacitor Models
!!HTML
<b>Type Name:</b> <tt>c</tt>
<p>
The <a href="cap">capacitor</a> model contains process information
that may be used to compute the capacitance from strictly
geometric information.
<p>
<table border=1 cellpadding=2 bgcolor="#ffffee">
<tr><th>name</th>
<th>parameter</th>
<th>units</th> <th>default</th> <th>example</th></tr>
<tr><td><tt>m</tt></td>
<td>parallel multiplier</td>
<td>-</td> <td>1.0</td> <td>1.2</td></tr>
<tr><td><tt>cj</tt></td>
<td>junction bottom capacitance</td>
<td>F/M<sup>2</sup></td> <td>-</td> <td>5e-5</td></tr>
<tr><td><tt>cjsw</tt></td>
<td>junction sidewall capacitance</td>
<td>F/M</td> <td>-</td> <td>2e-11</td></tr>
<tr><td><tt>defw</tt></td>
<td>default device width</td>
<td>M</td> <td>1e-6</td> <td>2e-6</td></tr>
<tr><td><tt>narrow</tt></td>
<td>narrowing due to side etching</td>
<td>M</td> <td>0.0</td> <td>1e-7</td></tr>
<tr><td><tt>tnom</tt></td>
<td>parameter measurement temperature</td>
<td>C</td> <td>25</td> <td>50</td></tr>
<tr><td><tt>tc1</tt></td>
<td>first order temperature coeff</td>
<td>O/C</td> <td>0.0</td> <td>-</td></tr>
<tr><td><tt>tc2</tt></td>
<td>second order temperature coeff</td>
<td>O/C<sup>2</sup></td> <td>0.0</td> <td>-</td></tr>
</table>
<p>
The capacitor has a nominal capacitance computed as below, where
<i>l</i> and <i>w</i> are parameters from the device line.
<blockquote>
C = <tt>cj</tt>·(<i>l</i>-<tt>narrow</tt>)·(<i>w</i>-<tt>narrow</tt>)
+   2·<tt>cjsw</tt>·(<i>l</i>+<i>w</i>-2·<tt>narrow</tt>)
</blockquote>
<p>
After the nominal capacitance is calculated, it is adjusted for
temperature by the formula:
<blockquote>
C(temp) = C(<tt>tnom</tt>)·(1 +
<tt>tc1</tt>·(temp-<tt>tnom</tt>) +
<tt>tc2</tt>·(temp-<tt>tnom</tt>)<sup>2</sup>)
</blockquote>
<p>
Finally, the capacitance is multiplied by the parallel
multiplication factor (<tt>m</tt>).
!!SEEALSO
.model
!! elements.tex 071918
!!KEYWORD
indmodel
!!TITLE
Inductor Models
!!HTML
<b>Type Name:</b> <tt>l</tt>
<p>
The <a href="ind">inductor</a> model currently contains only one
parameter. A geometric model may be added in future.
<p>
<table border=1 cellpadding=2 bgcolor="#ffffee">
<tr><th>name</th>
<th>parameter</th>
<th>units</th> <th>default</th> <th>example</th></tr>
<tr><td><tt>m</tt></td>
<td>parallel multiplier</td>
<td>-</td> <td>1.0</td> <td>1.2</td></tr>
</table>
<p>
The parallel multiplier acts on each inductor instance of the model,
dividing the inductance given by this value.
!!SEEALSO
.model
!! elements.tex 071918
!!KEYWORD
resmodel
!!TITLE
Resistor Models
!!HTML
<b>Type Name:</b> <tt>r</tt>
<p>
The <a href="res">resistor</a> model consists of process-related
device data that allow the resistance to be calculated from
geometric information and to be corrected for temperature. The
parameters available (multiple names are aliases) are:
<p>
<table border=1 cellpadding=2 bgcolor="#ffffee">
<caption>Resistor Model Parameters</caption>
<tr><th>name</th>
<th>parameter</th>
<th>units</th> <th>default</th> <th>example</th></tr>
<tr><td><tt>m</tt></td>
<td>parallel multiplier</td>
<td>-</td> <td>1.0</td> <td>1.2</td></tr>
<tr><td><tt>tc1</tt>, <tt>tc</tt>, <tt>tc1r</tt></td>
<td>first order temperature coeff</td>
<td>O/C</td> <td>0.0</td> <td>-</td></tr>
<tr><td><tt>tc2</tt>, <tt>tc2r</tt></td>
<td>second order temperature coeff</td>
<td>O/C<sup>2</sup></td> <td>0.0</td> <td>-</td></tr>
<tr><td><tt>rsh</tt></td>
<td>sheet resistance</td>
<td>O/sq</td> <td>-</td> <td>50</td></tr>
<tr><td><tt>defl</tt>, <tt>l</tt>, <tt>w</tt></td>
<td>default length</td>
<td>M</td> <td>0</td> <td>2e-6</td></tr>
<tr><td><tt>defw</tt>, <tt>w</tt></td>
<td>default width</td>
<td>M</td> <td>0</td> <td>2e-6</td></tr>
<tr><td><tt>dl</tt>, <tt>dlr</tt></td>
<td>length reduction due to etching</td>
<td>M</td> <td>0.0</td> <td>1e-7</td></tr>
<tr><td><tt>narrow</tt>, <tt>dw</tt></td>
<td>narrowing due to side etching</td>
<td>M</td> <td>0.0</td> <td>1e-7</td></tr>
<tr><td><tt>tnom</tt>, <tt>tref</tt></td>
<td>parameter measurement temperature</td>
<td>C</td> <td>25</td> <td>50</td></tr>
<tr><td><tt>temp</tt></td>
<td>default instance temperature</td>
<td>C</td> <td>25</td> <td>50</td></tr>
<tr><td><tt>kf</tt></td>
<td>flicker noise coefficient</td>
<td>-</td> <td>0</td> <td> </td></tr>
<tr><td><tt>af</tt></td>
<td>flicker noise exponent of current</td>
<td>-</td> <td>2</td> <td> </td></tr>
<tr><td><tt>ef</tt></td>
<td>flicker noise exponent of frequency</td>
<td>-</td> <td>1</td> <td> </td></tr>
<tr><td><tt>wf</tt></td>
<td>flicker noise exponent of width</td>
<td>-</td> <td>1</td> <td> </td></tr>
<tr><td><tt>lf</tt></td>
<td>flicker noise exponent of length</td>
<td>-</td> <td>1</td> <td> </td></tr>
<tr><td><tt>noise</tt></td>
<td>noise conductance multiplier</td>
<td>-</td> <td>1</td> <td> </td></tr>
</table>
<p>
The sheet resistance is used with the etch reduction parameters and
<i>l</i> and <i>w</i> from the resistor element line to determine
the nominal resistance by the formula
<blockquote>
R = <tt>rsh</tt>·(<i>l</i> - <tt>dl</tt>)/(<i>w</i> -
<tt>narrow</tt>)</tt>
</blockquote>
<p>
The parameters <tt>defw</tt> and <tt>defl</tt> are used to supply
default values for element <i>w</i> and <tt>l</tt> if not
specified on the device line. A fatal error is produced if the
resistance can't be determined from given parameters.
<p>
After the nominal resistance is calculated, it is adjusted for
temperature by the formula:
<blockquote>
R(temp) = R(<tt>tnom</tt>)·(1 +
<tt>tc1</tt>·(temp-<tt>tnom</tt>) +
<tt>tc2</tt>·(temp-<tt>tnom</tt>)<sup>2</sup>)
</blockquote>
<p>
Finally, the resistance is divided by the parallel multiplier
(<tt>m</tt>) value.
<p>
The flicker noise capability can be used in noise analysis. This
requires that <tt>kf</tt>, <tt>l</tt>, and <tt>w</tt> be
specified. To use, the instance line must reference a model, but
also can have a resistance specified which will override model
calculation of resistance.
<p>
Flicker noise model:
<blockquote>
<i>Noise</i> = <tt>(KF *</tt> <i>I</i><tt>^AF) /
(</tt><i>Leff</i><tt>^LF *</tt> <i>Weff</i><tt>^WF *</tt>
<i>f</i><tt>^EF)</tt>
</blockquote>
<blockquote>
<table border=1 cellpadding=2 bgcolor="#ffffee">
<tr><th>Param</th> <th>Description</th> <th>Units</th></tr>
<tr><td><i>Noise</i></td> <td>Noise spectrum density</td>
<td>A<sup>2</sup>Hz</td></tr>
<tr><td><i>I</i></td> <td>Current</td> <td>A</td></tr>
<tr><td><i>Leff</i></td> <td>Eff length (L-DL)</td> <td>M</td></tr>
<tr><td><i>Weff</i></td> <td>Eff width (W-DW)</td> <td>M</td></tr>
<tr><td><i>f</i></td> <td>Frequency</td> <td>Hz</td></tr>
<tr><th>Param</th> <th>Description</th> <th>Default, Range</th></tr>
<tr><td><tt>KF</tt></td> <td>Flicker noise coefficient</td>
<td>0, >= 0</td></tr>
<tr><td><tt>AF</tt></td> <td>Exponent of current</td>
<td>2, > 0</td></tr>
<tr><td><tt>LF</tt></td> <td>Exp. of eff. length</td>
<td>1, > 0</td></tr>
<tr><td><tt>WF</tt></td> <td>Exp. of eff. width</td>
<td>1, > 0</td></tr>
<tr><td><tt>EF</tt></td> <td>Exp. of frequency</td>
<td>1, > 0</td></tr>
</table>
</blockquote>
<p>
The <tt>noise</tt> parameter will multiply the conductance used in
the noise equations. It provides a default which is overridden by
the instance parameter of the same name. This can be used to
model empirical excess noise, or to remove the devices from noise
analysis by setting the parameter to zero.
!!SEEALSO
.model
!! elements.tex 012609
!!KEYWORD
swmodel
!!TITLE
Switch Models
!!HTML
<b>Type Names:</b> <tt>csw</tt>, <tt>sw</tt>
<p>
The <a href="sw">switch</a> model allows an almost ideal switch to
be described in <i>WRspice</i>. The switch is not quite ideal, in
that the resistance can not change from 0 to infinity, but must
always have a finite positive resistance. By proper selection of
the on and off resistances, they can be effectively zero and
infinity in comparison to other circuit elements. There are two
different types of switch devices; current-controlled (keyed by
<tt>w</tt>), and voltage-controlled (keyed by <tt>s</tt>). Both
reference the model described below. The parameters available
are:
<p>
<table border=1 cellpadding=2 bgcolor="#ffffee">
<caption>Switch Model Parameters</caption>
<tr><th>name</th>
<th>parameter</th>
<th>units</th> <th>default</th> <th>switch</th></tr>
<tr><td><tt>vt</tt></td>
<td>threshold voltage</td>
<td>V</td> <td>0.0</td> <td>S</td></tr>
<tr><td><tt>it</tt></td>
<td>threshold current</td>
<td>A</td> <td>0.0</td> <td>W</td></tr>
<tr><td><tt>vh</tt></td>
<td>hysteresis voltage</td>
<td>V</td> <td>0.0</td> <td>S</td></tr>
<tr><td><tt>ih</tt></td>
<td>hysteresis current</td>
<td>A</td> <td>0.0</td> <td>W</td></tr>
<tr><td><tt>ron</tt></td>
<td>on resistance</td>
<td>O</td> <td>1.0</td> <td>both</td></tr>
<tr><td><tt>roff</tt></td>
<td>off resistance</td>
<td>O</td> <td>1/<a href="gmin"><tt>gmin</tt></a></td>
<td>both</td></tr>
</table>
The <tt>gmin</tt> parameter, can be set on the <a
href=".options"><tt>.options</tt></a> line. Its default value
results is an off resistance of 1.0e+12 ohms.
<p>
The use of an ideal element that is highly nonlinear such as a
switch can cause large discontinuities to occur in the circuit
node voltages. A rapid change such as that associated with a
switch changing state can cause numerical roundoff or tolerance
problems leading to erroneous results or timestep difficulties.
The user of switches can improve the situation by taking the
following steps.
<p>
First of all it is wise to set ideal switch impedances only high
and low enough to be negligible with respect to other circuit
elements. Using switch impedances that are close to "ideal" in
all cases will aggravate the problem of discontinuities mentioned
above. Of course, when modeling real devices such as MOSFETS, the
on resistance should be adjusted to a realistic level depending on
the size of the device being modeled.
<p>
If a wide range of on to off resistance must be used in the
switches (<tt>roff/ron</tt> > 1e+12), then the tolerance on errors
allowed during transient analysis should be decreased by using the
<tt>.options</tt> line and specifying <tt>trtol</tt> to be less
than the default value of 7.0 (options can also be set from the
prompt line from within <i>WRspice</i>). When switches are placed
around capacitors, then the option <tt>chgtol</tt> should also be
reduced. Suggested values for these two options are 1.0 and 1e-16
respectively. These changes inform <i>WRspice</i> to be more
careful around the switch points so that no errors are made due to
the rapid change in the circuit.
!!SEEALSO
.model
!! elements.tex 040410
!!KEYWORD
tramodel ltramodel
!!TITLE
Transmission Line Model
!!HTML
<b>Type Names:</b> <tt>ltra</tt>, <tt>tra</tt>
<p>
The <a href="tra">general transmission line</a> model may be used
in conjunction with transmission line devices, though the use is
optional. The parameters that appear in the model are the same
parameters that can be given on the device line (with the
exception of the initial conditions).
<p>
Transmission line models can have either of two type names:
<tt>tra</tt> or <tt>ltra</tt>. The <tt>ltra</tt> name is required
to support the SPICE3 LTRA lossy transmission line model. If this
name is used, the <tt>level</tt> will default to 2. This will be
overridden if the level is set explicitly. If the <tt>tra</tt>
keyword is used, then the level will default to 1. Otherwise, the
two words are interchangeable.
<p>
The parameters provided in the model will serve as defaults to the
referencing device, but can be overridden if explicitly set on the
device line.
!!SEEALSO
.model
multidec
trytocompact
!! elements.tex 012609
!!KEYWORD
urcmodel
!!TITLE
Uniform RC Line Model
!!HTML
<b>Type Name:</b> <tt>urc</tt>
<p>
The <a href="urc">urc</a> model is derived from a model proposed
by L. Gertzberrg in 1974. The model is accomplished by a
subcircuit type expansion of the URC line into a network of lumped
RC segments with internally generated nodes. The RC segments are
in a geometric progression, increasing toward the middle of the
URC line, with <tt>k</tt> as a proportionality constant. The
number of lumped segments used, if not specified on the urc line,
is determined by the following formula:
<blockquote>
N = log(2pi·<i>Fmax</i>·<i>RC</i>·
((<tt>k</tt>-1)/<tt>k</tt>)<sup>2</sup>) / log(<tt>k</tt>)
</blockquote>
where <i>Fmax</i> is the maximum frequency, and <i>R</i> and
<i>C</i> are the total values for the given length.
<p>
The urc line will be made up strictly of resistor and capacitor
segments unless the <tt>isperl</tt> parameter is given a non-zero
value, in which case the capacitors are replaced with reverse
biased diodes with a zero-bias junction capacitance equivalent to
the capacitance replaced, and with a saturation current taking the
value given <tt>isperl</tt> in amps per meter of transmission
line, and with an optional series resistance specified by
<tt>rsperl</tt> in ohms per meter.
<p>
<table border=1 cellpadding=2 bgcolor="#ffffee">
<caption>URC Model Parameters</caption>
<tr><th>name</th>
<th>parameter</th>
<th>units</th> <th>default</th> <th>example</th></tr>
<tr><td><tt>k</tt></td>
<td>propagation constant</td>
<td>-</td> <td>1.5</td> <td>1.2</td></tr>
<tr><td><tt>fmax</tt></td>
<td>maximum frequency</td>
<td>Hz</td> <td>1.0G</td> <td>6.5meg</td></tr>
<tr><td><tt>rperl</tt></td>
<td>resistance per length</td>
<td>O/M</td> <td>1000</td> <td>10</td></tr>
<tr><td><tt>cperl</tt></td>
<td>capacitance per length</td>
<td>F/M</td> <td>1.0e-12</td><td>2pF</td></tr>
<tr><td><tt>isperl</tt></td>
<td>saturation current per length</td>
<td>A/M</td> <td>0</td> <td>-</td></tr>
<tr><td><tt>rsperl</tt></td>
<td>diode resistance per length</td>
<td>O/M</td> <td>0</td> <td>-</td></tr>
</table>
!!SEEALSO
.model
!! elements.tex 100311
!!KEYWORD
diomodel
!!TITLE
Junction Diode Model
!!HTML
<b>Type Name:</b> <tt>d</tt>
<p>
The dc characteristics of the <a href="dio">diode</a> are
determined by the parameters <tt>is</tt> and <tt>n</tt>. An ohmic
resistance, <tt>rs</tt>, is included. Charge storage effects are
modeled by a transit time, <tt>tt</tt>, and a nonlinear depletion
layer capacitance which is determined by the parameters
<tt>cjo</tt>, <tt>vj</tt>, and <tt>m</tt>. The temperature
dependence of the saturation current is defined by the parameters
<tt>eg</tt>, the energy and <tt>xti</tt>, the saturation current
temperature exponent. The nominal temperature at which these
parameters were measured is <tt>tnom</tt>, which defaults to the
value specified on the <a href=".options"><tt>.options</tt></a>
control line. Reverse breakdown is modeled by an exponential
increase in the reverse diode current and is determined by the
parameters <tt>bv</tt> and <tt>ibv</tt> (both of which are
positive numbers).
<p>
The diode model is an enhanced version of the SPICE3 diode model,
as used in NGspice, but with additional support for <a
href="hspicesim">HSPICE</a> model parameters.
<p>
The parameters marked with an asterisk in the <b>area</b> column
scale with the <tt>area</tt> and/or the <tt>m</tt> (multiplicity)
parameters given in the device line. The parameters marked with
two asterisks scale with the <tt>pj</tt> (perimeter factor)
parameter given in the device line.
<p>
<table border=1 cellpadding=2 bgcolor="#ffffee">
<caption>Diode Model Parameters</caption>
<tr><th>name</th> <th>area</th>
<th>parameter</th>
<th>units</th> <th>default</th> <th>example</th></tr>
<tr><td><tt>is, js</tt></td> <td>*</td>
<td>saturation current</td>
<td>A</td> <td>1.0e-14</td> <td>1.0e-14</td></tr>
<tr><td><tt>jsw</tt></td> <td>**</td>
<td>sidewall saturation current</td>
<td>A</td> <td>0</td> <td> </td></tr>
<tr><td><tt>rs</tt></td> <td>*</td>
<td>ohmic resistance</td>
<td>O</td> <td>0</td> <td>10</td></tr>
<tr><td><tt>trs, trs1</tt></td> <td> </td>
<td>ohmic resistance 1st order temp. coeff.</td>
<td>-</td> <td>0</td> <td> </td></tr>
<tr><td><tt>trs2</tt></td> <td> </td>
<td>ohmic resistance 2nd order temp. coeff.</td>
<td>-</td> <td>0</td> <td> </td></tr>
<tr><td><tt>n</tt></td> <td> </td>
<td>emission coefficient</td>
<td>-</td> <td>1</td> <td>1.0</td></tr>
<tr><td><tt>tt</tt></td> <td> </td>
<td>transit-time</td>
<td>S</td> <td>0</td> <td>0.1nS</td></tr>
<tr><td><tt>tt1</tt></td> <td> </td>
<td>transit-time 1st order temp. coeff.</td>
<td>-</td> <td>0</td> <td> </td></tr>
<tr><td><tt>tt2</tt></td> <td> </td>
<td>transit-time 2nd order temp. coeff.</td>
<td>-</td> <td>0</td> <td> </td></tr>
<tr><td><tt>cjo, cj0, cj</tt></td> <td>*</td>
<td>zero-bias junction capacitance</td>
<td>F</td> <td>0</td> <td>2pF</td></tr>
<tr><td><tt>vj, pb</tt></td> <td> </td>
<td>junction potential</td>
<td>V</td> <td>1</td> <td>0.6</td></tr>
<tr><td><tt>m, mj</tt></td> <td> </td>
<td>grading coefficient</td>
<td>-</td> <td>0.5</td> <td>0.5</td></tr>
<tr><td><tt>tm1</tt></td> <td> </td>
<td>grading coefficient 1st temp. coeff.</td>
<td>-</td> <td>0</td> <td> </td></tr>
<tr><td><tt>tm2</tt></td> <td> </td>
<td>grading coefficient 2nd temp. coeff.</td>
<td>-</td> <td>0</td> <td> </td></tr>
<tr><td><tt>cjp, cjsw</tt></td> <td>**</td>
<td>sidewall junction capacitance</td>
<td>F</td> <td>0</td> <td> </td></tr>
<tr><td><tt>php</tt></td> <td> </td>
<td>sidewall junction potential</td>
<td>V</td> <td>0</td> <td> </td></tr>
<tr><td><tt>mjsw</tt></td> <td> </td>
<td>sidewall grading coefficient</td>
<td>-</td> <td>0.33</td> <td> </td></tr>
<tr><td><tt>ikf, ik</tt></td> <td>*</td>
<td>forward knee current</td>
<td>A</td> <td>1e-3</td> <td> </td></tr>
<tr><td><tt>ikr</tt></td> <td>*</td>
<td>reverse knee current</td>
<td>A</td> <td>1e-3</td> <td> </td></tr>
<tr><td><tt>eg</tt></td> <td> </td>
<td>activation energy</td>
<td>eV</td> <td>1.11</td> <td> 1.11 Si<br>0.69 Sbd<br>0.67 Ge</td></tr>
<tr><td><tt>xti</tt></td> <td> </td>
<td>saturation-current temp. exponent</td>
<td>-</td> <td>3.0</td> <td>3.0 junc<br>2.0 Sbd</td></tr>
<tr><td><tt>kf</tt></td> <td> </td>
<td>flicker noise coefficient</td>
<td>-</td> <td>0</td> <td> </td></tr>
<tr><td><tt>af</tt></td> <td> </td>
<td>flicker noise exponent</td>
<td>-</td> <td>1</td> <td> </td></tr>
<tr><td><tt>fc</tt></td> <td> </td>
<td>forward-bias junction fit parameter</td>
<td>-</td> <td>0.5</td> <td> </td></tr>
<tr><td><tt>fcs</tt></td> <td> </td>
<td>forward-bias sidewall junction fit parameter</td>
<td>-</td> <td>0.5</td> <td> </td></tr>
<tr><td><tt>bv</tt></td> <td> </td>
<td>reverse breakdown voltage</td>
<td>V</td> <td>infinite</td> <td>40.0</td></tr>
<tr><td><tt>ibv</tt></td> <td>*</td>
<td>current at reverse breakdown voltage</td>
<td>A</td> <td>1.0E-3</td> <td> </td></tr>
<tr><td><tt>tnom, tref</tt></td> <td> </td>
<td>parameter measurement temperature</td>
<td>C</td> <td>25</td> <td>50</td></tr>
<tr><th colspan=6>HSPICE Compatibility</th></tr>
<tr><td><tt>level</tt></td> <td> </td>
<td>device type selector</td>
<td>-</td> <td> </td> <td> </td></tr>
<tr><td><tt>tlev</tt></td> <td> </td>
<td>equation set selector</td>
<td>-</td> <td> </td> <td> </td></tr>
<tr><td><tt>tlevc</tt></td> <td> </td>
<td>equation set selector</td>
<td>-</td> <td> </td> <td> </td></tr>
<tr><td><tt>area</tt></td> <td> </td>
<td>area default</td>
<td>-</td> <td> </td> <td> </td></tr>
<tr><td><tt>pj</tt></td> <td> </td>
<td>sidewall perimeter factor default</td>
<td>-</td> <td> </td> <td> </td></tr>
<tr><td><tt>cta</tt></td> <td> </td>
<td>junction capacitance temp. coeff.</td>
<td>-</td> <td> </td> <td> </td></tr>
<tr><td><tt>ctp</tt></td> <td> </td>
<td>sidewall capacitance temp. coeff.</td>
<td>-</td> <td> </td> <td> </td></tr>
<tr><td><tt>tcv</tt></td> <td> </td>
<td>breakdown voltage temp. coeff.</td>
<td>-</td> <td> </td> <td> </td></tr>
<tr><td><tt>pb</tt></td> <td> </td>
<td>junction potential temp. coeff.</td>
<td>-</td> <td> </td> <td> </td></tr>
<tr><td><tt>php</tt></td> <td> </td>
<td>sidewall potential temp. coeff.</td>
<td>-</td> <td> </td> <td> </td></tr>
</table>
<p>
The <a href="hspicesim">HSPICE</a> compatibility parameters
provide some minimal compatibility with the HSPICE diode model.
The <tt>level</tt> parameter, if present, can take values of 1 and
3, corresponding to the HSPICE junction and geometric junction
models. There is presently no support for the <tt>level=2</tt>
Fowler-Nordheim model. The <tt>tlev</tt> and <tt>tlevc</tt>
parameters switch equation sets. Both take values of 0 and 1, and
if set to any other value will assume a value of 1, i.e., higher
values are not supported. The remaining parameters are as defined
in the HSPICE documentation.
!!SEEALSO
.model
!! elements.tex 091511
!!KEYWORD
bjtmodel
!!TITLE
BJT Models
!!HTML
<b>Type Names:</b> <tt>npn</tt>, <tt>pnp</tt>
<p>
The <a href="bjt">bipolar junction transistor</a> model in
<i>WRspice</i> is an adaptation of the integral charge control
model of Gummel and Poon. This modified Gummel-Poon model extends
the original model to include several effects at high bias levels.
The model will automatically simplify to the simpler Ebers-Moll
model when certain parameters are not specified. The parameter
names used in the modified Gummel-Poon model have been chosen to
be more easily understood by the program user, and to reflect
better both physical and circuit design thinking.
<p>
The dc model is defined by the parameters <tt>is</tt>,
<tt>bf</tt>, <tt>nf</tt>, <tt>ise</tt>, <tt>ikf</tt>, and
<tt>ne</tt> which determine the forward current gain
characteristics, <tt>is</tt>, <tt>br</tt>, <tt>nr</tt>,
<tt>isc</tt>, <tt>ikr</tt>, and <tt>nc</tt> which determine the
reverse current gain characteristics, and <tt>vaf</tt> and
<tt>var</tt> which determine the output conductance for forward
and reverse regions. Three ohmic resistances <tt>rb</tt>,
<tt>rc</tt>, and <tt>re</tt> are included, where <tt>rb</tt> can
be high current dependent. Base charge storage is modeled by
forward and reverse transit times, <tt>tf</tt> and <tt>tr</tt>,
the forward transit time <tt>tf</tt> being bias dependent if
desired, and nonlinear depletion layer capacitances which are
determined by <tt>cje</tt>, <tt>vje</tt>, and <tt>mje</tt> for the
B-E junction , <tt>cjc</tt>, <tt>vjc</tt>, and <tt>mjc</tt> for
the B-C junction and <tt>cjs</tt>, <tt>vjb</tt>, and <tt>mjs</tt>
for the C-S (Collector-Substrate) junction. The temperature
dependence of the saturation current, <tt>is</tt>, is determined
by the energy-gap, <tt>eg</tt>, and the saturation current
temperature exponent, <tt>xti</tt>. Additionally base current
temperature dependence is modeled by the beta temperature exponent
<tt>xtb</tt> in the new model. The values specified are assumed
to have been measured at the temperature <tt>tnom</tt>, which can