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Updated diode documentation.

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pnenzi 23 years ago
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      doc/ngspice.texi

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@ -674,6 +674,11 @@ the GNU Autoconf documentation for the former.
The options specific to NGSPICE are:
@itemize @bullet
@item @command{--enable-numaparam}: Preliminary support for parameters expansion
in netlists. Numparam is a library that attach itself to a single point
in NGSPICE code and comes with its own documentation. Before using this
library you should look at library's documentation in @file{src/frontend/numaparam}
directory.
@item @command{--enable-ftedebug}: This switch enables the code for debugging
the NGSPICE frontend. Developers who wish to mess with the frontend
should enable it (and set to @code{TRUE} the "debug" option). The
@ -733,10 +738,7 @@ The options specific to NGSPICE are:
this to have it compiled into NGSPICE.
@item @command{--with-readline}: This option enables GNU Readline on NGSPICE.
Since NGSPICE license is incompatible with GPL (which covers Readline
library), the code is not included into NGSPICE by default. The Readline
code is delivered as a separate patch. Before enabling this option the
patch must be applied. @emph{Applying the patch will break the GPL,
consider this!}
library), the code is not included compiled into NGSPICE by default.
@end itemize
@sc{Caveat Emptor}:
@ -1101,19 +1103,40 @@ stationary gaussian process.
@node Analysis at Different Temperatures, Convergence, Types of Analysis, Supported Analyses
@section Analysis at Different Temperatures
All input data for NGSPICE is assumed to have been measured at a nominal
temperature of 27°C, which can be changed by use of the @code{TNOM}
parameter on the @code{.OPTION} control line. This value can further be
overridden for any device which models temperature effects by
specifying the @code{TNOM} parameter on the model itself. The circuit
simulation is performed at a temperature of 27°C, unless
overridden by a @code{TEMP} parameter on the @code{.OPTION} control line.
Temperature, in NGSPICE, is a property associated to the entire circuit,
rather an analysis option. Circuit temperature has a default (nominal)
value of 27°C (300.15 K) that can be changed using the @option{TNOM}
option in an @code{.OPTION} control line. All analyses are, thus,
performed at circuit temperature, and if you want to simulate circuit
behaviour at different tempereratures you should prepare a netlist
for each temperature.
All input data for NGSPICE is assumed to have been measured at the
circuit nominal temperature. This value can further be overridden for
any device which models temperature effects by specifying the @option{TNOM}
parameter on the @code{.model} itself.
Individual instances may further override the circuit temperature
through the specification of a @code{TEMP} parameter on the instance.
through the specification of @option{TEMP} and @option{DTEMP} parameters
on the instance. The two options are not independent even if you can
specify both on the instance line, the @option{TEMP} option overrides
@option{DTEMP}. The algorithm to compute instance temperature is described
below:
@example
IF TEMP is specified THEN
instance_temperature = TEMP
ELSE IF
instance_temperature = circuit_temperature + DTEMP
END IF
Temperature dependent support is provided for resistors, diodes,
JFETs, BJTs, and level 1, 2, and 3 MOSFETs. BSIM (levels 4 and 5)
MOSFETs have an alternate temperature dependency scheme which adjusts
@end example
Temperature dependent support is provided for all devices except voltage
and current sources (either independent and controlled) and BSIM models.
BSIM MOSFETs have an alternate temperature dependency scheme which adjusts
all of the model parameters before input to NGSPICE. For details of the
BSIM temperature adjustment, see [6] and [7].
@ -1141,10 +1164,10 @@ $$
@end example
@end ifnottex
where `k' is Boltzmann's constant, `q' is the electronic charge, `E'
is the energy gap which is a model parameter, `G' and `XTI' is the
saturation current temperature exponent (also a model parameter, and
usually equal to 3).
where `@math{k}' is Boltzmann's constant, `@math{q}' is the electronic
charge, `@math{E}' is the energy gap which is a model parameter, `@math{G}'
and `@math{XTI}' is the saturation current temperature exponent (also a
model parameter, and usually equal to 3).
@ -1169,10 +1192,11 @@ $$
@end ifnottex
where `T_0' and `T_1' are in degrees Kelvin, and `XTB' is a user-supplied
model parameter. Temperature effects on beta are carried out by appropriate
adjustment to the values of `B_F' , `I_SE' , `B_R' , and `I_SC' (spice model
parameters @code{BF}, @code{ISE}, @code{BR}, and @code{ISC}, respectively).
where `@math{T_0}' and `@math{T_1}' are in degrees Kelvin, and `@math{XTB}'
is a user-supplied model parameter. Temperature effects on beta are carried
out by appropriate adjustment to the values of `@math{B_F}', `@math{I_SE}',
`@math{B_R}', and `@math{I_SC}' (spice model parameters @option{BF},
@option{ISE}, @option{BR}, and @option{ISC}, respectively).
@ -1201,16 +1225,16 @@ $$
@end ifnottex
where @code{N} is the emission coefficient, which is a model parameter, and the
where `@math{N}' is the emission coefficient, which is a model parameter, and the
other symbols have the same meaning as above. Note that for Schottky
barrier diodes, the value of the saturation current temperature
exponent, @code{XTI}, is usually 2.
exponent, `@math{XTI}', is usually 2.
Temperature appears explicitly in the value of junction potential, `U'
(in NGSPICE @code{PHI}), for all the device models. The temperature
dependence is determined by:
Temperature appears explicitly in the value of junction potential,
`@option{U}' (in NGSPICE @option{PHI}), for all the device models.
The temperature dependence is determined by:
@tex
$$
@ -1228,16 +1252,16 @@ $$
@end example
@end ifnottex
where `k' is Boltzmann's constant, `q' is the electronic charge, `N_a'
is the acceptor impurity density, `N_d' is the donor impurity density,
`N_i' is the intrinsic carrier con centration, and `E_g' is the energy
gap.
where `@math{k}' is Boltzmann's constant, `@math{q}' is the electronic
charge, `@math{N_a}' is the acceptor impurity density, `@math{N_d}' is
the donor impurity density, `@math{N_i}' is the intrinsic carrier
concentration, and `@math{E_g}' is the energy gap.
Temperature appears explicitly in the value of surface mobility, `M_0'
(or UO), for the MOSFET model. The temperature dependence is
determined by:
Temperature appears explicitly in the value of surface mobility,
`@math{M_0}' (or @math{U_0}), for the MOSFET model. The temperature
dependence is determined by:
@tex
$$
@ -1257,7 +1281,8 @@ $$
@end example
@end ifnottex
The effects of temperature on resistors is modeled by the formula:
The effects of temperature on resistors, capacitor and inductors is modeled
by the formula:
@tex
$$
@ -1272,8 +1297,8 @@ $$
@end example
@end ifnottex
where `T' is the circuit temperature, `T_0' is the nominal temperature,
and `TC_1' and `TC_2' are the first- and second order temperature
where `@math{T}' is the circuit temperature, `@math{T_0}' is the nominal temperature,
and `@math{TC_1}' and `@math{TC_2}' are the first and second order temperature
coefficients.
@ -1327,7 +1352,7 @@ converge to the desired state.
@node General Structure and Conventions, Basics, Circuit Description, Circuit Description
@section General Structure and Conventions
The circuit to be analyzed is described to NGSPICE by a set of element
The circuit to be analyzed is described to ngspice by a set of element
lines, which define the circuit topology and element values, and a set
of control lines, which define the model parameters and the run
controls. The first line in the input file must be the title, and the
@ -1535,6 +1560,10 @@ Semiconductor resistor model
Semiconductor capacitor model
@item L
Inductor model
@item SW
Voltage controlled switch
@ -1741,13 +1770,67 @@ in the direction of voltage drop).
@menu
* General options and information::
* Elementary Devices::
* Voltage and Current Sources::
* Transmission Lines::
* Transistors and Diodes::
@end menu
@node Elementary Devices, Voltage and Current Sources, Circuit Elements and Models, Circuit Elements and Models
@node General options and information, Elementary Devices, Circuit Elements and Models, Circuit Elements and Models
@section General options and information
@menu
* Simulating more devices in parallel::
* Technology scaling::
* Model binning::
@end menu
@node Simulating more devices in parallel, Technology scaling, General options and information, General options and information
@subsection Simulating more devices in parallel
If you need to simulate more devices of the same kind in parallel, you
can use the @option{m} (often called parallel multiplier) option which
is available for all instances except transmission lines and sources
(both independent and controlled).
The parallel multiplier is implemented by multiplying by the value of
@option{m} the element's matrix stamp, thus it cannot be used to accurately
simulate larger devices in integrated circuits.
The netlist below show how to correclty use the parallel multiplier:
@example
Multiple devices
d1 2 0 mydiode m=10
d01 1 0 mydiode
d02 1 0 mydiode
d03 1 0 mydiode
d04 1 0 mydiode
d05 1 0 mydiode
d06 1 0 mydiode
d07 1 0 mydiode
d08 1 0 mydiode
d09 1 0 mydiode
d10 1 0 mydiode
...
@end example
The @code{d1} instance connected between nodes 2 and 0 is equivalent
to the parallel @code{d01-d10} connected between 1 and 0.
@node Technology scaling, Model binning, Simulating more devices in parallel, General options and information
@subsection Technology scaling
Still to be implemented and written.
@node Model Binning, Elementary Devices, Technology scaling, General options and information
@subsection Model binning
Still to be implemented and written.
@node Elementary Devices, General options and information, Circuit Elements and Models, Circuit Elements and Models
@section Elementary Devices
@ -1789,35 +1872,24 @@ discrete and semiconductor resistors. Semiconductor resistors in ngspice
means: resistors described by geometrical parameters. So, do not expect
detailed modeling of semiconductor effects.
@option{n+} and @option{n-} are the two element nodes, @option{value} is the
resistance (in ohms) and may be positive or negative but not zero. If you
need to simulate very small resistors (0.001 Ohm or less) , you should use
CCVS (transresistance), it is less efficient but improves numerical
accuracy (a small resistance is a large conductance).
@option{n+} and @option{n-} are the two element nodes, @option{value} is
the resistance (in ohms) and may be positive or negative but not zero.
@sc{Hint}: If you need to simulate very small resistors (0.001 Ohm or
less), you should use CCVS (transresistance), it is less efficient but
improves overall numerical accuracy. Think about that a small resistance
is a large conductance.
Ngspice can assign a resistor instance a different value for AC analysis,
specified using the @option{ac} keyword. This value must not be zero as
described above. The AC resistance is used in AC analysis only (not Pole-Zero
nor noise). If you do not specify the @option{ac} parameter, it is defaulted
to @option{value}.
The @option{m} parameter is the "multiplication factor", and can be used to
simulate "m" instances of the same kind in parallel. This parameter affects
all analyses.
nor noise). If you do not specify the @option{ac} parameter, it is
defaulted to @option{value}.
The @option{scale} keyword let the designer choose a different scale for
elements. This option is not yet very useful, it will fully implemented in the
future to perform technology scaling. At present is here as a work in progress.
If you want to simulate temperature dependence of a resistor, you need
to specify its temperature coefficients, using a @command{.model} line,
like in the example below:
The operating temperature of instances can be changed using the @option{dtemp}
keyword. Ngspice simulates the circuit with all components at the same single
temperature (the circuit temperature). To adjust the temperature of a resistor
instance you can define its temperature difference from the rest of the
circuit using @option{dtemp}.
If you want to simulate temperature dependence of a resistor, you need to
specify its temperature coefficients, using a @command{.model} line, like in the
example below:
@example
RE1 1 2 700 std dtemp=5
@ -1855,8 +1927,8 @@ $$
@end example
@end ifnottex
If you are interested in temperature effects or noise equations, read the
following section on semiconductor resistors.
If you are interested in temperature effects or noise equations, read
the following section on semiconductor resistors.
@node Semiconductor Resistors, Semiconductor Resistor Model (R), Resistors, Elementary Devices
@subsection Semiconductor Resistors
@ -1877,18 +1949,18 @@ following section on semiconductor resistors.
@end example
This is the more general form of the resistor presented before (@pxref{Resistors})
and allows the modeling of temperature effects and for the calculation of the
actual resistance value from strictly geometric information and the
specifications of the process. If @option{value} is specified, it overrides
the geometric information and defines the resistance. If @option{mname} is
specified, then the resistance may be calculated from the process information
in the model @option{mname} and the given @option{length} and @option{width}.
If @option{value} is not specified, then @option{mname} and @option{length}
must be specified. If @option{width} is not specified, then it is taken
from the default width given in the model.
The (optional) @option{temp} value is the temperature at which this device is
to operate, and overrides the temperature specification on the
and allows the modeling of temperature effects and for the calculation
of the actual resistance value from strictly geometric information and
the specifications of the process. If @option{value} is specified, it
overrides the geometric information and defines the resistance. If
@option{mname} is specified, then the resistance may be calculated from
the process information in the model @option{mname} and the given @option{length}
and @option{width}. If @option{value} is not specified, then @option{mname}
and @option{length} must be specified. If @option{width} is not specified,
then it is taken from the default width given in the model.
The (optional) @option{temp} value is the temperature at which this device
is to operate, and overrides the temperature specification on the
@command{.option} control line and the value specified in @option{dtemp}.
@ -1926,7 +1998,7 @@ corrected for temperature. The parameters available are:
The sheet resistance is used with the narrowing parameter and @option{l}
and @option{w} from the resistor device to determine the nominal resistance
by the formula
by the formula:
@tex
$$
@ -1966,7 +2038,7 @@ where $R({\rm TNOM}) = R_{nom} \vert R_{acnom}$.
@end example
@end ifnottex
In the above formula, "T" represents the instance temperature, which can be
In the above formula, `@math{T}' represents the instance temperature, which can be
explicitly using the @option{temp} keyword or os calculated using the
circuit temperature and @option{dtemp}, if present.
@ -2066,20 +2138,6 @@ in a @command{.model} line, as in the example below:
Both capacitors have a capacitance of 3nF.
The @option{m} parameter is the "multiplication factor", and can be used to
simulate "m" instances of the same kind in parallel. This parameter affects
all analyses.
The @option{scale} keyword let the designer choose a different scale for
elements. This option is not yet very useful, it will fully implemented in the
future to perform technology scaling. At present is here as a work in progress.
The operating temperature of instances can be changed using the @option{dtemp}
keyword. Ngspice simulates the circuit with all components at the same single
temperature (the circuit temperature). To adjust the temperature of a capacitor
instance you can define its temperature difference from the rest of the
circuit using @option{dtemp}.
If you want to simulate temperature dependence of a capacitor, you need to
specify its temperature coefficients, using a @command{.model} line, like in the
example below:
@ -2305,11 +2363,10 @@ where $C({\rm TNOM}) = C_{nom}$.
@end example
@end ifnottex
In the above formula, "T" represents the instance temperature, which can be
In the above formula, `@math{T}' represents the instance temperature, which can be
explicitly using the @option{temp} keyword or os calculated using the
circuit temperature and @option{dtemp}, if present.
If both @option{temp} and @option{dtemp} are specified, the latter is ignored.
@node Inductors, Inductor model, Semiconductor Capacitor Model (C), Elementary Devices
@ -2330,12 +2387,12 @@ If both @option{temp} and @option{dtemp} are specified, the latter is ignored.
LSHUNT 23 51 10U IC=15.7MA
@end example
The inductor device implemented into ngspice has many enhancements over the
orginal one. @option{n+} and @option{n-} are the positive and negative element
nodes, respectively. @option{value} is the inductance in Henries.
The inductor device implemented into ngspice has many enhancements over
the orginal one. @option{n+} and @option{n-} are the positive and negative
element nodes, respectively. @option{value} is the inductance in Henries.
Inductance can be specified in the instance line as in the examples above or
in a @command{.model} line, as in the example below:
Inductance can be specified in the instance line as in the examples above
or in a @command{.model} line, as in the example below:
@example
L1 15 5 indmod1
@ -2346,26 +2403,12 @@ in a @command{.model} line, as in the example below:
Both inductors have an inductance of 3nH.
The @option{m} parameter is the "multiplication factor", and can be used to
simulate "m" instances of the same kind in parallel. This parameter affects
all analyses.
The @option{scale} keyword let the designer choose a different scale for
elements. This option is not yet very useful, it will fully implemented in the
future to perform technology scaling. At present is here as a work in progress.
The @option{nt} is used in conjunction with a @command{.model} line, and
is used to specify the number of turns of the inductor.
The @option{nt} is used in conjunction with a @command{.model} line, and is used
to specify the number of turns of the inductor.
The operating temperature of instances can be set using the @option{temp}
option. Ngspice simulates the circuit with all components at the same single
temperature (the circuit temperature). To adjust the temperature of an
inductor instance you can define its temperature difference from the rest of
the circuit using @option{dtemp}.
If you want to simulate temperature dependence of an inductor, you need to
specify its temperature coefficients, using a @command{.model} line, like in
the example below:
If you want to simulate temperature dependence of an inductor, you need
to specify its temperature coefficients, using a @command{.model} line,
like in the example below:
@example
Lload 1 2 1u ind1 dtemp=5
@ -2374,9 +2417,10 @@ the example below:
@end example
The (optional) initial condition is the initial (timezero) value of
inductor current (in Amps) that flows from @option{n+}, through the inductor,
to @option{n-}. Note that the initial conditions (if any) apply only if the
@option{UIC} option is specified on the @command{.tran} analysis line.
inductor current (in Amps) that flows from @option{n+}, through the
inductor, to @option{n-}. Note that the initial conditions (if any)
apply only if the @option{UIC} option is specified on the @command{.tran}
analysis line.
Ngspice calculates the nominal inductance as described below:
@ -2395,10 +2439,10 @@ $$
@node Inductor model, Coupled (Mutual) Inductors, Inductors, Elementary Devices
@subsection Inductor model
The inductor model contains physical and geometrical information that may be used to
compute the inductance in some special cases (solenoid, toroid) In the present
form is not very useful, but may be extended in the future to accomodate
silicon integrated inductors, an emerging technology.
The inductor model contains physical and geometrical information that
may be used to compute the inductance of some common topologies like
solenoids and toroids, wound in air or other material with constant
magnetic permeability.
@multitable @columnfractions .15 .4 .2 .1 .1
@item name @tab parameter @tab units @tab default @tab example
@ -2448,10 +2492,10 @@ $$
@end example
@end ifnottex
If neither @option{value} nor @option{IND} are specified, then geometrical and
physical parameters are take into account. In the following formulas @option{NT}
refers to both instance and model parameter (instance parameter overrides model
parameter):
If neither @option{value} nor @option{IND} are specified, then geometrical
and physical parameters are take into account. In the following formulas
@option{NT} refers to both instance and model parameter (instance parameter
overrides model parameter):
If @option{LENGTH} is not zero:
@ -2515,12 +2559,9 @@ where $L({\rm TNOM}) = L_{nom}$.
@end example
@end ifnottex
In the above formula, "T" represents the instance temperature, which can be
explicitly using the @option{temp} keyword or os calculated using the
circuit temperature and @option{dtemp}, if present.
If both @option{temp} and @option{dtemp} are specified, the latter is ignored.
In the above formula, `@math{T}' represents the instance temperature,
which can be explicitly using the @option{temp} keyword or calculated
using the circuit temperature and @option{dtemp}, if present.
@node Coupled (Mutual) Inductors, Switches, Inductor model, Elementary Devices
@ -3481,7 +3522,8 @@ conditions.
@menu
* Junction Diodes::
* Diode Model (D)::
* Diode Model (D)::
* Diode Equations::
* Bipolar Junction Transistors (BJTs)::
* BJT Models (NPN/PNP)::
* Junction Field-Effect Transistors (JFETs)::
@ -3500,7 +3542,8 @@ conditions.
General form:
@example
DXXXXXXX N+ N- MNAME <AREA> <OFF> <IC=VD> <TEMP=T>
DXXXXXXX n+ n- mname <area=val> <pj=val> <off> <ic=vd> <temp=val>
+ <dtemp=val>
@end example
@ -3512,59 +3555,317 @@ conditions.
@end example
The pn junction (diode) implemented in NGSPICE expands the original
spice's implementation. Perimetral effects and high injection level
have been introduced into the original model and temperature dependence
of some parameters has beed added.
N+ and N- are the positive and negative nodes, respectively. MNAME is
the model name, AREA is the area factor, and OFF indicates an (optional)
starting condition on the device for dc analysis. If the area factor is
omitted, a value of 1.0 is assumed. The (optional) initial condition
specification using IC=VD is intended for use with the UIC option on the
.TRAN control line, when a transient analysis is desired starting from
other than the quiescent operating point. The (optional) TEMP value is
the temperature at which this device is to operate, and overrides the
temperature specification on the .OPTION control line.
@option{n+} and @option{n-} are the positive and negative nodes, respectively.
@option{mname} is the model name, @option{area} is the area factor, @option{pj}
is the perimeter factor, and @option{off} indicates an (optional)starting
condition on the device for dc analysis. If the area factor is omitted,
a value of 1.0 is assumed. The (optional) initial condition specification
using @option{ic} is intended for use with the @option{uic} option on
the @code{.tran} control line, when a transient analysis is desired starting
from other than the quiescent operating point. You should supply the inital
voltage across the diode there. The (optional) @option{temp} value is
the temperature at which this device is to operate, and overrides the
temperature specification on the @code{.option} control line. As always,
instance temperature can be specified as an offset to the circuit
temperature with the @option{dtemp} option.
@node Diode Model (D), Bipolar Junction Transistors (BJTs), Junction Diodes, Transistors and Diodes
@node Diode Model (D), Diode Equations, Junction Diodes, Transistors and Diodes
@subsection Diode Model (D)
The dc characteristics of the diode are determined by the parameters IS
and N. An ohmic resistance, RS, is included. Charge storage effects
are modeled by a transit time, TT, and a nonlinear depletion layer
capacitance which is determined by the parameters CJO, VJ, and M. The
temperature dependence of the saturation current is defined by the
parameters EG, the energy and XTI, the saturation current temperature
exponent. The nominal temperature at which these parameters were
measured is TNOM, which defaults to the circuit-wide value specified on
the .OPTIONS control line. Reverse breakdown is modeled by an
exponential increase in the reverse diode current and is determined by
the parameters BV and IBV (both of which are positive numbers).
The dc characteristics of the diode are determined by the parameters
@option{IS} and @option{N}. An ohmic resistance, @option{RS}, is
included. Charge storage effects are modeled by a transit time,
@option{TT}, and a nonlinear depletion layer capacitance which is
determined by the parameters @option{CJO}, @option{VJ}, and @option{M}.
The temperature dependence of the saturation current is defined by the
parameters @option{EG}, the energy and @option{XTI}, the saturation
current temperature exponent. The nominal temperature at which these
parameters were measured is @option{TNOM}, which defaults to the
circuit-wide value specified on the @code{.options} control line.
Reverse breakdown is modeled by an exponential increase in the
reverse diode current and is determined by the parameters @option{BV}
and @option{IBV} (both of which are positive numbers).
@sc{Junction DC parameters}
@multitable @columnfractions .10 .40 .1 .15 .15 .10
@item name @tab parameter @tab units @tab default @tab example @tab scale factor
@item BV @tab reverse breakdown voltage @tab V @tab infinite @tab 40.0
@item IBV @tab current at breakdown voltage @tab A @tab 1.0e-3 @tab 1.0e-4
@item IK (IKF) @tab forward knee current @tab A @tab 1.0e-3 @tab 1.0e-6
@item IK @tab reverse knee current @tab A @tab 1.0e-3 @tab 1.0e-6
@item IS (JS) @tab saturation current @tab A @tab 1.0e-14 @tab 1.0e-16 @tab area
@item JSW @tab Sidewall saturation current @tab A @tab 1.0e-14 @tab 1.0e-15 @tab perim.
@item N @tab emission coefficient @tab - @tab 1 @tab 1.5
@item RS @tab ohmic resistance @tab Ohm @tab 0 @tab 100 @tab 1/area
@end multitable
@multitable @columnfractions .1 .45 .15 .15 .15 .1
@item name @tab parameter @tab units @tab default @tab example @tab area
@item IS @tab saturation current @tab A @tab 1.0e-14 @tab 1.0e-14 @tab *
@item RS @tab ohmic resistance @tab Z @tab 0 @tab 10 @tab *
@item N @tab emission coefficient @tab - @tab 1 @tab 1.0
@item TT @tab transit-time @tab sec @tab 0 @tab 0.1ns
@item CJO @tab zero-bias junction capacitance
@tab F @tab 0 @tab 2pF @tab *
@item VJ @tab junction potential @tab V @tab 1 @tab 0.6
@item M @tab grading coefficient @tab - @tab 0.5 @tab 0.5
@item EG @tab activation energy
@tab eV @tab 1.11 @tab 1.11 Si; 0.69 Sbd; 0.67 Ge
@item XTI @tab saturation-current temp. exp
@tab - @tab 3.0 @tab 3.0 jn; 2.0 Sbd
@item KF @tab flicker noise coefficient @tab - @tab 0
@item AF @tab flicker noise exponent @tab - @tab 1
@item FC @tab coefficient for forward-bias
@tab - @tab 0.5 @tab depletion capacitance formula
@item BV @tab reverse breakdown voltage @tab V @tab infinite @tab 40.0
@item IBV @tab current at breakdown voltage @tab A @tab 1.0e-3
@sc{Junction capacitance paramters}
@multitable @columnfractions .10 .40 .1 .15 .15 .10
@item name @tab parameter @tab units @tab default @tab example @tab scale factor
@item CJO (CJ0) @tab zero-bias junction bottowall capacitance @tab F @tab 0.0 @tab 2pF @tab area
@item CJP (CJSW) @tab zero-bias junction sidewall capacitance @tab F @tab 0.0 @tab .1pF @tab perim.
@item FC @tab coefficient for forward-bias depletion bottomwall capacitance formula
@tab - @tab 0.5 @tab -
@item FCS @tab coefficient for forward-bias depletion sidewall capacitance formula
@tab - @tab 0.5 @tab -
@item M (MJ) @tab Area junction grading coefficient @tab - @tab 0.5 @tab 0.5
@item MJSW @tab Periphery junction grading coefficient @tab - @tab 0.33 @tab 0.5
@item VJ @tab junction potential @tab V @tab 1 @tab 0.6
@item PHP @tab Periphery junction potential @tab V @tab 1 @tab 0.6
@item TT @tab transit-time @tab sec @tab 0 @tab 0.1ns
@end multitable
@sc{Temperature effects}
@multitable @columnfractions .10 .40 .1 .15 .15 .10
@item name @tab parameter @tab units @tab default @tab example @tab scale factor
@item EG @tab activation energy @tab eV @tab 1.11 @tab 1.11 Si
@item @tab @tab @tab @tab 0.69 Sbd
@item @tab @tab @tab @tab 0.67 Ge
@item TM1 @tab 1st order tempco for MJ @tab 1/°C @tab 0.0 @tab -
@item TM2 @tab 2nd order tempco for MJ @tab 1/°C^2 @tab 0.0 @tab -
@item TNOM @tab parameter measurement temperature @tab C @tab 27 @tab 50
@item TRS @tab 1st order tempco for RS @tab 1/°C^2 @tab 0.0 @tab -
@item TTT1 @tab 1st order tempco for TT @tab 1/°C @tab 0.0 @tab -
@item TTT2 @tab 2nd order tempco for TT @tab 1/°C^2 @tab 0.0 @tab -
@item XTI @tab saturation-current temp. exp @tab - @tab 3.0 @tab 3.0 pn
@item @tab @tab @tab @tab 2.0 Sbd
@end multitable
@sc{Noise modeling}
@multitable @columnfractions .10 .40 .1 .15 .15 .10
@item name @tab parameter @tab units @tab default @tab example @tab scale factor
@item KF @tab flicker noise coefficient @tab - @tab 0
@item AF @tab flicker noise exponent @tab - @tab 1
@end multitable
@node Diode Equations, Bipolar Junction Transistors (BJTs), Diode Model (D), Transistors and Diodes
@subsection Diode Equations
The junction diode is the the basic semiconductor device and the simplest
one modeled in NGSPICE, but it's model is quite complex, even if not
all the physical phenomena affecting a pn junction are modeled. The diode
is modeled in three different regions:
@itemize @bullet
@item
Forward bias: the anode is more positive than the cathode, the
diode is "on" and can conduct large currents. To avoid convergence
problems and unrealistic high current, it is better to specify a
series resistance to limit current with @option{RS} model parameter.
@item
Reverse bias: the cathode is more positive than the anode and
the diode is "off". A reverse biase diode conducts a small leakage
current.
@item
Brakdown: the breakdown region is modeled only if the @option{BV}
model parameter is given. When a diode enters breakdown the current
increase expoentially (remember to limit it). @option{BV} is a
positive value.
@end itemize
@sc{Parameters Scaling}
Model parameters are scaled using the unitless parameters @option{AREA}
and @option{PJ} and the multiplier @option{M} as depicted below:
@tex
$$AREA_{eff} = {\rm AREA}\cdot{\rm M} $$
$$PJ_{eff} = {\rm PJ}\cdot{\rm M} $$
$$IS_{eff} = {\rm IS} \cdot AREA_{eff} + {\rm JSW} * PJ_{eff} $$
$$IBV_{eff} = {\rm IBV}\cdot AREA_{eff}$$
$$IK_{eff} = {\rm IK}\cdot AREA_{eff} $$
$$IKR_{eff} = {\rm IKR}\cdot AREA_{eff} $$
$$CJ_{eff} = {\rm CJ0}\cdot AREA_{eff} $$
$$CJP_{eff} = {\rm CJP}\cdot PJ_{eff} $$
@end tex
@ifnottex
@example
AREAeff = AREA * M
PJeff = PJ * M
ISeff = IS * AREAeff + JSW * PJeff
IKeff = IK * AREAeff
IKReff = IKR * AREAeff
CJeff = CJ0 * AREAeff
CJPeff = CJP * PJeff
@end example
@end ifnottex
@sc{Diode DC, Transient and AC model equations}
@tex
$$
I_D= \cases{IS_{eff} ( e^{q V_D \over N k T} - 1) + V_D * GMIN, &if $V_D \geq -3{NkT \over q}$\cr
-IS_{eff} [1 + ({3NkT \over q V_D e })^3] + V_D * GMIN , &if $-BV_{eff}<V_D<-3{NkT \over q}$\cr
-IS_{eff} ( e^{-q (BV_{eff} + V_D) \over N k T}) + V_D * GMIN, &if $V_D \leq -BV_{eff}$ \cr}
$$
@end tex
@ifnottex
@example
To be written!
@end example
@end ifnottex
The breakdown region must be described with more depth since the breakdown
is not modeled in physically. As written before, the breakdown modeling
is based on two model parameters: the "nominal breakdown voltage" @option{BV}
and the current at the onset of breakdown @option{IBV}. For the diode
model to be consistent, the current value cannot be arbitrary choosen,
since the reverse bias and breakdown regions must match.
When the diode enters breakdown region from reverse bias, the current
is calculated using the formula:
@tex
$$
I_{bdwn} = -IS_{eff} ( e^{-q {\rm BV} \over N k T} - 1)
$$
@end tex
@ifnottex
@example
To be written!
@end example
@end ifnottex
@sc{Note:} if you look at the code in @file{diotemp.c} you will discover
that the exponential relation is replaced with a first order taylor
series expansion.
The computed current is necessary to adjust the breakdown voltage
making the two regions match. The algorithm is a little bit convoluted
and only a brief description is given here:
@tex
if $IBV_{eff} < I_{bdwn}$ then
$$ IBV_{eff} = I_{bdwn} $$
$$BV_{eff} = {\rm BV} $$
else
$$BV_{eff} = {\rm BV} - {\rm N} V_t \ln({ IBV_{eff} \over I_{bdwn}}) $$
@end tex
@ifnottex
@example
IF IBVeff < Ibdwm THEN
IBVeff = Ibwn
BVeff = BV
ELSE
BVeff = BV - N * Vt * LN(IBVeff/Ibdvn)
END IF
@end example
@end ifnottex
Most real diodes shows a current increase that, at high current levels,
does not follow the exponential relationship given above. This behavior
is due to high level of carriers injected into the junction. High
injection effects (as they are called) are modeled with @option{IK} and
@option{IKR}.
@tex
$$
I_{Deff} = \cases{ {{I_D} \over {1 + \sqrt{I_D \over IK_{eff} }}}, &if $V_D \geq -3{NkT \over q}$\cr
{{I_D} \over {1 + \sqrt{I_D \over IKR_{eff} }}}, &otherwise.\cr}
$$
@end tex
@ifnottex
@example
Not yet written!
@end example
@end ifnottex
Diode capacitance is divided into two different terms:
@itemize @bullet
@item Depletion capacitance
@item Diffusion capacitance
@end itemize
Depletion capacitance is composed by two different contributes, one
associated to the bottom of the junction (bottowall depletion capacitance)
and the other to the periphery (sidewall depletion capacitance).
The basic equations are:
@tex
$$
C_{Diode} = C_{diffusion} + C_{depletion}
$$
@end tex
@ifnottex
@example
Cdiode = Cdiffusion + Cdepletion
@end example
@end ifnottex
Where the depletion capacitance i defined as:
@tex
$$
C_{depletion} = C_{depl_{bw}} + C_{depl_{sw}}
$$
@end tex
@ifnottex
@example
Cdepletion = CdeplBW + CdeplSW
@end example
@end ifnottex
The diffusion capacitance, due to the injected minority carriers is
modeled with the transit time @option{TT}:
@tex
$$
C_{diffusion} = {\rm TT}{{\partial I_{Deff}} \over {\partial V_{D}}}
$$
@end tex
@ifnottex
@example
dIDeff
Cdiffusion = ----- * TT
dVd
@end example
@end ifnottex
The depletion capacitance is more complex to model, since the function
used to approximate it diverges vhen the diode voltage become greater
than the junction built-in potential. To avoid function divergence, the
capacitance function is approximated with a linear extrapolation for
applied voltage greater than a fraction of the junction built-in potential.
@tex
$$
C_{depl_{bw}} = \cases{ CJ_{eff}\cdot(1-{V_D \over {\rm VJ}})^{-{\rm MJ}}, &if $V_D < {\rm FC}\cdot{\rm VJ}$\cr
CJ_{eff}\cdot{{1 - {\rm FC}\cdot(1 + {\rm MJ}I) + {\rm MJ}\cdot{V_D \over {\rm VJ}}}\over{(1-{\rm FC})^{(1 +{\rm MJ})}}} , &otherwise.\cr}
$$
$$
C_{depl_{sw}} = \cases{ CJP_{eff}\cdot(1-{V_D \over {\rm PHP}})^{-{\rm MJSW}}, &if $V_D < {\rm FCS}\cdot{\rm PHP}$\cr
CJP_{eff}\cdot{{1 - {\rm FCS}\cdot(1 + {\rm MJSW}) + {\rm MJSW}\cdot{V_D \over {\rm PHP}}}\over{(1-{\rm FCS})^{(1 +{\rm MJSW})}}} , &otherwise.\cr}
$$
@end tex
@ifnottex
@example
Not yet written!
@end example
@end ifnottex

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