Parts Index
MicroSim Parts Help Contents

The index contains a list of all Help topics available for Parts  For information on how to use Help, press F1 or choose Using Help from the Help Menu.

Parts

Overview

Keyboard Commands

Menu Commands

Toolbar Commands

Spec Entry Help

Diode Spec Entry

BJT Spec Entry

JFETSpec Entry

Power MOSFET Spec Entry

Magnetic Core Spec Entry

Opamp Spec Entry

Voltage Comparator Spec Entry

Voltage Regulator Spec Entry

Voltage Reference Spec Entry


Parts Overview
Overview

One of the difficult areas in using analog circuit simulators is finding accurate models for off-the-shelf parts.  The Parts program is a semi-automatic aid for determining the model parameters for standard devices, such as bipolar transistors, and the subcircuit definitions for more complex models, such as operational amplifiers.  Parts allows you to convert information from the component manufacturer's data sheet (without taking measurements of a real device) into parameter values used by PSpice.  Once you have the parameter values, you can include the device as part of your own library of devices.

Now, you may ask, "Why do I need to model these devices?  Won't the data sheet values work?"  Well, yes and no.  Yes, for simpler devices such as resistors, which only need the resistance value to have a complete model.  No, for more complex devices, especially semiconductor devices.  This is because the physical model for predicting how a transistor operates views the transistor from the "inside," while the manufacturer provides measurements that show how the transistor operates from the "outside."  Therefore, a conversion is necessary from data sheet values to physical model parameters.

Data sheet information shows what the manufacturer will guarantee when you buy a part.  The device's operating characteristics will fall within the range specified: a particular part could be near the minimum value of one specification and near the maximum value of another.  A typical value is given for some specifications to indicate how most of the devices will operate.  Therefore, while Parts will work with measurements taken from a specific device, this is not necessary.  You will probably want to use typical values from the data sheet for most of your simulation work.  You may also want to create best/worst-case models for checking your design.

Note: Parts generated the device charcteristics curves by using a subset of the model parameters and with simplify approximation.  Some of these curves do not match exactly with Pspices simulation result.


Parts Function Keys

Press the key combination to directly invoke the menu item.

Ctrl+A	View/Area

Ctrl+B	Part/IBIS Translator

Ctrl+C	Part/Copy

Ctrl+D	Plot/Display

Ctrl+E	Extract/Parameter

Ctrl+F	File/Open or Create library

Ctrl+G	Part/Get

Ctrl+H	File/Print

Ctrl+I	View/In

Ctrl+K	Select next Parameter

Ctrl+L	View/Redraw

Ctrl+M	Part/Save

Ctrl+N	View/Fit

Ctrl+O	View/Out

Ctrl+P	View/Previous

Ctrl+Q	Edit/Spec

Ctrl+R	Edit/Parameter

Ctrl+S	File/Save Library

Ctrl+T	Trace/Add

Crtl+V	Select next Spec

Ctrl+X	Edit/Cut Trace

Ctrl+Y	Plot/Setting Y-Axis

Ctrl+Z	Plot/Setting X-Axis

Ins	Trace/Add

Del	Edit/Cut Trace


Parts Menu Commands
Menu Commands

The Parts commands allow you to create and edit parts from library/ASCII file, enter and modify specification, view plots, and perform model parameter extraction.

File Menu	Opens and saves library files and prints plots.

Edit Menu	Modifies specification, parameter, or deletes traces.

Part Menu	Opens and saves parts in memory and performs export/import parts to/from file.

Trace Menu	Allow user to add traces to the current plot.

Plot Menu	Sets up the display and hard copy environment.

View Menu	Changes the viewing scale on the schematic, redraw.

Extract Menu	Sets up the display and hard copy environment.

Options Menu	Sets up the toolbar display option.

Window Menu	Creates a netlist, sets up analyses, and runs simulations.

Help Menu	Provides context-sensitive help on all aspects of the schematic editor.


Parts Toolbar Commands
Toolbar Commands

The toolbar allows short cut to certain menu items.

	New allows you to create a new device model.  You must have a library open in order to create a new part.  The Create New Part dialog will appear prompting you for a part name and a part type.  Enter the name in the Part Name field and choose a part type from the Part Type field.  Scroll through the list box if needed to select an available template.  Click OK to end the dialog and begin entering the model specifications and parameters.  The default parameters will appear for the template chosen.  These default parameters are created by Parts.  Parts parameter defaults are different than PSpice default parameters.  Refer to the "Analog Devices" chapter for the default PSpice parameters..
	Get allows you to retrieve a part from a model library file.  A library file must be opened (File/Open) in order to get a part.  Scroll through the list to select a part, then click OK.  Once you get a part, this becomes the current part which is named in the title bar.
	Save allows you to save the current part to the opened library.  The current part name is displayed in the title bar at the top of the window.  All changes you have made up to this point have not been saved to the library yet.  You need to use File/Save to save the data on disk.
	Print allows you to print a copy of any or all of your plot windows.  At least one plot window must be selected, but all may be selected if desired.  (Note) no dialog box will appear, the selected plots will be printed to the printer.
	Display allows you to display one or more traces for the selected model parameters.  To display a trace, select a parameter from the Model Spec list box in the current device window, then chose Plot/Display.  To select more than one traces for display, click on the first model parameter, then <Shift>-click on one or more model parameters.  Select Display from the Plot Menu to view the traces.  Each trace will generate its own plot window.
	Zooms in by a factor of 2 around the point you specify with the mouse.
	Zooms out by a factor of 2 around the point you specify with the mouse.  The View/Fit limits will not be exceeded.  If the View/Fit limits are exceeded in either the X or Y direction, then only the direction in which they are not exceeded will zoom out by the full factor of 2.  The exceeded direction will only zoom out to the View/Fit limits..
	Causes the display to view into the area you specify with the mouse.  You specify this area by holding down the left mouse button and dragging the mouse.  This forms a window into which to view.  The area may be specified before or after the View/Area operation is selected.
	Sets the display back to the default view factor, and refreshes the display.
	Toggle the X-axis scale between Linear and Logarithmic. You cannot put the axis into a log scale if either end of the axis range is zero or negative
	Toggle the Y-axis scale between Linear and Logarithmic. You cannot put the axis into a log scale if either end of the axis range is zero or negative
	Starts the parameter extraction process.  Model parameters will be modified according to the specification data.  After parameter extraction is done, all plots will be updated to use the new model parameters.


Parts File Menu
File Menu

Opens and save files, establishes a new workspace, and prints copies of the schematic.  For more information, see the File Menu items in the list below:

Command	Description

Open/Create Library	Open/Create Library allows you to open or create a model library file.  You can create a new library or open an existing one using this command.  If you specify a file name in the Open Library dialog that does not exist, a new library will be created with the name you entered.

Save Library	Save Library saves the existing data and model parameters to the opened librarary.

Save As Library	SaveAs Library allows you to save the current data and model parameters to a new file, or overwrite an existing library file.

Print	Print allows you to print a copy of any or all of your plot windows.  When Print is selected, the Print dialog appears with a list box displaying a list of all plot windows that are currently open.  At least one plot window must be selected, but all may be selected if desired.  The Select All button can be used to quickly select all of the plot windows for print.

Page Setup	Page Setup allows you to set print related options.  The controls in this dialog allow you to change a variety of settings to alter the way the printed plots appear on the hard copy page.  The options available are dependent upon the printer you have selected (see Printer Select below).

Printer Select	Printer Select allows you to change the current default printer.  To select a printer other than the current default, use the Specific Printer pull-down and select one.

Log Commands	Log Commands allows you to turn command logging on and off.  Turning on command logging allows you to create a file of the commands that you will use.  This file can subsequently be used to play back those commands by using Run Commands.  When you first select Log Commands, you can enter a file name in which the commands will be stored.  From this point on, all actions taken in Parts will be stored in this log file.  In order to indicate that command logging is in progress, the Log Commands selection is marked with a check.  You may turn off command logging simply by selecting Log Commands again, which will also remove the check.

Run Commands	Run Commands allows you to play back a command file created with Log Commands.  You will choose a file from a dialog box showing the available command files.  The Run Command File dialog appears allowing you to select a command file to run.

Exit	Exits Parts and returns control to the Windows environment.

1-4	1-4 is a shortcut for opening one of the four most recently used library files.  The file name listed by 1 is for the most recently used file, and the file name by 4 is for the fourth most recently used file.


Parts Edit Menu
Edit Menu

Edits the graphics and part definition of the current part.  For more information, see the Edit Menu items in the list below:

Command	Description

Cut	Cut allows you to delete a selected trace.  Click on a trace name in the device curve plot window to select it, then select Cut to remove the trace from the plot.

Parameter	Edit Parameter allows you to edit the internal parameters of the model definition.  First select a model parameter from the Parameters list box located on the right-hand side of the main window.  Once the item is selected you can choose Edit/Parameter or you can double-click on the highlighted item to bring up the Edit Parameter dialog.  Edit the values in the fields provided, then click OK to save the modifications.  Click Cancel to disregard all actions.

To edit parameters you can specify an upper or lower boundary from which parameters will be extracted.  You can click in the Freeze current value from extraction check box to indicate that you want the to keep the current value as specified during parameter extraction.  For example, if the current value for EG (activation energy) is 1.110 and you click in this check box, then EG will maintain its value of 1.110 during parameter extraction.

Spec	Edit Spec allows you to modify the model specifications for the model template chosen.  For example, one of the model parameters for the diode template is Forward Current.  To edit the specification for forward current, select Forward Current in the left list box, then click select Edit/Spec.  Or, you can double-click on Forward Current to bring up the Edit Model Spec dialog.  Once in the dialog, Add, Modify, and Delete specification data as desired.  Click OK to save the changes, and click Cancel to disregard all actions.


Parts Part Menu
Part Menu

Command	Description

New	New allows you to create a new device model.  You must have a library open in order to create a new part.  The Create New Part dialog will appear prompting you for a part name and a part type.  Enter the name in the Part Name field and choose a part type from the Part Type field.  Scroll through the list box if needed to select an available template.  Click OK to end the dialog and begin entering the model specifications and parameters.

The default parameters will appear for the template chosen.  These default parameters are created by Parts.  Parts parameter defaults are different than PSpice default parameters.  Refer to the "Analog Devices" chapter for the default PSpice parameters..

Copy	Copy copies an existing part definition to a new part name in a user-selected library.  Enter a unique name for the new part in the New Part Name field.  You can select a part from the opened library by scrolling through the Part list and clicking on a part name.  Clicking on a part name will send the part name to the Existing Part Name field.  Click OK to copy the part definition to the new part name.

The opened library name will be displayed above the Select Lib button.  If no library is currently open, click Select Lib to browse and choose a library file to be opened.  (See Select Lib below.)

Select Lib allows you to browse through directories to select a library file.  Select a library file which contains the existing part you want to copy.  Click OK once you have chosen the desired file name.  Click Cancel to return to the Copy Part dialog.

Get	Get allows you to retrieve a part from a model library file.  A library file must be opened (File/Open) in order to get a part.  Scroll through the list to select a part, then click OK.  Once you get a part, this becomes the current part which is named in the title bar.

Save	Save allows you to save the current part to the opened library.  The current part name is displayed in the title bar at the top of the window.  All changes you have made up to this point have not been saved to the library yet.  You need to use File/Save to save the data on disk.

IBIS translator	IBIS translator allows you to translate a model definition in IBIS model format to a PSpice model definition.  The IBIS model must be saved in a ".ibs" file.  Once you select a file to be translated in the IBIS Translator dialog box, click OK.  A PSpice model file in a ".mod" format will be created in the same working directory.

Export	Export writes the part definitions from the current part to an ASCII text file and gives the exported file a ".mod" extension if no extension is specified.  This command allows you to transfer model definitions from one library to another.

Import	Import allows you to import part definitions from ".mod" files into the current model library.


Parts Trace Menu
Trace Menu

Command	Description

Add	Add allows you to add traces to an existing plot.  You must use Plot/Display to plot a curve.  The default trace variable in the device curve window is temperature.  You can specify a temperature in the Add Traces dialog for which you want to see the trace displayed.  For example, you may want to display the reverse drain current at 10 degrees. In this case you would enter 10 in the Temperature field of the Add Traces dialog, then click OK.  The trace displayed would be named Idr(10c).

Note that some traces will not have temperature effects.  Therefore changing the temperature value will not alter the trace.  To change the trace variable, select Plot/X Axis Settings/Trace Variable..


Parts Plot Menu
Plot Menu

Command	Description

Display	Display allows you to display one or more traces for the selected model parameters.  To display a trace, select a parameter from the Model Spec list box in the current device window, then chose Plot/Display.  To select more than one traces for display, click on the first model parameter, then <Shift>-click on one or more model parameters.  Select Display from the Plot Menu to view the traces.  Each trace will generate its own plot window.

X Axis Settings	X Axis Settings allows you to modify the X axis settings for the currently selected plot window.

Data Range	This sets the range of the X axis to your specification.  Once set, the range is not affected by changes in the axis' variable/traces.  It can only be changed by one of the view commands or another user defined range.

To enter a data range, enter the beginning value of the range in the first field, then enter the end value in the second field.  By specifying the correct units, you assure that the units will appear on the numbers labeling the axis' tick marks.

This command may be used to invert an axis.  For instance, instead of having a range of (0V to 5V), you can set the range to (5V to 0V).  All the traces on that axis are then inverted.

Scale	Linear sets the current X axis to linear.

Log sets the current X axis to logarithmic.  You cannot put the axis into a log scale if either end of the axis range is zero or negative

Trace Variable	allows you to modify the trace variable for the X axis for use with Trace/Add.  Click on the Trace Variable button, then select a variable from the list box.  Click OK to accept your changes, or click Cancel to dird.  The X axis will show which trace variable is being used.

Y Axis Settings	Y Axis Settings allows you to modify the Y axis settings.

Data Range	Auto Range sets the range of the Y axis to be the range of its variable/traces, rounded to a convenient value.  The range of the axis will be automatically adjusted as its variable/traces are changed.

User Defined sets the range of the Y axis to your specification.  Once set, the range is not affected by changes in the axis' variable/traces.  It can only be changed by one of the view commands or another User Defined command.

To enter a user-defined data range, enter the beginning value of the range in the first field, then enter the end value in the second field.  By specifying the correct units, you assure that the units will appear on the numbers labeling the axis' tick marks.

Scale	Linear sets the current Y axis to linear.

Log sets the current Y axis to logarithmic.  You cannot put the axis into a log scale if either end of the axis range is zero or negative.


Parts View Menu
View Menu

Changes the viewing scale on your plot.  For more information, see the View Menu items in the list below:

Command	Description

Fit	Sets the display back to the default view factor, and refreshes the display.

In	Zooms in by a factor of 2 around the point you specify with the mouse.

Out	Zooms out by a factor of 2 around the point you specify with the mouse.  The View/Fit limits will not be exceeded.  If the View/Fit limits are exceeded in either the X or Y direction, then only the direction in which they are not exceeded will zoom out by the full factor of 2.  The exceeded direction will only zoom out to the View/Fit limits..

Area	causes the display to view into the area you specify with the mouse.  You specify this area by holding down the left mouse button and dragging the mouse.  This forms a window into which to view.  The area may be specified before or after the View/Area operation is selected.

Previous	resets the display to the previous view.  Any time the view is changed (with View commands, User defined X Axis or Y Axis Settings, or with the scroll bars), the view is pushed onto the "view stack."  A view stack is a memory queue of display views.

There is one view stack per plot.  View changes for all Y axes for a plot go into the view stack for that plot

Redraw	Causes the active plot window to be redisplayed.

Pan-New Center	Allows you to change the center of the plot view without changing the scale of the plot.  To do this, select Pan - New Center, and click the mouse at the point on the plot that you want to be the center of the new view..


Parts Extract Menu
Extract Menu

Command	Description

Parameters	Starts the parameter extraction process.  Model parameters will be modified according to the specification data.  After parameter extraction is done, all plots will be updated to use the new model parameters.


Parts Toolbar Menu
Options Menu

Command	Description

Toolbar	Toggles the display of toolbar.


Parts Toolbar Menu
Window Menu

Command	Description

Close	Closes the current window.

Arrange	Allows you to arrange the plot windows by either cascading or tiling.

1-9	Brings the selected plot window to the foreground.


Parts Help Menu
Help Menu

The Help Menu provides context-sensitive help on all aspects of Parts.  For more information see the  Help Menu items in the list below:

Command	Description

Index	Lists the main topics available in the Help Menu.

Keyboard	Lists the function keys and shortcut commands.

Menu Commands	Provides help on all menu commands.

Using Help	Provides a tutorial on how to use this help system.

About	Displays the software version and customer ID#.


Parts Diode Spec Entry

Forward Current

Junction Capacitance

Reverse Leakage

Reverse Breakdown

Reverse Recovery


Parts BJT Spec Entry

Junction Voltage

Output Admittance

Forward Current

Vce(sat) Voltage

C-B Capacitance

E-B Capacitance

Storage Time

Gain Bandwidth


Parts JFET Spec Entry

Transconductance

Output Conductance

Transfer Curve

Reverse Transfer Capacitance

Input Capacitance

Passive Gate Leakage

Active Gate Leakage

Noise Voltage


Parts Power MOSFET Spec Entry

Transconductance

Transfer Curve

Rds(on) Resistance

Zero-Bias Leakage

Turn-On Charge

Output Capacitance

Switching Time

Reverse Drain Current


Parts Magnetic Core Spec Entry

Hysteresis Curve


Parts Opamp Spec Entry

Large Signal Swing

Open Loop Gain

Open Loop Phase

Maximum Output Swing


Parts Voltage Comparator Spec Entry

Transfer Function

Falling Delay

Transition Time

Rising Delay


Parts Voltage Regulator Spec Entry

Reference Voltage

Adjustment Pin Current

Output Impedance

Current Limit


Parts Voltage Reference Spec Entry

Reverse Dynamic Impedance

Reference Voltage

Temperature Drift

Reverse Characteristics

Forward Characteristics


Diode Forward Current
Diode - Forward Current

Device curve:

        Vfwd    forward voltage across junction for Ifwd

        Ifwd    forward current @ Vfwd

Model parameters:

        IS      saturation current

        N       emission coefficient

        RS      series resistance

        IKF     high-injection "knee" current

        XTI     IS temperature coefficient

        EG      activation energy

This specification estimates the parameters IS and RS from three voltage and current values.  Try to include data from low current values (where the increase in current is exponential), moderate current values, and high current value (where the increase in current is clearly resistive).

The model parameters, XTI and EG, may be changed.  We have set them to be normal values for silicon diodes.  For Schottky-barrier diodes these may be changed to XTI = 2 and EG = 0.69, which will give better modeling over temperature.

Also, it is sometimes helpful to set up traces for a few values of temperature (use Trace command) for adjusting XTI.


Diode Junction Capacitance
Diode - Junction Capacitance

Device curve:

        Vrev    reverse voltage across diode (junction) for Cj

        Cj      junction capacitance @ Vrev

Model parameters:

        CJO     zero-bias junction capacitance

        VJ      junction potential

        M       junction grading coefficient

        FC      coefficient for onset of forward-bias depletion capacitance

This screen estimates the parameters CJO and M from a capacitance values given at non-zero reverse biases (a zero value for a Vj data point is OK).

The value for FC has been set to be normal for silicon diodes, but is relatively unimportant, as forward capacitance is dominated by diffusion capacitance (and modeled by transit time).

The data sheets for most switching and power diodes have little detail about reverse bias capacitance, because it is not too important.  Varicap diodes usually have better, more complete information.  Be aware that the diode package adds some fixed amount of capacitance that is not included in the device model, but may be included by the user with a small capacitor across the diode.  Having determined the package capacitance, subtract that from the total capacitance to model the diode junction.


Diode Reverse Leakage
Diode - Reverse Leakage

Device curve:

        Vrev	reverse voltage for Irev

        Irev	reverse (leakage) current @ Vrev

Model parameters:

        ISR	recombination current saturation value

        NR	recombination current emission coefficient

This screen derives the generation-recombination current values for the device which, with the capacitance modeling (previous screen), provides the primary leakage mechanism of the diode junction.

Reverse current leakage is increased by imperfections in manufacturing which are not modeled.  Breakdown also increases reverse current, but this is modeled in the next screen.


Diode Reverse Breakdown
Diode - Reverse Breakdown

Device data:

        Vz      nominal Zener voltage @ Iz

        Iz      nominal Zener current for Vz

        Zz      Zener impedance (resistance) @ Vz,Iz

Model parameters:

        BV      reverse breakdown voltage (a positive value)

        IBV     reverse breakdown current (a positive value)

This screen estimates the parameters BV and IBV for reverse breakdown operation, which is how voltage regulator (Zener or avalanche) diodes work. Enter the values for Vz, Iz, and Zz.

BV and IBV will nearly equal Vz and Iz.  As the breakdown effect is modeled by an exponential function, the value of BV and IBV will adjust so that device impedance, Zz (ratio of the change in voltage to the change in current) is correct at Vz,Iz.


Diode Reverse Recovery
Diode - Reverse Recovery

Device data:

        Trr     reverse recovery time

        Ifwd    forward current (before switching)

        Irev    initial reverse current

        Rl      load resistance (total load of test fixture)

Model parameters:

        TT      transit time

This screen estimates the parameter TT from switching time.  Enter values for the upper list.  Be sure to include the test fixture resistance and pulse generator resistance in Rl.

The screen does a transient simulation of the diode switching.  Some of the parameters from earlier screens that have dynamic effects, for example, CJO, are included in the simulation.  You may need to adjust the X-axis to see the entire waveform.


JFET Transconductance
JFET - Transconductance

Device curve:

        Id      drain current for gFS

        gFS     forward transconductance @ Id

Model parameters:

        BETA    transconductance coefficient

        RD      drain resistance

        RS      source resistance

        BETATCE temperature coefficient for BETA

This screen estimates the parameter BETA, which sets the change in drain current vs. gate-source voltage.  BETATCE is set manually, using traces at other temperatures to judge the effect (the default setting is a nominal value chosen from inspecting many data sheets).

Also, it is sometimes helpful to set up traces for a few values of temperature (use Trace command) for adjusting BETATCE.


JFET Output Conductance
JFET - Output Conductance

Device curve:

        Id      drain current for gOS

        gOS     output conductance @ Id

Model parameters:

        LAMBDA  channel-length modulation

This screen estimates the parameter LAMBDA, which sets the slope of the drain current vs. drain-source voltage in saturation.


JFET Transfer Curve
JFET - Transfer Curve

Device curve:

        Vgs     gate-source voltage for Id (@ Vds)

        Id      drain current @ Vgs

Conditions:

        Vds     drain-source voltage for device curve

Model parameters:

        VTO     threshold voltage

        VTOTC   temperature coefficient for VTO

This screen estimates the parameter VTO, which is the threshold ("pinchoff") voltage.  VTOTC is set manually, using traces at other temperatures to judge the effect (the default setting is a nominal value chosen from inspecting many data sheets).

Note: The SPICE "standard" is for VTO to be a negative value for a depletion transistor, regardless of device type (NJF or PJF).


JFET Transfer Capacitance
JFET - Reverse Transfer Capacitance

Device curve:

        Vgs     gate-source voltage for Crss (@ Vds)

        Crss    reverse transfer capacitance @ Vgs

Conditions:

        Vds     drain-source voltage for device curve

Model parameters:

        CGD     zero-bias gate-drain capacitance

        M       junction grading factor

        PB      built-in potential

        FC      forward-bias coefficient

This screen estimates the parameters CGD and M.  The reverse transfer, or "Miller", capacitance is modeled.

The parameter FC applies to forward-biased junctions and is included for completeness.


JFET Input Capacitance
JFET - Input Capacitance

Device curve:

        Vgs     gate-source voltage for Ciss (@ Vds)

        Ciss    input capacitance @ Vgs

Conditions:

        Vds     drain-source voltage for device curve

Model parameters:

        CGS     zero-bias gate-source capacitance

This screen estimates the parameter CGS, which is derived from Ciss - Crss.  As a check, since most JFETs are designed to be symmetrical, the value found for CGS should be close to that found for CGD (previous screen).


JFET Passive Gate Leakage
JFET - Passive Gate Leakage

Device curve:

        Vdg     drain-gate voltage for Igss

        Igss    gate leakage current @ Vdg

Model parameters:

        ISR     recombination current saturation value

        NR      recombination current emission coefficient

        IS      junction saturation current

        N       junction emission coefficient

        XTI     IS temperature coefficient

This screen derives the generation-recombination current values for the device which, with the capacitance modeling (previous screens), provides the primary leakage mechanism of the device's junction.

Passive reverse current leakage is increased by imperfections in manufacturing and breakdown, which are not modeled.

Also, it is sometimes helpful to set up traces for a few values of temperature (use Trace command) for adjusting XTI.


JFET Active Gate Leakage
JFET - Active Gate Leakage

Device curve:

        Vdg     drain-gate voltage for Ig (@ Id)

        Ig      gate leakage current @ Vdg

Conditions:

        Id      drain current for device curve

Model parameters:

        ALPHA   impact ionization coefficient

        VK      ionization "knee" voltage

This screen estimates active gate current when the JFET is on, which may be much larger than when the JFET is cut off.

Impact ionization by drain-current carriers generate carriers in the gate space-charge region, which get swept out through the gate.  This causes gate current which is an exponential function of drain voltage and proportional to drain current.

Note that the lowest values of active leakage current are generally less than the passive leakage values (previous screen); this is because the passive values are measured with source and drain shorted together, which usually doubles the junction area and, thus, the current.  Active leakage current occurs in the drain-gate junction only, so the lowest levels represent passive leakage for that junction.


JFET Noise Voltage
JFET - Noise Voltage

Device curve:

        Freq    frequency for en (@ Ids)

        en      equivalent input noise voltage (in volts/root-hertz) @ Freq

Conditions:

        Ids     drain current for device curve

Model parameters:

        KF      flicker noise coefficient

        AF      flicker noise exponent

This screen estimates the parameter KF, to set the correct amount of flicker noise.  AF may be set manually but is normally close to 1.  The broadband noise of a JFET is "shot" noise and is set by the conductance of the channel.


Hysteresis Curve (K Device)
Nonlinear Magnetic Cores - Hysteresis Curve

Device curve:

        H       magnetic influence (in Oersteds)

        B       magnetic flux (in Gauss)

Conditions:

        æi      initial permeability

Model parameters:

        Ms      magnetization saturation

        A       thermal energy parameter

        C       domain flexing parameter

        K       domain anisotropy parameter

This screen estimates the bulk material parameters from the envelope of the B-H curve and the value for the initial permeability of the material.  The "initial" B-H curve, starting from the origin, is also shown but is characterized only by the value for initial permeability.

Unlike most screens in Parts, in this screen the extent of the X-axis plays a role in extracting the model parameters.  Owing to the hysteresis (memory) effects in magnetic materials, how the material behaves depends on, virtually, its entire history.  This means the B-H curve will depend on how strong a field it has been subjected to.  To accommodate this behavior, Parts simulates a range of fields with magnitudes up to the maximum extent displayed by the X-axis.  For example, if you set the X-axis for a range of -5 to +5, Parts will use fields in that range when extracting the model parameters; the same range of fields will also be used if you set the X-axis for a range of 0 to +5.  After you have fitted the parameters, you may change the X-axis to see the material's behavior under a different range of external fields.

Warning: numerous evaluations are made when extracting these model parameters.  Even the fastest computers will appear to stall, momentarily, while performing the extraction.


MOSFET Transconductance
Power MOSFET - Transconductance

Device curve:

        Id      drain current for gFS

        gFS     forward transconductance @ Id

Model parameters:

        KP      transconductance

        W       channel width

        L       channel length

        RS      source ohmic resistance

This screen estimates the basic geometry of the power MOSFET, its conductance parameter, and high-current effects of series resistance in the device.

Many general assumptions are made about the device structure (such as oxide thickness), but the model will remain accurate in spite of these assumptions.  The transconductance would ideally increase proportional to the square-root of the drain current, but is limited by the effects of RS.


MOSFET Transfer Curve
Power MOSFET - Transfer Curve

Device curve:

        Vgs     gate-source voltage for Id

        Id      drain current @ Vgs

Model parameters:

        VTO     zero-bias threshold voltage

This screen estimates the device threshold voltage.

The actual value of VTO is not as important as obtaining a good value of drain current vs. Vgs as the device will be used.  For library use, use a drain current close to the maximum continuous rating.


MOSFET Rds (On) Resistance
Power MOSFET - Rds(on) Resistance

Device data:

        Id      drain current for Rds

        Vgs   gate-source voltage for Rds

        Rds     static drain-source on-state resistance @ Id and Vgs

Model parameters:

        RD      ohmic drain resistance

This screen estimates the "on-resistance" of the device.

The MOS model has three contributions to the "on-resistance": the channel resistance of the device, and an ohmic resistance in series with each the source and the drain.  This screen adjusts RD so the total resistance is correct.  However, RD cannot become negative.  Rds should be taken at an Id value not to exceed the absolute maximum rating for continuous current.


MOSFET Zero-bias Leakage
Power MOSFET - Zero-bias Leakage

Device data:

        Vds     drain-source voltage for Idss

        Idss    zero gate voltage drain current @ Vds

Model parameters:

        RDS     drain-source shunt resistance (PSpice extension MOS model)

This screen estimates the drain-source leakage of the device.  This leakage is due primarily to surface effects and is modeled by a shunt drain-source resistance.  Enter the values for the upper list.


MOSFET Turn-On Charge
Power MOSFET - Turn-on Charge

Device data:

        Qgd     gate-drain charge to switch load, Id, using supply, Vdd

        Qgs     gate-source charge to start switching

        Vds     supply voltage for Qgd

        Id      load (drain) current

Model parameters:

        CGSO    gate-source overlap capacitance

        CGDO    gate-drain overlap capacitance

This screen estimates the device's stray capacitances associated with the gate. These capacitances, along with the channel capacitance, make up the amounts of charge required to switch the device.

The value Qgs is the amount of charge required to raise the gate-source voltage from zero to that required to support the load current.  Qgd is due to "Miller", or gate-drain, capacitance.

Note that the values of CGSO and CGDO are multiplied by the channel width to yield the actual value of the capacitance.


MOSFET Output Capacitance
Power MOSFET - Output Capacitance

Device data:

        Coss    output capacitance @ Vds

        Vds     drain-source voltage for Coss

Model parameters:

        CBD     zero-bias bulk-drain junction capacitance

        PB      bulk junction potential

        MJ      bulk junction grading coefficient

        FC      bulk junction forward-bias capacitance coefficient

This screen estimates the output capacitance of the device.

The output capacitance is usually not critical, being small enough when compared with the load currents that are controlled by the device.


MOSFET Switching Time
Power MOSFET - Switching Time

Device data:

        tf      fall time for switching load, Id, using supply, Vdd

        Id      load (drain) current for tf

        Vdd     supply voltage for tf

        Zo      input generator impedance

Model parameters:

        RG      gate ohmic resistance

This screen estimates the value of series gate resistance from switching time.

Most power MOSFET devices use a self-aligned process with polysilicon gate material.  The polysilicon impedes the gate current, reducing the charging rate of the gate, which increases the turn-on time.  While there are many switching times specified (turn-on delay, rise time, etc.), they are all related by the parasitic capacitances, which have already been determined in the "gate charge" screen.  Only the series resistance needs to be determined, which can be done reliably with the fall time characteristic.

Note that "fall time" means the period in which the drain current is "falling" in value, not the output voltage.


MOSFET Reverse Drain Current
Power MOSFET - Reverse Drain Current

Device curve:

        Vsd     diode (source-drain) forward voltage for Idr

        Idr     reverse drain current @ Vsd

Model parameters:

        IS	bulk junction saturation current

        N       bulk junction emission coefficient

        RB      bulk series resistance

This screen estimates the forward voltage drop of the "body" diode.

The actual value of IS is not so important as obtaining a good value of voltage drop vs. current as the device will be used.


Bipolar Transistor Junction Voltage
Bipolar Transistor - Junction Voltage

Device data:

        Vbe     base-emitter voltage @ Ib (device in saturation)

        Vce     collector-emitter voltage (device in saturation)

        Ib      base current for Vbe and Vce

        %Ib     fraction of Ib (not a data sheet value)

Model parameters:

        IS      saturation current

        XTI     temperature coefficient for IS

        EG      activation energy

This screen estimates the parameter IS from the saturation characteristics of the transistor.  IS is a semiconductor junction parameter and should not be confused with the collector current in saturation.  The data sheet will have values or curves for Vbe and Vce in a "forced beta" (where the ratio Ic/Ib is much lower than the normal current gain) or "saturated" condition.  Enter values of Vbe and Vce for the same Ib.

The value of %Ib is a "fudge" value and is not critical.  It factors how much of the base current will be shunted through the ideal diode of the Gummel-Poon transistor model.  We have set it to a "normal" amount.

Obtaining an accurate value for IS is not critical, since other parameters will be set relative to IS, and only the ratio between values will be important.  It is necessary, though, to not have a wildly inaccurate value.  The last two model parameters, XTI and EG, may be changed.  We have set them to be normal values for silicon transistors.

The display graphs for this screen are not too useful.  However, they do let you know something is happening.


Bipolar Transistor Output Admittance
Bipolar Transistor - Output Admittance

Device curve:

        Ic      collector current for hoe

        hoe     small-signal open-circuit output admittance @Ic (and @Vce)

Conditions:

        Vce     collector-emitter voltage for the device curve

Model parameters:

        VAF     forward Early voltage

This screen estimates the parameter VAF, which sets the output conductance of the transistor in a common emitter configuration.

The parameter VAF controls one aspect of basewidth modulation in the Gummel-Poon transistor model.  This manifests itself as output conductance.  Typical values are 50-to-100 volts for normal transistors and 1-to-10 volts for super-beta transistors.


Bipolar Transistor Forward DC Beta
Bipolar Transistor - Forward DC Beta

Device curve:

        Ic      collector current for hFE (@ Vce)

        hFE     forward DC beta @ Ic

Conditions:

        Vce     collector-emitter voltage for the device curve

Model parameters:

        BF      ideal maximum forward beta

        ISE     non-ideal base-emitter diode saturation current

        NE      non-ideal base-emitter diode emission coefficient

        IKF     forward beta roll-off "knee" current

        NK      forward beta roll-off slope exponent

        XTB     forward beta temperature coefficient

This screen estimates parameters for the celebrated Gummel-Poon bipolar transistor model.  Try to include data from low current values (beta rising), moderate current values, and high current value (beta falling).  The value Vce adjusts the beta data for basewidth modulation effects.

Transistor data sheets usually show minimum beta values and have a maximum value for only one collector current value.  One way to obtain an average value is to use the current level that specifies both minimum and maximum beta, using a value somewhat below the average of the minimum and maximum.  Then ratio the other minimum values by the same amount.  Or just use the curves (if available) from the data sheet.

The value for XTB has been set to be normal for bipolar transistors but may be changed.  It is sometimes helpful to set up traces for a few values of temperature (use Trace command) for adjusting XTB.


Bipolar Transistor VCE(sat) Voltage
Bipolar Transistor - Vce(sat) Voltage

Device curve:

        Ic      collector current for Vce (@ Ib/Ic)

        Vce     collector-emitter voltage @ Ic

Conditions:

        Ic/Ib   "forced beta" ratio for device curve

Model parameters:

        BR      ideal maximum reverse beta

        ISC     non-ideal base-collector diode saturation current

        NC      non-ideal base-collector diode emission coefficient

        IKR     reverse beta roll-off "knee" current

        RC      series collector resistance

This screen estimates more parameters for the Gummel-Poon transistor model.  Try to include data from low current values (Vce falling), moderate current values, and high current value (Vce rising).  Also, be sure to check/enter the value for the "forced beta" ratio of collector to base current.

The reverse Gummel-Poon parameters correspond to the forward parameters, except they are for reverse operation (that is, emitter swapped with the collector). It would be more accurate to obtain these the same way as the forward parameters, but reverse operation is rarely published data.  Fortunately, it does not affect operation when the transistor is saturated, that is, when the base-collector junction is forward biased.


Bipolar Transistor C-B Capacitance
Bipolar Transistor - C-B Capacitance

Device curve:

        Vcb     reverse voltage collector-base junction for Cobo

        Cobo    open circuit output capacitance @ Vcb

Model parameters:

        CJC     0-bias collector-base junction capacitance

        VJC     collector-base junction potential

        MJC     collector-base junction grading coefficient

        FC      coefficient for onset of forward-bias depletion capacitance

This screen estimates the parameters CJC and MJC from capacitance values given at non-zero reverse biases (a zero value for Vcb is OK).

The value for FC has been set to be normal for silicon transistors but may be changed.  The value of FC is relatively unimportant, as forward capacitance is dominated by diffusion capacitance (and modeled by transit time).

Be aware that the transistor package adds some fixed amount of capacitance that is not included in the device model, but may be included by the user with a small capacitor across the junction.  Having determined the package capacitance, subtract that from the total capacitance to model the junction.


Bipolar Transistor E-B Capacitance
Bipolar Transistor - E-B Capacitance

Device curve:

        Veb     reverse voltage emitter-base junction for Cibo

        Cibo    open circuit input capacitance @ Veb

Model parameters:

        CJE     zero-bias emitter-base junction capacitance

        VJE     emitter-base junction potential

        MJE     emitter-base junction grading coefficient

This screen estimates the parameters CJE and MJE from capacitance values given at non-zero reverse biases (a zero value for Veb1 is OK).

The value of FC from the previous screen is used and is still relatively unimportant, as forward capacitance is dominated by diffusion capacitance.

Be aware that the transistor package adds some fixed amount of capacitance that is not included in the device model, but may be included by the user with a small capacitor across the junction.  Having determined the package capacitance, subtract that from the total capacitance to model the junction.


Bipolar Transistor Storage Time
Bipolar Transistor - Storage Time

Device curve:

        Ic      collector current for ts (@ Ic/Ib)

        ts      storage time (not "shelf life") @ Ic

Conditions:

        Ic/Ib   "forced beta" ratio for device curve

Model parameters:

        TR      reverse transit time

This screen estimates the parameter TR, which controls the delay until the transistor leaves saturation when switching off.  Be sure to check/enter a value for the "forced beta" ratio when the transistor was on and saturated.

The storage time curve is controlled by the forward and reverse beta characteristics of the transistor.  The parameter TR acts like a multiplying factor without changing the character of the curve.  Use the storage time for the collector current range you are interested in.


Bipolar Transistor Gain Bandwidth
Bipolar Transistor - Gain Bandwidth

Device curve:

        Ic	collector current for fT (@ Vce)

        fT	frequency at which small-signal forward current transfer ratio extrapolates to unity @ Ic

Conditions:

        Vce	collector-emitter voltage for device curve

Model parameters:

        TF	forward transit time

        ITF	current for TF dependency on Ic

        XTF	coefficient for TF dependency on Vce

        VTF	voltage for TF dependency on Vce

This screen estimates the parameter TF, which, along with collector-base capacitance, limits high-frequency gain.  The value of TF also controls rise/fall times in switching circuits, which is another way to measure transistor speed, though we haven't thought of a rule-of-thumb conversion between rise/fall time and high-frequency cutoff.

Also, it is sometimes helpful to set up traces for a few values of Vce (use Trace command) for adjusting VTF.


Operational Amplifier Large Signal Swing
Operational Amplifier - Large Signal Swing

Device data:

        +Vpwr   positive power supply

        -Vpwr   negative power supply

        +Vout   maximum positive output swing

        -Vout   maximum negative output swing

        +SR     positive-going slew-rate limit

        -SR     negative-going slew-rate limit

        Pd      quiescent power dissipation

Macromodel internal parameters:

        VC      output limiter offset (to Vcc)

        VE      output limiter offset (to Vee)

This screen sets the value of output voltage limiters but also gathers information that will be useful in later screens.  The graph shows the largest amplitude output a sinewave signal can be for a given frequency to have no distortion.  This is limited by the amplifier's output swing and slew-rate.

Power supply values: These are the data sheet values used in conjunction with the maximum output values and are not the power supply values for the circuit simulation (which may be different).  The opamp model limits the output swing by an amount relative to the power supply, so the output swing limit will track the power supply in the simulation.

Slew-rates: Since Parts uses primary units (e.g., volts, amps, farads, etc.), the variety of ways of specifying slew-rate needs to be converted to volts/second, for example, 5V/uS is 5,000,000 V/S.


Operational Amplifier Open Loop Gain
Operational Amplifier - Open Loop Gain

Device data (BJT-input):

        Cc      compensation capacitor

        Ib      input bias current

        Av-dc   open-loop gain (DC)

        f-0db   unity gain frequency

        CMRR    common-mode rejection ratio

Macromodel internal parameters:

        BF      input transistor beta

        C2      compensation capacitor

        CEE     slew-rate limiting capacitor

        GA      interstage transconductance

        GCM     common-mode transconductance

        IEE     input stage current

        RC      input stage load resistance

        RE      input stage emitter resistance

        REE     input stage current source output resistance

        RP      power dissipation

This screen completes the input stage and inner stage.  The compensation capacitor value (Cc) is sometimes available on the data sheet in the circuit diagram of the opamp.  If not, 20-to-30pF is a fair value.  For opamps with external compensation, use one of the values on the data sheet for the external capacitor.  Then be sure to use that value for the other input data.

About open-loop gain: this is a ratio of input/output signal, i.e., small-signal amplification.  Being a pure number, it has no units.  If the gain is specified as 20V/mV, the gain is 20,000; if the gain is spec'd as 90db, put in 90db (Parts converts xdb to 10x/20).

Unity gain frequency: This frequency is the intersection of a straight-line extension of the of the mid-band, open-loop, gain roll-off to unity gain (zero decibel).  The graph will show gain with only the low-frequency pole included.  The high-frequency pole is calculated from open-loop phase margin.

CMRR has no frequency dependence.

For Device data (JFET-input):

        Cc      compensation capacitor

        Ib      input bias current

        Av-dc   open-loop gain (DC)

        f-0db   unity gain frequency

        CMRR    common-mode rejection ratio

Macromodel internal parameters:

        BETA    input transistor transconductance

        C2      compensation capacitor

        CSS     slew-rate limiting capacitor

        GA      interstage transconductance

        GCM     common-mode transconductance

        IS      input leakage current

        ISS     input stage current

        RD      input stage load resistance

        RP      power dissipation

        RSS     input stage current source output resistance

This screen completes the input stage and inner stage.  The compensation capacitor value (Cc) is sometimes available on the data sheet in the circuit diagram of the opamp.  If not, 10-to-20pF is a fair value.  For opamps with external compensation, use one of the values on the data sheet for the external capacitor.  Then be sure to use that value for the other input data.

Open-loop gain: This is a ratio of input/output signal, i.e., small-signal amplification.  Being a pure number, it has no units.  If the gain is spec'd as 20V/mV, the gain is 20,000; if the gain is specified as 90db, put in 90db (Parts converts xdb to 10x/20).

Unity gain frequency: This frequency is the intersection of a straight-line extension of the of the mid-band, open-loop, gain roll-off to unity gain (zero decibel).  The graph will show gain with only the low-frequency pole included.  The high-frequency pole is calculated from open-loop phase margin.

CMRR has no frequency dependence.


Operational Amplifier Open Loop Phase
Operational Amplifier - Open Loop Phase

Device data:

        Phi     phase margin (in degrees) @ unity gain frequency

Macromodel internal parameter:

        C1      phase control capacitor

This screen adjusts the open-loop unity-gain phase margin, which models the high-frequency pole.  Sometimes this value is not available in a table but can be found from a graph.  This value is not critical for lower-frequency circuits or lower-Q filters: just use the value we provided, which is typical for normal opamps.


Operational Amplifier Maximum Output Swing
Operational Amplifier - Maximum Output Swing

Device data:

        Ro-dc   DC output resistance

        Ro-ac   AC output resistance

        Ios     short-circuit output current limit

Macromodel internal parameters:

        RO1     output resistor #1

        RO2     output resistor #2

        GB      output stage transconductance

This screen adjusts the output drive.  The graph shows the maximum output level for a resistive load.  The data sheet usually lists an output resistance Ro = Ro-dc + Ro-ac.  Split this value so that Ro-dc is about 2 x Ro-ac.


Voltage Comparator Transfer Function
Voltage Comparator - Transfer Function

Device data:

        +Vpwr   positive power supply

        -Vpwr   negative power supply

        +Vicr   positive common-mode range

        -Vicr   negative common-mode range

        Ib      input bias current

        Avd     DC gain

        Rl      output load resistance

        Pd      power dissipation

Macromodel internal parameters:

        BF1     input stage gain

        BF5     output stage gain

        RP      power dissipation resistance

        VI      input offset

This screen sets gain values and an input offset (to model comparators whose common-mode input includes ground).  The screen shows the transfer function, usually un-informative, except to let you know something is happening.

About power supply values: these are the data sheet values used in conjunction with the maximum output values, and are not the power supply values for the circuit simulation (which may be different).


Voltage Comparator Falling Delay
Voltage Comparator - Falling Delay

Device data:

        Vst     input voltage step size

        Vod     input voltage step overdrive

        td      delay time

Macromodel internal parameter:

        TR3     input stage reverse transit time

This screen sets reaction time to input signals.  The data sheet usually gives "falling delay" which includes some of the transition in the output waveform (from 100% to 90%).  Usually the transition is much faster than the delay and can be ignored (or subtracted from the value).  The precise value is not critical given the unit-to-unit variation.


Voltage Comparator Transition Time
Voltage Comparator - Transition Time

Device data:

        Vst     input voltage step size

        Vod     input voltage step overdrive

        ttr     transition time

Macromodel internal parameter:

        TF5     output transistor forward transit time

This screen sets the "slew-rate" of the output.  The data sheet usually gives a value going from 90% to 10%, which will be within 25% of the full swing time. The precise value is not critical given the unit-to-unit variation.


Voltage Comparator Rising Delay
Voltage Comparator - Rising Delay

Device data:

        Vst     input voltage step size

        Vod     input voltage step overdrive

        td      delay time

Macromodel internal parameter:

        TR5     output transistor reverse transit time

This screen sets the reaction to input signals, but in the opposite direction. The data sheet usually gives "rising delay", which includes some of the transition in the output waveform (from 0% to 10%).  Usually the transition is much faster than the delay and can be ignored (or subtracted from the value). The precise value is not critical given the unit-to-unit variation.


Voltage Regulator Reference Voltage
Voltage Regulator - Reference Voltage

Device Data:

        Vref        reference voltage

Conditions:

        Dropout     dropout voltage

        (Vi-Vo)max  maximum input-output voltage differential

        IOmin       minimum output current to maintain regulation

Model Parameters:

        VREF        reference voltage

        N           emission coefficient

This screen shows the reference voltage across the output (OUT) pin and adjustment (ADJ) pin as the input-output voltage differential increases from 0V to (Vi-Vo)max.  The parameter (Vi-Vo)max is used for graphing purposes only.  It does not affect the model characteristics.

The dropout voltage specifies the minimum input-output voltage differential below which the circuit ceases to regulate.  This parameter is either obtained from the condition of the reference voltage parameter or is given as a parameter by itself in datasheets.

The minimum output current parameter is obtained from the condition of the reference voltage parameter in datasheets.  Be careful that this parameter is also given at the condition Vi-Vo=(Vi-Vo)max.  Do not use this value.


Voltage Regulator Adjustment Pin Current
Voltage Regulator - Adjustment Pin Current

Device Data:

Iadj        adjustment pin current

Model Parameter:

BETA        transconductance of JFET transistor

This screen displays the adjustment pin current as the input voltage increases from 0V to (Vi-Vo)max.  The parameter (Vi-Vo)max is used for graphing purposes only.  It does not affect the model characteristics.

The adjustment pin current represents an error term in the design equation:

Vo = Vref ( 1 + R2/R1 ) + Iadj * R2

where R1 and R2 are two external resistors.  Usually, Iadj is small such that the voltage Iadj*R2 is negligible in the above equation.


Voltage Regulator Output Impedance
Voltage Regulator - Output Impedance

Device Data:

Zout        low frequency output impedance

Zero        dominant zero frequency of output impedance

RR          low frequency ripple rejection in decibels.

Conditions:

Frequency   frequency at which Zout and RR are obtained

IO          output current at which Zout and RR are obtained

Model Parameters:

VAF         Early voltage of output pass transistor

CPZ         output impedance zero capacitor

This screen calculates the output impedance over frequency.  The output impedance is the impedance seen looking back into the OUT pin, excluding the effects of any external components connected to it.  Datasheets usually present the output impedance graphically.  Obtain Zout at the same frequency where the ripple rejection value is given.  Assume there is no capacitance connected to the adjustment pin (Cadj=0).

The condition Frequency is used for parameter referencing purposes only.  It does not affect the model characteristics.


Voltage Regulator Current Limit
Voltage Regulator - Current Limit

Device Data:

IOmax       maximum output current

Device Curve:

Iofb        foldback current

Vi-Vo       input-output voltage differential

Model Parameters:

RB2         base resistance of output pass transistor

ESC1        coefficient of current limit voltage source

ESC2        coefficient of current limit voltage source

EFB1        coefficient of foldback current voltage source

EFB2        coefficient of foldback current voltage source

EFB3        coefficient of foldback current voltage source

EB          first stage voltage gain

This screen shows the output current as the voltage Vi-Vo increases from 0V to (Vi-Vo)max as given in voltage reference screen when the output is shorted to ground.

The foldback current is the current when the maximum output current is reduced with increasing Vi-Vo voltage.  This current is shown as part of the current limit graph given in datasheets.  Parts performs a quadratic curve fit on the given data points of the foldback current.


Voltage Reference Reverse Dynamic Impedance
Voltage Reference - Reverse Dynamic Impedance

Device Curve:

Ir	reverse current

Rz	dynamic impedance

Model Parameters:

NZ	reverse breakdown coefficient

RZ	dynamic impedance

This screen shows the reverse dynamic impedance with reverse current at a low frequency.  The dynamic impedance is the impedance seen looking into the cathode terminal at a given reverse current.

Datasheets usually present the reverse dynamic impedance characteristics graphically.  Obtain Rz at nominal temperature.  Ir requires positive values.


Voltage Reference Reference Voltage
Voltage Reference - Reference Voltage

Device Data:

Vref	reverse breakdown voltage

Ir	reverse current at which Vref is obtained.

Irmax	absolute maximum reverse breakdown current

Model Parameters:

RBV	reverse breakdown reference resistance

IRMAX	absolute maximum reverse breakdown current

This screen displays the reverse characteristics as the reverse current increases to the absolute maximum breakdown current.  The portion of the curve below Vref is shown as an approximation here.  It is more accurately modeled in the Reverse Characteristics screen.

The reverse breakdown voltage is the reference voltage which exhibits tight tolerance and low temperature drift.  Obtain Vref at nominal operating temperature at Ir.  Datasheets usually give Irmax under the absolute maximum ratings section.  Vref requires positive values.


Voltage Reference Temperature Drift
Voltage Reference - Temperature Drift

Device Curve:

Temp	operating temperature in degrees Celsius

Vref	reverse breakdown voltage at Temp

Model Parameters:

TC1	first-order temperature coefficient

TC2	second-order temperature coefficient

This screen shows the reverse breakdown voltage variation with temperature at the reverse current Ir provided in the previous Reference Voltage screen.  The curve will pass through Vref at nominal temperature as specified in the previous Reference Voltage screen.

Parts does a quadratic curve fit to the given data points.  If temperature drift is not shown graphically in datasheets and only the average temperature coefficient is provided, enter data points such that the maximum deviation of Vref divided by the maximum temperature range will result in the correct average temperature coefficient.


Voltage Reference Reverse Characteristics
Voltage Reference - Reverse Characteristics

Device Curve:

Vr	reverse voltage

Ir	reverse current

Model Parameters:

IREV	reverse saturation current

NREV	reverse current coefficient

This screen shows the reverse characteristics for reverse voltages up to Vref.  See the Reference Voltage screen for voltages greater than Vref.

Datasheets usually show the reverse characteristics graphically.  Obtain data points at nominal temperature.  Both Vr and Ir require positive values.


XVoltage Reference Forward Characteristics
Voltage Reference - Forward Characteristics

Device Curve:

Ifwd	forward current @ Vfwd

Vfwd	forward voltage across junction for Ifwd

Model Parameters:

IS	saturation current

N	emission coefficient

RS	series resistance

IKF	high-injection "knee" current

XTI	IS temperature coefficient

This screen estimates the parameters IS and RS from three voltage and current values.  Try to include data from low current values (where the increase in current is exponential), moderate current values, and high current value (where the increase in current is clearly resistive).

Also, it is sometimes helpful to set up traces for a few values of temperature (use Trace command) for adjusting XTI.