Bias Point Display

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Bias Point Display Reference Guide

Product Version 16.0June 2007


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19962007 Cadence Design Systems, Inc. All rights reserved.Portions Apache Software Foundation, Sun Microsystems, Free Software Foundation, Inc., Regents ofthe University of California, Massachusetts Institute of Technology, University of Florida . Used bypermission. Printed in the United States of America.

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June 2007 5 Product Version 16.0

Bias Point Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

How bias information is stored and updated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Bias point data for multiple analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Displaying bias point values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Controlling the display of bias points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Moving bias points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Updating bias point values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Menu commands for bias point display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Toolbar controls for bias point display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Toggling a specic current bias display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Toggling a specic voltage bias display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Differences between bias point display in Capture vs. PSpice Schematics . . . . . . . . . . . 17

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Contents


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Bias Point Display Reference GuideBias Point Display


For currents on pins, a "+" value for the bias point means current is owing into the pin, whilea "-" value means current is owing out of the pin. By default, only voltages are displayed. Youcan toggle the currents on or off by using the corresponding toolbar buttons or menucommands.

How bias information is stored and updated

Not all pins and nets will have bias information. Buses, for example, do not have biasinformation, since they are not distinct wires. Bias point data and the locations of thedisplayed values are saved as part of the schematic page. Distinct bias point information issaved for each simulation prole. The data is updated whenever you open a schematic page,when you resimulate, when you activate a different simulation prole, or when you change thedisplay characteristics of the labels (such as color, font or precision).

For a schematic containing multiple pages, the bias information is stored with each page. Ifyou turn off bias point display on one page, this will not affect the display on other pages. If apage is reused (hierarchical subcircuits), the position of the bias point will be stored with thepage and will be the same for all occurrences of that page, although the values will bedifferent for each to accurately reect the hierarchy of the circuit.

Bias point data for multiple analyses

If you have set up more than one analysis, you should keep in mind the following:

Capture will always display the bias information for the last analysis you ran. PSpice runsanalyses in this order: DC, AC, Transient. This means that if you perform a multi-runanalysis like Parametric, Monte Carlo, Sensitivity/Worst-case or Temperature, you willsee bias values for the last run only.

A given voltage or current source can have a different DC value and initial transient valueat TIME=0. This means that the initial transient bias calculation can be different from theDC (small-signal) bias point.

For a Transient analysis, only the initial transient bias values are shown.

Displaying bias point values

You have the option of enabling the display of bias information for all nets and pins in thecircuit, or of enabling only selected nets and pins. You can also disable bias point display alltogether for situations such as large digital designs where the legibility of the schematic mightbe reduced.


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To enable or disable the display of all bias information

1. In Capture, from the PSpice menu, choose Bias Points. A submenu appears (see gure).

2. From the submenu, select Enable.

By clearing this option, you disable the bias display feature entirely. The presence of thecheck mark indicates that this option is enabled. (The default setting is to have this optionenabled.)

To enable or disable the display of all current bias points

1. In Capture, from the PSpice menu, choose Bias Points. A submenu appears.

2. From the submenu, select Enable Bias Current Display.

-or-

Click the toolbar button ( )

By checking this option, you enable the current bias display feature. The presence of thecheck mark indicates that this option is enabled. (The default setting is to have this optiondisabled.)


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Note: Enabling current bias display simply allows the feature to work, displaying whatevercurrent bias values were previously selected and toggled on. To learn how to toggle on or off

just one specic current bias display, click Toggling a specic current bias display.

To enable or disable the display of all voltage bias points


2. From the submenu, select Enable Bias Voltage Display.

-or-

Click the toolbar button ( )

By clearing this option, you disable the voltage bias display feature. The presence of thecheck mark indicates that this option is enabled. (The default setting is to have this optionenabled.)

Note: Enabling voltage bias display simply allows the feature to work, displaying whatevervoltage bias values were previously selected and toggled on. To learn how to toggle on or offall voltage bias displays, regardless of their previous settings, click Toggling a specic voltagebias display.

To turn on or off the display of selected current bias points

1. In Capture, click on a pin, or hold the CTRL key and click on several pins to select them.You can also click on a part to select all of the pins for that part.

2. From the PSpice menu, choose Bias Points. A submenu appears.

3. From the submenu, select Toggle Selected Bias Current.

-or-

Click the toolbar button ( ) after selecting the pins.

The presence of the check mark indicates that this option is turned on. (The default setting isto have this option turned off.)

Note: You can also turn off selected bias points by pressing the DELETE key. If you use theDELETE key, the bias point labels will be restored to their default locations the next time youdisplay them.


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Important

Since the current bias point of a capacitor equals zero, you will not see current biaspoint displays for these devices. Similarly, for other two terminal devices such asresistors, the current bias point will only be displayed on the positive (+) pin, becausethe negative (-) pin does not have a bias point value to display.

To turn on display of bias points after turning off selected bias point displays

1. From the Edit menu, choose Select All.

2. Click the toolbar button three times: Once to toggle on the bias displays that werepreviously turned off; once more to turn off all bias displays, and a third time to turn themall back on.

Controlling the display of bias points

You can set the precision of the bias point value that is displayed, and you can change thecolor or font of the label. You can also dene whether bias point data should be printed withthe schematic. These settings are all dened using the Bias Point Preferences dialog box(see gure below).

To set the precision of the bias point values:



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2. From the submenu, select Preferences. The Bias Point Preferences dialog box appears.

3. In the Displayed Precision text box, enter the number of decimals you wish to display for

the bias point values.4. Click OK.

This setting applies globally to all current and voltage bias points in your design. (The defaultsetting is 4.)

To set the color of the bias point values:



3. Click in the Color box for either Current or Voltage and select the color you wish to displayfrom the color palette.

4. Click OK.

These settings apply globally to all current and voltage bias points in your design.

To set the fonts for the bias point values:



3. Click in the Font box for either Current or Voltage and select the font type, style, and sizeyou wish to display from the font dialog box.

4. Click OK.

These settings apply globally to all current and voltage bias points in your design. (The defaultsetting is Arial 7.)

To print the bias point values: 1. In Capture, from the PSpice menu, choose Bias Points. A submenu appears.


3. Click the Print check box for either Current or Voltage. The bias point values will then printwith the schematic page.


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4. Click OK.

These settings apply globally to all current and voltage bias points in your design. The

presence of the check mark indicates that this option is enabled. (The default setting is tohave this option enabled.)

Moving bias points

Bias points have a default position near their corresponding wire or pin. You can select thebias point labels and relocate them to make the schematic page more legible. A dashedleader line extends from the label to the wire or pin it is associated with to indicate where thelabel belongs.

To move a bias point label:

1. Click on the label you wish to move to select it.

2. While holding down the left mouse button, drag the label to the new location.

Once you move a label, the new location will be saved with the schematic page so the biaspoint will be displayed there again the next time you open that page.

Updating bias point values

The bias point values displayed in Capture reect the data from the last simulation that wasperformed in PSpice. In some cases, these may not be the most recent values, depending onwhen they were last updated. There are three ways to update the values.

To update the bias point values by resimulating:

In Capture, from the PSpice menu, choose Run.

By re-running the simulation in PSpice, you update the bias points to the correct values.

To update the bias point values by changing proles:

1. In Capture's Project Manager, under the File tab, double-click on the Simulation Prolesfolder to see all the dened proles for this project.

2. Right-click on the prole you want to make active. A shortcut menu appears.


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3. From the shortcut menu, select Make Active.

By opening a new simulation prole, you update the bias points to reect the correct values

that were last calculated for that prole.

To update the bias point values by changing the display:



3. Click OK without changing any settings.

By opening the Preferences dialog box, you force Capture to update the bias points with the

correct values.

Menu commands for bias point display

The following table explains the menu commands for bias point display. You can access thesecommands by selecting Bias Points from the PSpice menu in Capture.

To see a map of these commands as they appear under the PSpice menu in Capture, clickBias Point menu.

Menu command... Function...

Enable Enables or disables the bias point display capability.

Enable Bias Current Display Enables or disables the display of current bias points for allmodeled pins in the entire design.

Toggle Selected Bias Current Turns on or off the display of current bias points for selectedmodeled pins.

Enable Bias Voltage Display Enables or disables the display of voltage bias points for allwires in the entire design.

Toggle Selected Bias Voltage Turns on or off the display of voltage bias points for selectedwires.

Preferences Provides controls for displaying the precision, color, font andprintability of the bias point values.


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Important

In order to access the PSpice menu in Capture, you must be working with a projectthat can be simulated. You must create a project (not a design) and select theAnalog or Mixed-Signal Circuit Wizard option in order to be able to simulate thedesign with PSpice.

Toolbar controls for bias point display

The following table explains the control buttons in the Bias Point toolbar.

The Bias Point toolbar in Capture

Toolbar Icon Description

Enable BiasVoltage Display

Enables or disables the display of voltage bias points for all wiresin the entire design.

ToggleSelectedBias Voltage

Turns on or off the display of voltage bias points for selectedwires.

Enable BiasCurrent Display

Enables or disables the display of current bias points for allmodeled pins in the entire design.

ToggleSelected

Bias Current

Turns on or off the display of current bias points for selectedmodeled pins.


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Toggling a specic current bias display

To turn on the display of a specic current bias point:

1. In Capture, from the Edit menu, choose Select All.

2. Click the Toggle Selected Bias Current button in the Bias Point toolbar ( ). This willeither turn off all current bias values for every pin on the schematic page, or they will allbe turned on, depending on the previous state. Click the button again, if necessary, toturn everything off. If there is no change in the display either way, be sure that EnableBias Current Display is checked.

3. Click the mouse on an empty area of the schematic page to deselect everything.

4. Click the specic pin you want to display the current on, in order to select it.

5. Click the Toggle Selected Bias Current button in the Bias Point toolbar ( ).

You should now see only the current bias point value for the specic pin you are interested in.All other current bias points on the schematic page should be turned off.

Toggling a specic voltage bias display

To turn on the display of a specic voltage bias point:

1. In Capture, from the Edit menu, choose Select All.

2. Click the Toggle Selected Bias Voltage button in the Bias Point toolbar ( )

This will either turn off all voltage bias values for every net on the schematic page, or theywill all be turned on, depending on the previous state. Click the button again, ifnecessary, to turn everything off. If there is no change in the display either way, be surethat Enable Bias Voltage Display is checked.

3. Click the mouse on an empty area of the schematic page to deselect everything.

4. Click the specic net you want to display the voltage on, in order to select it.

5. Click the Toggle Selected Bias Voltage button in the Bias Point toolbar ( ).

You should now see only the voltage bias point value for the specic pin you are interestedin. All other voltage bias points on the schematic page should be turned off.


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Differences between bias point display in Capture vs.PSpice Schematics

Bias point display in OrCAD Capture works very much the same way as in MicroSimSchematics Release 8. There are, however, a few differences that should be noted.

1. The "stale" condition that was supported in Schematics is not supported in Capture. Thebias point values you see will always reect the calculations from the last simulation run.

2. In Schematics, for a current bias point, the leader line on the bias point label indicatedthe direction of the current ow. Current direction is not indicated in Capture.

3. In Schematics, two symbols were provided (VIEWPOINT & IPROBE) that were formerlyused for bias point display. These symbols became redundant in Release 8 with theimproved bias point display feature. These symbols are not available with Capture.


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Index

Bbias point display 7bias point menu 9

CCapture vs. PSpice Schematics with bias

point display 17controlling the display of bias points 11current bias points 16

Ddisplaying bias point values 8

Mmenu commands for bias point display 14moving bias points 13

PPSpice Schematics vs. Capture with bias

point display 17

Ttoggling a specific current bias display 16toggling a specific voltage bias display 16toolbar controls for bias point display 15

Uupdating bias point values 13

Vvoltage bias points 16

WWhat is bias point display? 7


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Documents

Bias Point Display