Product Documentation
Virtuoso Parasitic Aware Design User Guide
Product Version IC23.1, November 2023

2

Parasitic Aware Design in ADE Explorer and ADE Assembler

The advanced Virtuoso Parasitic Aware Design (VPAD) functionality is available only in ADE Explorer and ADE Assembler, and can be enabled with the corresponding ADE licenses.

Advanced parasitic aware design functionality, includes the functionality to:

For more information on parasitic aware design features seeAvailability of Parasitic Aware Design Features.

Chapter Contents

This chapter contains the following main topics:

Accessing Parasitic Aware Design Functionality

You can access parasitic aware design functionality using one of the following methods:

Customizing Parasitic Assistant Display

You can customize the look and feel of each of the parasitic assistants in the following manner to best suit your needs:

Parasitic Aware Design Workspace Configurations

The Virtuoso Schematic Editor provides three workspace options in the Window menu:

Parasitics-Estimates: The Parasitics-Estimates workspace is used for the specification of parasitic estimates. This workspace contains the Parasitics & Electrical Setup Assistant.

Parasitics-Filters: The Parasitics-Filters workspace is used to generate refined extracted views. It comprises of the Parasitic Filters Assistant.

Parasitics-Report: The Parasitics-Report workspace is used to report parasitic estimated/extracted values and compare parasitic views. This workspace contains the Parasitic Report Assistant.

You will only be able to access parasitic workspaces when viewing a schematic. When viewing the Welcome to ADE Assembler tab, you will not be able to access parasitic workspaces. Parasitic assistants will however be available through standard menu selection.

The Parasitics-Estimates workspace focuses on estimated parasitics while Parasitics-Filters is used in the extracted parasitics flow. The Parasitics-Report workspace can be used with both the parasitics/LDE (estimated) and extracted flows.

Setting Up and Using Parasitics

This section contains information on:

And, the contents of the Parasitics/LDE menu:

An Introduction to Parasitic Estimates

The parasitic aware design flow provides the functionality to generate estimated parasitics, pre-layout, for simulation. Here, parasitic values are specified through estimates which are stored in parasitic estimate cell views separate from, but still associated with, the schematic view.

R, C, L and K parasitic estimates are supported.

After layout is done, and has been extracted using Quantus QRC/RCX to create an extracted view, parasitic aware design can compare these parasitic estimates against the actual parasitic values, highlighting any parasitics that exceed their estimated values or differ from them by more than any optional specified tolerances. To achieve this you can control the comparison method which can treat estimates as either limits or targets, with a specified tolerance expressed as a percentage.

See Extracted Parasitics for information on how to compare generated estimate views against existing extracted views.

Estimated parasitics, through the performance of a pre-layout simulation, will help ensure that your design will function correctly with specific estimated parasitic values. Once the design has been laid out, the actual extracted parasitic values can then be compared against the estimates.

Some benefits to using parasitic estimates include:

Parasitics/LDE – Setup

You must set up parasitics before starting any additional parasitic tasks. Choose Parasitics/LDE – Setup to display the Parasitics & LDE Setup form, as shown below.

Figure 2-4 Setup Parasitics and LDE Form

The following topics describe the different tabs of the Parasitics & LDE Setup form:

General Tab

Click browse (...) to open the Library Browser window from where you can choose an alternative schematic design for use.

The library, cell, and view name will also be displayed in the Build Parasitic/LDE View form (see Building the Parasitic/LDE View) that you use to build the parasitic/LDE view.

You can set the showAllCellViews environment variable to specify how to populate the library and cellview names on this tab.

This tab contains the following fields:

Form Field Description

Design Under Test

Specifies the Library, Cell, and View names of the top-level schematic design that parasitic estimates should be associated with.
- Library

Specifies the library name.
- Cell

Specifies the cell name.
-View

Specifies the view name.

Power and Ground Nets

Specifies the power and ground nets. Parasitic aware design uses these nets to determine which parasitic capacitances are decoupled (one side of the capacitor is connected to a power or ground net) or coupled (the capacitance is between two other nets).

If this field is left blank, all capacitances will be coupled.

See also Capacitance Estimates.

You can either enter the net names or select the power and ground nets directly from the schematic. To select the nets from schematic, click Select from Schematic. The schematic view is displayed in a new tab if it is not already open. If the schematic is already open in another tab, that tab will be displayed. Now you can select the supply nets on this tab. After selecting the supply nets, press the Esc key. The Setup Parasitics and LDE form will be displayed again and the names of the selected nets are shown in the field.

Device M-Factor Parameter Names

While generating a netlist with parasitics, if the tool finds any cell with parameter names listed in field, it expands the cell if the Expand Devices with M-Factor check box is selected. However, when using LDE parameters, cells will be expanded according to the multiple factors used in the layout or MODGEN constraint. In both cases, the m-factor value on the individual expanded devices in the netlist is reset to 1.

Device Finger Parameter Names

While generating a netlist with parasitics, if the tool finds any cell with the given finger parameter names, it expands the cell if the Expand Devices with M-Factor check box is selected. However, when using LDE parameters, cells will be expanded according to the multiple fingers used in the layout or MODGEN constraint.

Important Points to Note

Schematic Estimates Tab

This tab sets the name of the schematic view and the default resistance and capacitance values that are to be used when estimate constraints are first created. These values can be constants or expressions that contain ADE variables.

Expression syntax must conform to the standards laid out in the Analog Expression Language Reference.

The tab contains the following fields:

Form Field Description

Netlist View Name

Specifies the name of the view to be used to create a netlist that includes schematic parasitic estimates.

R

Sets the default parasitic estimate value for resistance.

L

Sets the default parasitic estimate value for inductance.

K

Sets the default parasitic estimate value for mutual inductance.

Coupled C

Sets the default parasitic estimate value for coupled capacitance.

Decoupled C

Sets the default parasitic estimate value for decoupled capacitance.
Use this tab when you want to include schematic parasitics in the simulation netlist.

You can specify the initial values of the fields described above by setting the corresponding variables in the .cdsenv file as shown in the following examples:

msps.estimates defaultR string “1.0”
msps.estimates defaultL string “1.0p”
msps.estimates defaultK string “0.1”
msps.estimates defaultCC string “10f”
msps.estimates defaultDC string “10f”

Setting Up Parasitics Summary

To setup parasitics:

  1. Select Parasitics/LDE – Setup to display the Parasitics & LDE Setup form.
  2. Complete the Design Under test section on the General tab as required.
  3. Enter the names of the power and ground nets in the Power and Ground Nets field.
    You can enter the net names manually or click the Select From Schematic option. Then, select the nets directly from the cellview.
  4. On the Schematic Estimates tab, set the Default Estimate Values for R, L, K, CoupledC, and DecoupledC.
  5. Click OK to complete parasitic setup and close the Parasitics & LDE Setup form.
    Parasitic functionality will now be available in all tabs open in the current session window.

Layout Tab

This tab specifies the options to include parasitics from a layout view, or to include layout dependent effects (LDEs) from Modgen constraints or from a layout view (partial or complete).

For more information about simulating designs with LDE, see the Simulating Designs with LDE section in Virtuoso ADE Assembler User Guide. For information on the electrically aware design flow, see Virtuoso EAD Flow user guide.

This tab contains the following fields:

Form Field Description

Netlist View Name

Specifies the name of the view to be used to create a netlist that includes parasitics or LDE parameters from the layout view.

Both LDE parameters and layout parasitics can be added to the same netlist view.

Layout Lib Name for Parasitics & LDE

Name of the library of the design that contains a layout cellview with layout parasitics.

Layout Cell Name for Parasitics & LDE

Name of the design cell that contains a layout view with layout parasitics.

Layout View Name for Parasitics & LDE

Name of the layout view that contains layout parasitics to be used in resimulation of a design. This can be a partial or a complete layout view.

When you specify a layout name in this field, select Include Parasitics From Layout option in the Parasitics section on the Layout tab or the Layout View option in the LDE section on the Layout tab. This is helpful in the EAD or LDE flow.

You can choose to include both the LDE parameters and the layout parasitics from the same layout view.

Parasitics

This section contains fields to be used while including parasitics from a layout view. This is required while simulating a design with layout dependent effects or in the Electrically Aware Design flow. For more details, refer to Virtuoso Electrically Aware Design user guide.

- Include parasitics from

Specifies the source of parasitics. You can select any one of the following three sources:

  • None - No parasitics are used. This is the default option.
  • Schematic Estimates - Includes estimates from the Parasitics & Electrical assistant. These are the same estimates used in the Schematic Estimates mode. This option allows the use of LDE with estimated parasitics
  • Layout - Includes parasitic estimates from the layout view specified in the Layout View Name for Parasitics & LDE field.
When you choose to include layout parasitics in simulation, you also need to change the parasitic mode to Layout (Parasitics/LDE).

- Extraction Corner for Layout Parasitics

When you choose to include parasitics from the specified layout view, names of the all the extracted corners for that layout are listed in this field. Select name of the desired corner.

- Reference Net for Grounded C

Specifies name of the ground net to be used for grounded capacitance. You can either type a name in this field or click Select from Schematic to select a net from the design schematic.

Important Notes

  • A reference net for grounded C is not required if you are extracting only R estimates or if you are stitching only R estimates from RC extraction.
  • You can specify name of a global net that does not exist in the design under test. The net will be created in the netlist view as an inherited connection so that you can use a netSet property on the cell instance to specify the net to identify it with. The netSet property name is the same as the net name.
  • You can use he msps.layout referenceNet environment variable to set the initial default value of the reference net field. However, after you specify a value for this in the LDE and Parasitics Setup form, the value for reference net field is saved in the design setup and the referenceNet environment variable is not considered for the design. This allows different designs to use different reference nets without interference.

- Expand Devices with M-Factor

Specifies if it is required to expand the devices with multiple factors before generating a netlist.

When this option is selected, the m-factor parameter on the schematic device is then used to create multiple parallel devices in the netlist view. This allows the parasitics for the nets between each m-factor instance in the layout to be brought into the netlist view for simulation. If this check box is disabled, the device is represented as a single instance in the netlist view, and the parasitics between m-factor instances will not be included.

LDE

This section contains fields to be used while including layout dependent effects from a layout view. This is required while re-simulating a design in the Layout Dependent Effects flow.

When you choose to include LDE parameters in simulation, you also need to change the parasitic mode to Layout (Parasitics/LDE).

- Include LDE From

Specifies the source of LDEs. You can choose any one of the following options:

  • None - This is the default option, which specifies that no parameters from layout or MODGEN constraints are to be used.
  • MODGEN Constraints - Includes LDEs extracted from the Modgen constraints defined for the given constraint cellview.
  • Layout View - Includes estimates from the layout view specified in the Layout View Name for Parasitics & LDE field.
    If you include parasitics from layout in the Parasitics section, you cannot choose to use LDEs defined in MODGEN constraints. This is because parasitics and LDE parameters must come from the same source.

Ignore Dummies Back-Annotated to Schematic

Specifies that if there are any dummy cells backannotated from layout to the schematic view, they need to be ignored while generating a netlist for simulation.

For more details on backannotated dummy instances, refer to Dummy Instances Backannotation.
When simulating designs with LDEs, Virtuoso runs PVS-LVS to read the Modgen constraints and to extract the values of LDE parameters. The Virtuoso IPVS log file is saved in the /tmp/<username>_pvs_* directory and is automatically deleted when you exit the Virtuoso session. However, for debugging purposes, you can preserve the Virtuoso IPVS log file. For this, set the Virtuoso_IPVS_log environment variable before starting Virtuoso. For more details, refer to Debugging Problems in Virtuoso IPVS in the Virtuoso IPVS User Guide.

Extracted Tab

This section specifies name of the extracted view that contains the extracted parasitic details.

See also: Creating an Analog Extracted View.

Parasitics/LDE – Create Estimates

Selecting Parasitics/LDE – Create Estimates displays the Parasitics & Electrical Setup Assistant.

Amongst other features, from here you can create estimated parasitics and build a parasitic/LDE view.

When this option is selected, the schematic specified in the setup form will be opened automatically in a new tab or raised if it is already open.

Parasitics/LDE – Create Filters

Selecting Parasitics/LDE – Create Filters displays the Parasitic Filters Assistant.

Amongst other features, from here you can create parasitic filters and refine the extracted view.

When this option is selected, the schematic specified in the setup form will be opened automatically in a new tab or raised if it is already open.

Parasitics/LDE – Report

Selecting Parasitics/LDE – Report displays the Parasitic Report Assistant.

Amongst other features, from here you can create a range of parasitic reports (including comparing the parasitic/LDE and extracted views), export this report information, and cross-probe with the extracted view.

When this option is selected, the schematic specified in the setup form will be opened automatically in a new tab or raised if it is already open.

Parasitics/LDE – Compare

Selecting Parasitics/LDE – Compare displays the Compare Parasitics form (see Parasitic Comparisons and Comparison Reports).

From here you can setup parasitic comparisons for the parasitic/LDE schematic and extracted views.

Parasitics/LDE – Options

Selecting Parasitics/LDE – Options displays the Options form.

The Options form contains a selection of options related to backannotation and parasitic probing for estimated and extracted parasitics (see Extracted Parasitics).

Values entered here will determine some of the content of other parasitic aware design forms.

Figure 2-5 The Options Form

GUI Item Description

Backannotation in Schematic

- Backannotate values

Specify the backannotation values that you want to view (R, C and/or L).
- Font Size

Specify the label font size for displaying parasitic backannotation.
- X Offset

Sets the horizontal offset from the centre of the net when displaying parasitics.
- Y Offset

Sets the vertical offset from the centre of the net when displaying parasitics.

Parasitics Probing Reports

(See also the Extracted Parasitics).
- Initially Sort By

Specify the initial sorting method (Instance, Type, Value, From, or To) to be used when probing parasitics on nets
- Extracted Nets

Check the grouped option to report parasitics for the whole design net when probing an extracted net (this will work as if probing in the schematic). For detailed debugging however, you should clear the grouped option. In this case the report will be specific to the selected extracted net fragment.

The effective R results will be shown if you have setup effective R using the Setup ~R Reporting option in the Parasitic Report assistant.

Component Display in Extracted View

(See also the Extracted Parasitics).
- Net names on parasitic instance terminals

Enables the display of the names of nets connected to terminals of parasitic instances in the extracted view.

Extracted Parasitics

This section on extracted parasitics contains the following information:

Related Information

An Introduction to Extracted Parasitics

Parasitic aware design also provides functionality that enables you to filter parasitics from an extracted view to create a new, refined, extracted view so that you can debug the sensitivities of various nets to parasitics and speed up simulation.

See also the Parasitic Filters Assistant.

To achieve this, parasitic aware design uses the Virtuoso unified constraints system (see Virtuoso Unified Custom Constraints User Guide) to create and edit filters (special parasitic aware design constraints).

The refined extracted parasitics options can be accessed via the Parasitics/LDE - Create Filters menu option or the Parasitics - Extracted workspace.

An Introduction to Parasitic Filters

You can make selections from the schematic view to populate a filter.

These filters are stored in the constraints database, along with other constraints, but are only retrievable using parasitic aware design. Parasitic aware design will use these filters to determine which parasitics should be maintained in any resultant refined extracted view.

The Parasitic Filters Assistant can be used to filter parasitics from the entire extracted view using a threshold value, or you can refine parasitics on a net by net or block by block basis, to simulate the new extracted view.

Extracted Parasitics Flow Overview

A brief overview of the extracted parasitics flow, in the back end, is described as follows:

Optimizing an Extracted or Layout View

You can sweep the parameters of an extracted design, run simulations, and optimize the design to meet the desired specifications. The simulation results are reported in the Results tab and the optimized parameter values can be backannotated to the schematic.

To simulate an extracted or parasitic/LDE view, do the following:

  1. Click Parasitic/LDE – Setup.
    The Setup Parasitics and LDE form is displayed.
  2. Specify the name of the extracted view in the Extracted View Name field.
  3. Click OK to close the Setup Parasitics and LDE form.
  4. In the Parasitic Mode toolbar, select Extracted (Parasitic/LDE).
    If you are considering the layout-dependent effects (LDEs) or parasitics from a layout view, which is specified in the Layout view name for parasitics and LDEs field in the Setup Parasitics and LDE form, select the Layout (Parasitics/LDE) parasitic mode.
    Note the following in the Data View pane:
    • The device parameters that define the m-factors or fingers are disabled and shown with a strikethrough, as shown in the following figure.
      In the above example figure, M1/fingers and M0/fingers are the two parameters that are defining the number of fingers for devices M1 and M0, respectively. This indicates that the extracted view simulation flow will not consider these parameters because they have already been extracted out and are fixed in the extracted view. That is, the flow will not optimize the device multiplier or the number of fingers in a device.
      You can specify the names of parameters that define these properties for a device in the Layout Tab section of the Setup parasitics and LDE form.
      For all other device parameters, such as M1/l or M0/fw in the above figure, which are not fixed in the extracted view, the values will be taken from the instances in the extracted view. The values given in the schematic view will be ignored.
    • You cannot create any new parameter to define the m-factors or fingers for a device.
  5. Ensure that the run mode is set to one of the following modes:
    • Single Run, Sweeps or Corners
    • Monte Carlo Sampling
    • Local Optimization
    • Global Optimization
    • Manual Tuning
      Currently, this feature is not supported for other run modes.
  6. On the Run toolbar, click Run Simulation to run the simulation.
    The simulation is run by using the extracted or the parasitic/LDE view for the testbench. After the simulation is successfully run, observe the following:
    • All the parameters added from the schematic view are mapped to the extracted view. In addition, depending on the multiplier factor, an instance in the schematic is mapped to one or more devices in the extracted view.
      For example, an instance M1 in the schematic may get mapped to the four devices in the extracted view that have been elaborated based on the values for the m-factor and fingers parameters. If a device parameter is M1/fw with values set to 5u:1u:20u, when you switch the parasitic mode to Extracted (Parasitic/LDE), the following four parameters are created:
      M1/fw = 5u:1u:20u
M1_1__rcx/fw = M1/fw@           
M1_2__rcx/fw = M1/fw@
M1_3__rcx/fw = M1/fw@
      On the assumption that each finger will take the same value, independent parameters are created for each finger and the parameters are matched against each other so they take the same value at each simulation point.
      The sweep values for parameters are shown on the parameter headers in the Results tab, as shown below.
    • When you place the pointer on the parameter header, the tooltip shows the names of the expanded devices and the values of their parameters used to run simulation.
    • When optimization is complete, you can backannotate the parameter values of the point that best met the specifications. For this, right-click the parameter header and choose Backannotate. In the Back Annotation Options form that is displayed, make sure that the Only device parameters option is selected and click OK. The corresponding device is highlighted in the schematic and the parameter value is annotated.
    • The expanded parameter details are saved in the history. You can view the parameter values used for a particular history by expanding the Parameters tree on the History tab.
      If you have added, modified, or removed any parameter in the extracted mode, the changes are retained after switching to the No Parasitics mode.

Parasitics & Electrical Setup Assistant

See first Setting Up and Using Parasitics as you must correctly setup parasitic before using the Parasitics & Electrical Setup assistant.

Parasitic estimates comprise of a “star-shaped” model for each net.

See also Parasitic Stitching which allows for an arbitrary topology.

Estimates are stored as constraints and for simulation purposes an (parasitic/LDE) estimated schematic cellview must be generated from the design and user-selected estimates.

The Parasitics & Electrical Setup assistant only displays parasitic estimate constraints.

This section on the Parasitics & Electrical Setup assistant comprises of the following:

Accessing the Parasitics & Electrical Setup Assistant

The Parasitics & Electrical Setup assistant can be accessed using one of the following methods:

The Parasitics & Electrical Setup assistant details the current Parasitic Estimate constraints (this is the only constraint type that is listed) which can be expanded to reveal the current constraint members.

The Parasitics & Electrical Estimates Assistant Toolbar

Figure 2-7 Parasitics & Electrical Setup Assistant Toolbar

The Parasitics & Electrical Setup assistant toolbar provides the following options:

The Parasitics & Electrical Setup Assistant Estimate Editor

Click the Estimate Editor icon in the Parasitics & Electrical Setup Assistant and Filter Editor in the Parasitic Filters Assistant toolbars to display an editing table where you can edit various parameters associated with each parasitic estimate.

Figure 2-8 The Parasitics & Electrical Setup Assistant with the Estimate Editor Selected

For more information on how to edit parameter values, see The Constraint Editor in the Virtuoso Custom Constraints User Guide.

Reverting To Default Values

You can restore default values for fields, for example Sweep, by selecting the Revert to default icon to the right hand-side of the edit field.

Figure 2-9 Revert to Default Icon

The Parasitics & Electrical Setup Assistant Context-Menu

Right-clicking over the Parasitics & Electrical Setup assistant displays a context-menu. From here you can perform a variety of tasks including saving parasitic estimates and controlling object visualization on the design canvas and in the Navigator assistant.

Figure 2-10 Parasitics & Electrical Setup Assistant context-menu

The full contents of the Parasitics & Electrical Setup assistant context menu are listed in the table below.

Context-Sensitive Menu Option Description

Expand All Below

Expands all branches in the Parasitics & Electrical Setup assistant to show all estimate member objects.

Collapse All Below

Collapses all branches in the Parasitics & Electrical Setup assistant to hide all estimate member objects.

Select All Members

Selects all constraint members that belong to the currently selected (expanded) estimate.

Delete

Deletes the selected constraint member.

Create Estimated Capacitance

Creates a capacitance estimate constraint for the selected objects.

For more information see Capacitance Estimates.

Create Estimated Resistance

Creates a resistance estimate constraint for the selected objects.

For more information see Resistance Estimates.

Create Estimated Inductance

Creates an inductance estimate constraint for the selected objects.

For more information see Inductance Estimates.

Created Estimated Mutual Inductance

Creates a mutual inductance estimate constraint for the selected objects.

For more information see Inductance Estimates.

Create Override

Creates an estimate at the current level that overrides one at a lower level.

For more information see Constraint Overrides in the Virtuoso Unified Custom Constraints User Guide.

Match Estimate Parameters

Creates a match between two or more estimates selected in the Parasitic Estimates assistant.

You cannot match a resistance against a capacitance estimate. Matching will only work between resistances, and only between capacitances.

The first selected instance is considered the “master” and the second is given a ‘match(<master>)’ value.

For example, if you select two terminals, X and then Y, then select Match Estimate Parameters, this will mean that in any simulation Y will always have the same value as X. This will be the case even if X has a value determined by a sweep. The parasitic net topology is unaffected.

Note: You can match a coupledC estimate with a decoupledC estimate.

Unmatch Estimate Parameters

Removes a match and reverts the selected parasitics back to their default values.

Option will be enabled if at least one of the estimate selections is currently matched.

Select Inst-Terms

Selects all the terminals for the selected instances to be added to the electrical selection setup.

For more information, see Selecting Signals to Save Currents in the Virtuoso Electrically Aware Design Flow User Guide.

Select Inst-Terms Within

Selects all the terminals of the instances within the currently selected instances.

For more information, see Selecting Signals to Save Currents in the Virtuoso Electrically Aware Design Flow User Guide.

Select Inst-Terms Hierarchically

Selects all the terminals for all the instances in the complete design hierarchy.

For more information, see Selecting Signals to Save Currents in the Virtuoso Electrically Aware Design Flow User Guide.

Options

Displays the Constraint Manager Options form.

For more information see Options.

Creating Parasitic Estimates

See Creating Constraints at Different Design Levels in the Virtuoso Unified Custom Constraints User Guide for further information on creating constraints/estimates.

To create parasitic estimates using the Parasitics & Electrical Setup assistant:

  1. Select the nets that you want to create parasitic estimate constraints for from either the design canvas or the Navigator assistant. Alternatively, you can select instance terminal(s) if you only want to create parasitic estimates for a particular instance’s terminal(s).
    Descend into an instance to create a net estimate at that level.
    If, for a given net, there is a parasitic resistance estimate that only contains some of the instance terminals, you can select the remaining instance terminals, or the net, and continue with estimate creation to include the rest of the instance terminals (see also Resistance Estimates).
  2. Select the Create Estimated Parasitics pull-down from the The Parasitics & Electrical Estimates Assistant Toolbar at the top of the Parasitics & Electrical Setup assistant. This will display the following list of parasitic estimates that can be created:
    • Create Estimated Capacitance (see Capacitance Estimates).
      If you create a capacitance estimate for a power net, “Cd” will be displayed against the estimate in the Parasitic Estimates browser to signify decoupled capacitance. Likewise, a “C” will be displayed for coupled capacitance for signal net estimates.
    • Create Estimated Resistance (Resistance Estimates)
      The resistance estimate will only include instance terminals at the current design level. When you view the Parasitics & Electrical Setup assistant at a different design level, it will only display those resistance and capacitance estimates that were created at that level or below.
    • Create Estimated Inductance (Inductance Estimates)
      “RL” will be displayed in the Parasitic Estimates browser as you cannot have inductance purely on its own.
    • Create Estimated Mutual Inductance (Inductance Estimates)
      See Creating Constraints at Different Design Levels which details that constraints/estimates need to be created on a level-by-level basis.
    • Create Custom Estimated Parasitics (Custom Estimated Parasitics)
    • Create Layout Stitching Estimates for Cell - For more details, refer to Creating Layout Stitching Estimates for a Cell in the Virtuoso Electrically Aware Design user guide.

After you choose which type of parasitic estimate you want to create, it is added to the Parasitic Estimates assistant and a default value is assigned to it. If required, you can change the value of an estimate.

You can now proceed to Building the Parasitic/LDE View.

If you specify the estimate value as an expression using variables, after the parasitic/LDE view is built, the presence of those variables in the Data View pane is checked. If not found, the variables are added to the Global Variables list. You can modify the values of these variables from the GUI.

See also Options for Schematics Estimate Mode.

Capacitance Estimates

See also: Creating Parasitic Estimates.

The method used to Create Estimated Capacitance for nets/buses is dependent upon the number of nets (bus or non-bus) that have been selected in the design canvas or the Navigator assistant.

Only unique net names are displayed in the Create Estimated Capacitance form pull-down.

Using this form, you can create or stitch capacitance between the net you selected and a reference net chosen on this form. The various options displayed on this form are listed below.

– Create/stitch capacitance from this net to <supply-net>: Creates a capacitance between the selected net and a supply net you choose from the drop-down list.

– Stitch all capacitance from this net to any other net in the design: Stitches all the capacitance from the selected net to any other net in the design. For example, if you select netA and select this option, any capacitance available in the layout view to netA is stitched. You do not need to explicitly stitch capacitance between the available net pairs in the design, for example, netA and netB; netA and netC; and netA and gnd!. Every capacitance available in the layout that is connected to netA will be included.

– Stitch coupled capacitance from this net to any other net in the design: Stitches all the coupled capacitance from the selected net to any other net in the design.

– Stitch decoupled capacitance from this net to the reference net: Stitches only the decoupled capacitance from the selected net to the reference net.

The options that are used to stitch a capacitance to other nets in the design are valid only when a layout view is available.

The various options displayed on this form are listed below.

– Create/stitch capacitance from each net to <supply-net>: Creates a capacitance between each selected net and a supply net you choose from the drop-down list.

– Create/stitch capacitance between each pair of selected nets: Creates a capacitance between every possible pair of the selected nets.

– Stitch all capacitance from each net to any other net in the design: Stitches all the capacitance from each selected net to any other net in the design.

– Stitch coupled capacitance from each net to any other net in the design: Stitches all the coupled capacitance from each selected net to any other net in the design.

– Stitch decoupled capacitance from each net to the reference net: Stitches only the decoupled capacitance from each selected net to the reference net. The reference net being either one of the selected nets or a supply net.

The options that are used to stitch a capacitance to other nets in the design are valid only when a layout view is available.

Resistance Estimates

See also: Creating Parasitic Estimates.

The Create Estimated Resistance option creates an estimate constraint for each selected net, instance terminal, or pin.

Selecting a net and choosing Create Estimated Resistance creates a resistor from a common central node for the net to each of its instance terminals and pins. This creates a parasitic network known as a star network.

The parameter r represents the resistance associated with each instance terminal or pin. A common value can be set for all parasitic resistors on a net by selecting the net name in the Parasitics & Electrical Setup assistant assistant and editing the r value in the parameter editing table at the bottom of the assistant. The value can be overridden for individual terminals or pins by selecting the appropriate constraint member and editing its associated r value in the parameter editing table.

It is not always desirable to create a resistance for every instance terminal and pin on a net. Variations of the star network can be made as follows:

The resistance estimate can include the instance terminals and pins at the current design level only.

Inductance Estimates

See also: Creating Parasitic Estimates.

You can use the Parasitics & Electrical Setup Assistant to create both inductance and mutual inductance estimates using the Create Estimated Inductance and Create Estimated Mutual Inductance options, respectively, from the Create Estimated Parasitics pull-down on The Parasitics & Electrical Estimates Assistant Toolbar. Both of these options can have a number of use models, for example:

Creating estimated (self) inductance use models:

  1. You can select a net in the schematic canvas (or using the Navigator assistant) and then select the Create Estimated Inductance option. In this case, the L estimate members will be all the instance terminals of the nets. R estimates will also be created, in series at each instance terminal when L is added (if not already present).
  2. Alternatively, you can select instance terminals in the schematic and then choose the Create Estimated Inductance option. Here, the L estimate members would be the selected instance terminals only. If, for a net, an L estimate already exists, but with only a subset of its instance terminals, it is possible to extend the L estimate for the same net by selecting additional instance terminals on the schematic canvas, or in the Navigator, and then choosing the Create Estimated Inductance option in the browser. All of the newly selected instance terminals would now be added to the existing L estimate. R estimates will also be created, in series at each instance terminal when L is added (if not already present).
    If you select instance terminals for more than one net, multiple L estimates will be created, each corresponding to a specific (unique) net.

Creating estimated mutual inductance use models:

  1. You can select two different inductors (two members from one or more L estimates in the Parasitics & Electrical Setup assistant browser) and then choose the Create Estimated Mutual Inductance (K) option from the Create Estimated Parasitics pull-down. In this case, an estimated K will be created with the chosen inductors (the members of the L estimate) being its members.
  2. You can select more than two inductors (more than two members from one or more L estimates in the Parasitics & Electrical Setup assistant browser) and then choose the Create Estimated Mutual Inductance (K) option.
    When you select more than two inductors, to create a K estimate, a Create Mutual Inductance form is displayed. From here, you can specify what inductor is to be the reference inductor. That is, where mutual inductance will be created between the reference L and all other inductors.
  3. You can select two instance terminals and then click the K option. Here, if any of the selected instances are not existing members of an L estimate, an L estimate will first of all be created, using the selected instance terminals, prior to creating a K estimate for the two instance terminals. R estimates will also be created, in series at each instance terminal when L is added (if not already present).
  4. You can select more than two instance terminals on the schematic canvas, or from the Navigator, and then click the Create Estimated Mutual Inductance (K) option. Here, L estimate will be created for all the instance terminals that are not already members of a L estimate, prior to the creation of multiple K estimates.
    Again, the Create Mutual Inductance form is displayed to allow you to specify the reference inductor. Mutual inductance estimates will then be created between the reference L and the other inductors.
    If you Cancel this form, neither estimated L nor estimated K will be created.
    Figure 2-13 Create Mutual Inductance Form

Custom Estimated Parasitics

See also: Creating Parasitic Estimates.

The Create Custom Estimated Parasitics command on Parasitics & Electrical Setup Assistant allows you to use custom parasitic models in your design. These models are different from the standard R, C, L, or K types of parasitics, which are not always accurate enough to depict the required parasitic model. You can use custom parasitics to specify a custom topology that more closely represents the desired parasitic network on any given net.

The following example shows how a custom topology can be created for a two-terminal net. The parasitic network is created in a new schematic cellview. It defines a resistance network between two pins which represent the terminal connections on the net. Capacitance is connected from various nodes inside the network to a third pin. This pin is used to connect the capacitors to an external reference net when the model is placed.

It is not mandatory to define the implementation of a parasitic cell in the schematic view. Instead, you can define a parasitic cell in any HDL.

You need to associate your parasitic cell with a symbol view that has pins corresponding to the external connections required to be created. The symbol view is used for the following purposes:

A symbol for the example parasitic cell shown above can be created as given below.

Some important requirements for the symbol view of a custom parasitic cell are listed below:

The following topics explain how to create and configure a custom parasitic estimate:

Creating Custom Parasitic Instances

To create a custom parasitic instance, select one of more nets on the schematic and choose the Create Estimated Parasitics – Create Custom Estimated Parasitics command on the Parasitics & Electrical Setup Assistant.

The Create Custom Estimated Parasitic form is displayed. In this form, select the library, cell, and view name of the custom parasitic cell, as shown in the figure below.

Alternatively, you can click the browse ( ) button to browse and select the required cellview.

Click OK to close the form.

An instance of the custom cell is created in your design and is listed in the Parasitics & Electrical Setup assistant, as shown in the figure below.

If a net has a custom parasitic instance specified on it, no other parasitic can be inserted on it.

Configuring Custom Parasitic Instances

Click the parasitic instance in the assistant and open the Estimate Editor to display its properties. Observe that the library, cell and view name of the parasitic cell are displayed in the parLib, parCell, and parView properties of the instance. If required, you can select a different library, cell, and view.

You can now change the values of the properties to configure the instance.

Entering Parasitic Sweeps

You must select the Estimate Editor icon in the Parasitics & Electrical Setup assistant toolbar to display the parameter editing table.

Sweeps are set in the parameter editing table in Parasitics & Electrical Setup Assistant by expanding the l, r, c or k parameters.

Any instance terminal rows, in the Parasitics & Electrical Setup assistant editor section, will be left blank unless the r or l value has been explicitly overridden.

Figure 2-14 Parasitic Sweeps set in the Parasitics & Electrical Setup Assistant

The syntax is identical to that used for sweeps in global variables and parameters in ADE Explorer or ADE Assembler. For example, you can provide a comma-separated list of values: “10, 15, 25” or specify start, step, and stop values: “10:2:20”.

Specifying a range or sweep will create parasitic parameters in the Parasitics tab of the Variables and Parameters assistant (for information about this assistant, see the Virtuoso Analog Design Environment XL User Guide) and allows you to sweep parasitic values during simulation runs. Parasitics can be swept at the same time as, or separately from, device parameters. See The Parasitic Mode Toolbar for running parasitic sweeps.

Figure 2-15 Parasitic Sweep Displayed as Parasitic Parameter in Variables and Parameters Assistant

Note the following:

Restoring Default Sweep Values

You can restore default sweep values by selecting the Revert to default icon to the right hand-side of the edit field.

Figure 2-17 Revert to Default Icon

When estimates are matched their sweeps are also matched. This means that matched estimate components will be swept together during simulation.

Enabling and Disabling Parasitic Sweeps

You can enable/disable parasitic sweeps in the Parasitic Estimates assistant or the Parasitics tab of the Variables and Parameters assistant.

Enabling and Disabling Parasitic Sweeps in the Parasitics & Electrical Setup Assistant

You can enable/disable parasitic sweeps directly in the Parasitic Estimates assistant (without having to use the Parasitics tab of the Variables and Parameters assistant).

To do this, first of all ensure that:

From here, you can now enable/disable the current estimate sweeps by selecting or deselecting Enable/Disable Parasitic Sweep... from the parameter editing table context-menu or the adjacent check box.

Figure 2-18 Check box for Enabling/Disabling Parasitic Sweep

Enabling and Disabling Parasitic Sweeps in the Parasitics Tab of the Variables and Parameters Assistant

You can enable/disable parasitic sweeps in the Parasitics tab of the Variables and Parameters assistant by selecting or deselecting the check box next to each sweep parameter.

Saving Parasitic Estimates Created in the Current Session

Click the Save Estimates icon in the Parasitic Estimates assistant toolbar to save (or update) the parasitic estimates that have been created or edited in the current session.

You can also use the File – Save (Constraint) option on the main menu bar.

For more information on the other options available in the Save Estimates pull-down see Save Constraints in the Virtuoso Unified Custom Constraints User Guide.

Save a Copy will also save parasitic estimate and parasitic filter information.

Figure 2-19 Save Estimates pull-down options in the Parasitic Estimates assistant toolbar

Building the Parasitic/LDE View

Once you have finished Creating Parasitic Estimates you can now proceed to building a parasitic/LDE view.

After creating one or more new parasitic estimates, the Build Parasitic/LDE View icon will indicate, with an exclamation mark, that a new parasitic/LDE view is required to be built to accommodate the new estimates.

Click the Build Parasitic/LDE View icon on the Parasitics & Electrical Setup assistant toolbar to display the Build Parasitic/LDE View form.

Figure 2-20 The Build Parasitic/LDE View Form

To build a parasitic/LDE view:

  1. Specify the View Name for the parasitic/LDE view to be generated.
    The default is estimated but this can be changed, allowing you create multiple parasitic/LDE cellviews.
    Using resistance, capacitance, or inductance values from a layout view to creates estimates checks out additional licenses.
    The Library Name, Cell Name, and View Name option settings are initially automatically infilled from the Design Under Test settings in the Parasitic/LDE Setup form (Setting Up and Using Parasitics). If you change the View Name in the Build Parasitic/LDE View form, this will not however update the setup form nor, consequently, the view that is used when reporting estimates (see the Parasitic Report assistant.
  2. Optionally, set scale factors for each parasitic type by activating the Multiply estimated parasitics by option, and entering scale values for R, L and C.
    Each scale factor value entered will be applied globally to all parasitic estimates of the relevant type. A scale factor of “0” should not be entered.
    Default values for the Build Parasitic/LDE Schematic form can be controlled by the following .cdsenv entries:
    msps.estimates viewName string "estimated" msps.estimates scaleR float 1.0 msps.estimates scaleL float 1.0 msps.estimates scaleC float 1.0
  3. Click the OK button to build the parasitic/LDE view.
  4. Parasitic aware design will now create a flattened view of the schematic hierarchy, inserting the (scaled) estimates. The new parasitic/LDE view will be of a schematic view type. After the parasitic/LDE view is created, the tool displays the following message confirming the creation of the view and listing the parasitics found.
    Figure 2-21 Build Parasitic/LDE View Successfully Created
    Before building the parasitic/LDE view, you can set the reduceParallelCaps environment variable to t to search for parallel capacitors in the parasitic/LDE view and to merge them into a single device.
The parasitic/LDE view is used for netlisting purposes only and does not display a usable schematic if opened.

Simulating and Probing Results

To run simulations using the generated parasitic/LDE view, you must change your configuration or create a new configuration view. Once simulation has completed you can then probe the results. This task can also be performed using the schematic testbench, via a switch view list.

See also The Parasitic Mode Toolbar. This toolbar can be used to bind all tests to the new parasitic/LDE view for simulation.

As the flattened schematic is only used for netlisting you will have to probe using the original schematic. This involves probing out-of-context where parasitic aware design will map between the design and estimated schematics.

Parasitic Stitching

Virtuoso Parasitic Aware Design can be used to create estimates directly based on an existing layout, of a similar design, where an existing Quantus QRC extracted view can have its parasitics stitched into the parasitic/LDE view.

As parasitic stitching involves a pre-layout simulation flow, the extracted view being from an existing, similar design, you must choose a view that models the parasitics with the desired accuracy (the stitching process will not modify parasitics to compensate for differences in m-factored devices, transistor fingers, or device sizes).

You must also provide schematic mapping information between the two designs if they do not match (the equivalent nets and instances).

Parasitic stitching provides for:

For more details, refer to the following topics:

Setting Parasitic Stitching

To set parasitic stitching:

  1. Select the parasitic estimate for the net(s) to be stitched to in the Parasitics & Electrical Setup assistant browser.
  2. Expand the source parameter in the parameter editor and select extracted view or layout view.
    Figure 2-22 Specifying Parasitic Stitching
    Selecting extracted view as the source will add further stitching parameters to the parameter list.
    Figure 2-23 Selecting Extracted View as Source Adds Extra Stitching Parameters

Similarly, if you select layout view as a source for parasitic stitching, four additional parameters, layLib, layCell, layLib, and extCorner appear in the parameters list.

Stitching to a layout view is useful in the EAD flow. For more information, refer to Virtuoso Electrically Aware Design Flow Guide.
  1. If you have chosen to stitch the parasitic to an extracted view, set the ext parameter values as required.
    • extLib: list of available libraries
    • extCell: lists the cells in the selected library
    • extView: lists the available extracted views
      All of the above must point to an Quantus QRC extracted view that exists.
    • extNet: lists all (for L or R only) extracted view net names (converted to schematic namespace). The extNet parameter value must exist in the extracted view.
      Similarly, if you select layout view as a source for parasitic stitching, set the following parameters as required:
    • layLib: name of the library that contains the layout cellview
    • layCell: name of the cell that contains the layout view
    • layLib: name of the layout view
    • extCorner: name of the extracted corner
  2. (for C only) Set the netMap from a list of pairs mapping net members to nets in the extracted view.
    Extracted view stitching parameters for C differ from R and L in that a netMap option is available rather than an extNet option. There is also no terminalMap option for capacitances. Also, the netMap parameter is not available when you stitch an estimate to a layout view.
  3. Set the terminalMap terminal values as required (for L or R only). The instance terminals must exist in both the schematic and extracted views and have complete mapping.
    This parameter field lists pairs mapping the current design’s terminals to the extracted design’s terminals. Both elements of the pair detail the instance and terminal name in the schematic namespace, separated by a colon.
    When stitching R or L parasitics, the entire hierarchical schematic net is replaced from the current schematic down. The terminalMap parameter contains an entry for each instance terminal on all non-hierarchical instances connected to the net at the current design level and below. In addition, any estimates on the same net in lower levels of hierarchy will be ignored. Also, the terminalMap parameter is not available when you stitch an estimate to a layout view.
  4. Set the include parameter value as required.
    Selecting threshold will add a further parasitic type (for example R>) parameter value field.
    Figure 2-24 Include Parameter Value Options
  5. Optionally, set the numeric threshold value where parasitics with values below the threshold will not be stitched into the parasitic/LDE view.
  6. Set the scale parameter value as required.
  1. Optionally, set the numeric threshold value where parasitics with values below the threshold will not be stitched into the parasitic/LDE view.
  2. Set the scale parameter value as required.

The scale value is applied to each parasitic instance stitched by estimate. This scale value works in addition to the Multiply parasitics by fields in the Build Parasitic/LDE View form. For example, if you set the R multiply field in this form to 2, and the scale value in an R stitching estimate to 1.5, the R parasitics stitched by this estimate will be scaled by a factor of 3, which is 2 * 1.5.

For information on setting parasitic stitching using SKILL, see parModelCreateNetL, parModelCreateNetR, and parModelCreateNetC.

Including Instances that are Ignored in Stitched View

During netlisting, some instances are ignored and do not appear in the stitched view because the lvsIgnore property may be set to true for these instances. You can stitch these instances by setting the ignoreLVSInstForStitching environment variable to t and thereby, ignoring the lvsIgnore property. Set the ignoreLVSInstForStitching environment variable to nil to ignore the instances that have the lvsIgnore property set for them.

Ignoring Instances that are Included in Stitched View

During netlisting, some instances that have the lxRemoveDevice property set to true are ignored and do not appear in the stitched view. You can stitch these instances by setting the lxRemoveDeviceForStitching environment variable to nil and thereby, ignoring the lxRemoveDevice property. Set the lxRemoveDeviceForStitching environment variable to t to ignore the instances that have the lxRemoveDevice property set for them.

Important Points to Consider for Parasitic Stitching of Mutual Inductance

When stitching L estimates, the following points must be considered:

Important Points to Consider for Parasitic Stitching of Resistance

When stitching R estimates, the following points must be considered:

Parasitic Filters Assistant

Parasitic filters allow you to select the nets for which parasitics should be included in the refined extracted view (see Refining the Extracted View).

The use of parasitic filters replaces the sbaLib component method of identifying which parasitics to include in the refined extracted view, and provides greater flexibility and control in this area, for example:

This section on the parasitic filters assistant comprises of the following:

Accessing the Parasitic Filters Assistant

The Parasitic Filters assistant can be accessed using one of the following methods:

For more information on accessing assistant panes see Accessing Parasitic Aware Design Functionality.

Figure 2-25 Parasitic Filters Assistant

Enabling Parasitic Filters

To enable the Parasitic Filters assistant (that is, to be in a position to start creating parasitic filters) you must setup parasitics (see Setting Up and Using Parasitics). You may then need to descend into the schematic specified in the setup form.

You can cross-select between the schematic view, the Navigator, and the Parasitic Filters assistant so that when an object is selected, the Parasitic Filters assistant will highlight any filters that are associated with that object.

The Parasitic Filters Assistant Toolbar

The Parasitic Filters assistant toolbar provides the following options:

The Parasitic Filters Assistant Context-Menu

Right-clicking over the Parasitic Filters assistant displays a context-menu. From here you can perform a variety of tasks including saving filters and controlling object visualization on the design canvas and in the Navigator.

Figure 2-26 Parasitic Filters Assistant Context-Menu

The full contents of the Parasitic Filters assistant context menu are listed in the table below.

Context-Sensitive Menu Option Description

Expand All Below

Expands all branches in the assistant to show all filter member objects.

Collapse All Below

Collapses all branches in the assistant to hide all filter member objects.

Select All Members

Selects all parasitic filter members that belong to the currently selected (expanded) filter.

Create Filter

Provides sub-menu options to create net filters for parasitic Capacitance, Resistance, and Inductance. See Creating Parasitic Filters.

Create Cell Filter

Provides sub-menu options to create cell net filters for parasitic Capacitance, Resistance, and Inductance. See Creating Parasitic Filters.

Create Override

See Constraint Overrides in the Virtuoso Unified Custom Constraints User Guide.

Options

Displays the Constraint Manager Options form.

For more information see Options in the Virtuoso Unified Custom Constraints User Guide.

Saving Parasitic Filters Created in the Current Session

Click the Save Filters icon to save (or update) the parasitic filters that have been created or edited in the current session.

You can also use the File – Save (Constraint) option on the main menu bar.

For more information on the other options available in the Save Filters pull-down see Save Constraints in the Virtuoso Unified Custom Constraints User Guide.

Save a Copy will also save parasitic estimate and parasitic filter information.

Figure 2-27 Save Filters pull-down options in the Parasitic Filters assistant toolbar

Creating Parasitic Filters

The following filter creation options are available on the The Parasitic Filters Assistant Toolbar (initially prior to filter creation) and in the The Parasitic Filters Assistant Context-Menu:

Figure 2-28 Creating Filter options available from the Parasitic Filters assistant toolbar

To create a parasitic filter (overview):

  1. Select the design objects in the Navigator or design canvas that you want to create a parasitic filter/cell filter for.
  2. Select the type of parasitic filter/cell filter that you want to create from the The Parasitic Filters Assistant Toolbar or The Parasitic Filters Assistant Context-Menu.
    The parasitic filter/cell filter will be displayed in the constraint table in the Parasitic Filters assistant.
    For more information on parasitic constraints see parasitic filter and parasitic estimate in the Virtuoso Unified Custom Constraints Configuration Guide.

Creating a Capacitance Filter for a Single Net

When a Capacitance (C) filter is created it will have an additional (to the other parasitic filter types) subtype parameter that indicates whether the filter applies to coupled capacitance, decoupled capacitance, or both.

If you set the subtype parameter to coupled or decoupled then you can create a second C filter on the same design object to filter the other subtype.

If subtype is set to both, only one C filter can exist for a particular design object and this will apply to both decoupled and decoupled C.

Figure 2-29 Capacitance filter Subtype parameter pull-down

The subtype parameter does not exist for resistance or inductance filtering.

Creating a Capacitance Filter for Two Nets

If you attempt to create a capacitance filter when two nets are selected the following version of the Create Parasitic Capacitance filter form will be displayed:

Figure 2-30 Create Parasitic Capacitance Filter form with two nets selected for filter creation

Creating Multiple Filters

You can select multiple objects then apply parasitic filters to them using the Parasitic Filters Assistant.

Creating Multiple Capacitance Filters

For capacitance (C) the filter creation process differs depending on whether two nets have been selected or whether more than two nets have been selected.

For information on creating capacitance filters for two selected nets see Creating a Capacitance Filter for Two Nets.

When three or more nets are selected the following version of the Create Parasitic Capacitance filter form will be displayed when you choose Create Filter option:

Figure 2-32 Creating parasitic capacitance filter for three or more nets

Creating Multiple Resistance and Inductance Filter

When applying multiple resistance (R) or inductance (L) filters you should firstly select the multiple objects then select the Create Filter option to create one filter for each selected object.

Editing Parasitic Filters Parameter Values

You can edit one or more filter parameter values using the Parasitic Filters assistant.

The ability to editing multiple values also applies to parasitic estimates.

Figure 2-33 Parasitic Filter assistant’s parameter editing table

To edit parasitic filter threshold values:

  1. Select one or more filters from the upper section of the Parasitic Filters assistant.
  2. Edit single or multiple parameter values in the lower section of the Parasitic Filters assistant
    If multiple filters are selected, common parameter values can be set simultaneously in the same manner as using the Property Editor assistant. They can be set as a group by editing the value in the same row as the parameter name, or individually by expanding the parameter name row to display the values for each filter.

Deleting Parasitic Filters

To delete a parasitic filter:

  1. Select the filter to be deleted in the upper section of the Parasitic Filter assistant.
  2. Click the Delete option on the The Parasitic Filters Assistant Toolbar or in the The Parasitic Filters Assistant Context-Menu.
There is no filter for K as K will be included for any L pairs included in the refine extracted view.

Refining the Extracted View

Click the Refine Extracted View icon in the Parasitic Filters assistant toolbar to display the Refine Extracted View form.

Figure 2-34 The Refine Extracted View Form

Parasitic filters control the content of the refined view.

The purpose of Refine Extracted View is to generate an extracted view that can be used for circuit simulation. The refined extracted view generated is based on the full extracted view created in Quantus QRC or RCX.

The default full extracted view is av_extracted, while the default parasitic aware design refined extracted view name is av_analog_extracted.

After the refine extracted view has been created, a window is displayed summarizing the parasitics in the new view. This information is also displayed in the CIW.

The refined extracted view will not remove any resistance that is associated with inductors as long as the inductors are not filtered out. This will prevent the creation of zero-resistance loops in the refined parasitic net.

GUI Item Description

View Name

Specifies the name of the refined extracted view to be created.

Multiply resulting parasitics by:

Allows you to simulate with different parasitic values. For example, the minimum and maximum expected parasitic values (based on the same extracted view).
R

Set the multiplication factor for resistance parasitics.
C

Set the multiplication factor for capacitance parasitics.
L

Set the multiplication factor for inductance parasitics.

Parasitic Report Assistant

The Parasitic Report assistant can be used to readily view and compare parasitic reports for estimated, extracted, layout, and Smart Views.

It can be accessed in ADE Explorer and ADE Assembler by selecting one of the following options:

The Parasitic Report assistant replaces the Parasitic Report forms that are still available in the parasitics.

The Parasitic Report assistant comprises of the following sections:

When the Compare report tab is selected in the Parasitic Report assistant, the Showing and From report title fields will be replaced by Limit/Target and Actual fields.

Parasitic Report Assistant Available Reports

The following reports can be accessed from the Parasitic Report assistant for estimated and extracted parasitics:

Figure 2-38 Reports Available in the Parasitic Report Assistant

The Probe Design Inst/Net report is available only when the Extracted tab is selected.

Parasitic report results may be grouped into collapsible categories (for example, R, C, L, K) by selecting the View By option in the context menu.

Each report table column is sortable, within a category, by column heading. Sorting criteria can be specified using the Initially Sorted By option in the Parasitic Probing Reports section of the Parasitic Options form (see Parasitics/LDE – Options).

Understanding Parasitic Report Results

The Parasitic Report assistant provides a detailed report of the parasitics in the design. The following table describes how to understand the results displayed in the assistant pane.

Report Type

Name

Description

Net,
Net to Net,
All Nets

R

Displays parasitic resistance elements.

decoupled C

Displays capacitors that are bound to power or ground nets.

coupled C

Displays capacitors between ordinary nets.

self C

Displays coupled capacitors between segments of the same net.

L

Displays parasitic inductances.

K

Displays the mutual inductance (K) ratio.

Example: For two given circuits A and B, the mutual inductance is the ratio of the flux through circuit A caused by the current in circuit B.

Terminal to Terminal,
Probe Design Inst/Net

Reports parasitics between two instance terminals or between a terminal and a pin on the same net.

The terminal to terminal probing does not report parasitics between two pins. It lists the parasitics on all paths between the two terminals.

Net Capacitors

Generates the capacitors for the net report which displays summed capacitances (Sum C) between the selected net and all those nets to which it is connected through parasitic capacitors.

Sum Totals

The Sum totals at the bottom of a report display the effective and summed values. The C, L, and K values are always summed, whereas the R value depends on the type of probing selected for each parasitic type that has been found for the the specified probing type.

  • Terminal to Terminal probing: The R total value displayed is calculated by reducing the parasitic R network between the two terminals.
  • Net probing: Effective R value is a measure of the power lost through the parasitic resistor network (or equivalently, the delta between the power entering the network and the power leaving the network, normalized by the total current entering (or leaving) the network.
    Combining V=IR with P=VI, it is calculated as
    Effective R (R~) = P / I^2
    where:
    P is the sum of the power through the parasitic resistors in the network.
    I is the current entering (or leaving) the network.

The power and current values are read from the DCOP results. Therefore, it is expected to run a single point DC simulation.

Net Reports

For net probing, the report will initially report on the most recently selected net. If multiple nets are currently selected only the most recently selected net will be reported on. Other object types will be ignored.

Net to Net Reports

You can select the nets you want to report on prior to or after selecting the Net to Net report option.

For net to net reporting, the report will initially report on the two most recently selected nets. If more than two nets are selected, all nets other than the last two selected will be ignored. Other object selections will also be ignored.

You can also specify how to identify power and ground nets using the Power and Ground Nets for Decoupled Capacitance Reporting section in Parasitics/LDE – Setup.

Terminal to Terminal Reports

Using the terminal to terminal probing, you can report parasitics between two instance terminals or between a terminal and a pin on the same net.

The Parasitic Report assistant will report parasitics between the two most recent selections only. If multiple selections are done, all terminals or pins other than the last two selected will be ignored. Other object type selections are also ignored.

The terminal to terminal probing does not report parasitics between two pins.
Terminal to terminal report values can differ from whole net report values

When you perform a terminal-to-terminal probe (also known as point-to-point probing) or generate a parasitic report, if two selected terminals map completely to the same extracted nets, a warning describing the situation is displayed. The resultant report will also reveal that no parasitics have been found between these terminals. This happens because the terminals are considered to be shorted, and parasitics will therefore have no influence on the interaction between the two terminals in question.

However, if you subsequently perform a whole net probe on the same net, parasitics could still be reported even if the net is a two terminal only net.

For example, if you consider two m-factored transistors (mFactor = 2) T1 and T2, with the source of T1 connected to the drain of T2. Selecting T1-source and T2-drain, in the schematic, will identify that T1_m1-source is shorted with T2_m1-drain and T1_m2-source shorted with T2_m2-drain. As mentioned, terminal to terminal probing would complete, reporting no parasitics, however whole net probing will identify and report any parasitics that might exist between T1_m1-source and T2_m2-drain.

Selecting Leaf Terminals

The Select leaf terminals form is displayed when you perform terminal to terminal probing and select hierarchical terminals that have more than one leaf terminal.

If both terminals selected have multiple leaf terminals, the Select leaf terminals form will be displayed twice, once for each terminal.

From the Select leaf terminals form you must select the terminals (for example, gate and drain) that you want to measure resistance values for.

The ability to select individual terminals prevents the results of point to point probing of a net, that has parallel resistors, being reported as a sum of the resistance values.

Net Capacitors Reports

Reporting on net capacitors generates a report which displays summed capacitances (Sum C) between the selected net and all the nets that it is connected to via parasitic capacitors.

No report will be generated for “0” capacitances, and no distinction is made between power/ground, and other nets.

All Nets Reports

The All Nets report lists each net in the design along with the total value for the net based on the effective value for R, the summed value for C and L, and the weighted sum for K.

If you are viewing the Estimate or Extracted tabs for All Nets reports, you can right-click over the column headers and choose what type of parasitics (R, L, K, decoupled C, coupled C, and/or self C) that you want to Show.

Probe Design Inst/Net Reports

You should ensure that both the schematic and extracted views are open to facilitate viewing and probing.

Select Probe Design Inst/Net from the report pull-down in the Parasitic Report assistant to display the Extracted Insts report form from where you can:

When probing from the extracted view, highlighting in the schematic view will only work when the schematic is open in its own right. It will not work when the schematic is open through a configuration.

If you attempt to probe from hierarchical blocks/instances, a warning message will be displayed in the CIW. To resolve this you must descend the hierarchy (Edit – Hierarchy – Descend Edit) and probe at the leaf level.

If you are probing a schematic net that exits the current hierarchy level, the probe will be restricted to the instances attached to that net in the current level and not the full design. Probing therefore remains localized.

After you have selected a regular device (instance or net) to probe the relevant Extracted/Schematic insts associated... form is displayed.

This tabular form lists all of the Extracted/Schematic inst names, and their associated Type, that are related to the device that you selected. The results are viewed in sortable columns.

For a design net, the displayed list contains all of the extracted or schematic instances that are attached to that net in the other view type.

If you select one or more extracted instances from the list (using the Ctrl/Shift keys) this causes the extracted view to automatically zoom into those instances, highlighting the selected items in both the schematic and extracted views.

Highlighting of instances only applies to an extracted view, not a layout view.

Clicking on the Save button in the Extracted insts... form displays the Save Instance Report form. For information on saving reports in parasitic aware design see Exporting Parasitic Reports.

There is no corresponding zoom facility on the schematic view.

When you are performing an m-factor selection it is observed that the instances are found, and highlighted, in the same area of the chip. A m-factored device is where a single cell instance represents multiple instances of a parallel connected cell.

Exporting Parasitic Reports

Selecting the Export Parasitic Report button on the Parasitic Report assistant toolbar invokes the Save Parasitic Report form.

Figure 2-40 The Save Parasitic Report Form

From the Save Parasitic Report form, you can Save (then export) parasitic reports in .txt or .csv (comma-separated values) format.

Setting Up Effective R Reports

Selecting the ~R (effective R) option on the Parasitic Report assistant toolbar will display the Setup ~R Reporting form where you can specify your ~R Reporting.

See also Effective R Calculations and Preparing for Resistance Backannotation (Running a DC Analysis).

There are two option tabs, Estimated and Extracted, at the top of the form where you can choose what view type effective R information that you want to setup.

Figure 2-41 Setup ~R Reporting Form

To enable the ~R Simulation Data table, the Enabled option must be checked.

If you have enabled resistance reporting, you must select valid simulation results from the tree displayed. The tree will display results from the simulation history.

Disable this option if DC simulation results are not available or you are yet to build the parasitic/LDE view. To ensure that DC simulation results are available, select the Save DC Operating Point check box on the Choosing Analysis form.

History items are filtered to only display those results that contain a simulation where the current instances have been bound to the chosen cellview. This means that if multiple instances of the DUT (design under test) exist, only those results for the one that you have descended into will be displayed. This is because results for other instances of the DUT will not be valid in this context.

However, if you open the DUT directly, you will see results for all instances of the DUT in all tests. In this scenario, you must choose the appropriate instance path.

Opening an Extracted View from the Parasitic Report Assistant and Cross-Probing Parasitics

Selecting the Open Extracted View option on the Parasitic Report assistant opens (raises) the extracted view or Smart View in a new tab in your current session window. The current report content is unaffected when the new view is opened.

This option is only enabled when the Extracted tab is currently selected in the Parasitic Report assistant.

With the new view raised, you can cross-probe to thisview by selecting the parasitic values in the displayed report. Cross-probing operates by selecting single or multiple items in the report. VPAD zooms and pans to the corresponding instances in the opened view.

Cross-probing from the Parasitic Report assistant is supported for the net, net to net, terminal to terminal, and design/net inst probe reports.

Selections on the view canvas initiate probing in the view. You can switch back to the schematic view tab, and reselect the object you want to cross-probe.

Consider that Extracted View Name on the Extracted tab of the Parasitics/LDE Setup form is set to a Smart View.

To cross-probe this view:

  1. Choose Parasitics/LDE – Report.
    The schematic and the Parasitic Report assistant opens.
  2. Do one of the following:
    • Open the Navigator assistant and select a net.
    • Select a net from the schematic.

    The Extracted tab in the Parasitic Report assistant is populated with the parasitics on the selected net.
  3. Click the Open Extracted View icon from the toolbar of the Parasitic Report assistant.
    The Smart View appears.
  4. Select a parasitic resistor or capacitor from the report on the Extracted tab.

The canvas zooms in to display the selected parasitic as shown in the following figure:

Showing and Hiding Parasitics from the Parasitic Report Assistant

Selecting the Show/Hide button option on the Parasitic Report assistant toolbar will control the display of parasitic values on the design canvas.

The parasitic values displayed on the canvas will be dependent upon which tab is currently raised in the Parasitic Report assistant. If the Estimated tab is current, only parasitic/LDE view parasitics will be annotated on the canvas. Similarly, for the Extracted tab, should that be current. Annotations will also only remain visible when the Parasitic Report assistant is raised.

No parasitic values are displayed if the Compare tab is on view.

Figure 2-42 Annotations on Nets in a Schematic

Comparison Reports

The Parasitic Report assistant can also be used to compare estimated and extracted parasitic views as well as being able to compare two extracted views and two parasitic/LDE views.

To populate this report, select Parasitics/LDE – Compare and complete the Compare Parasitics form (see Parasitics/LDE – Compare and Parasitic Comparisons).

The Compare tab report shows summaries for each net, grouped at the top-level by type. You can choose to see those nets that met (Pass) or exceeded (Fail) the set estimates, and also what parasitic values (R, decoupled C, coupled C, self C) that you want to display in the table.

If you select a net, in the report table, the Estimated and Extracted tabs will show details of that net.

Figure 2-43 The Compare Tab in the Parasitic Report Assistant

The following table describes the status information being relayed in the Compare tab for each color setting.

Color Status

Red

Fail

Green

Pass

Yellow

Fail, but within 10% of the limit or 10% of the tolerance (see Parasitic Comparisons)

White

A supply net. These are not compared (but totals are reported)

Parasitic Comparisons

Parasitic comparisons are used to compare parasitics from the estimated schematic and extracted views. You can use these views to compare values for ~R, Coupled C, and Decoupled C on a net by net basis.

If you need to compare ~R, both estimated and extracted views need to be simulated before performing a comparison.
For information on viewing a comparison report see Comparison Reports.

Some features and requirements when using parasitic comparisons include:

Accessing the Compare Parasitics Form

To access the Compare Parasitics form:

  1. Open the design under test (DUT) schematic that was used for simulation, or descend into the DUT, before opening the Compare Parasitics form.
    In the case of the DUT, you must add tests which simulate the two parasitic views. These can be separate tests or different instances in the same test. The parasitic comparison flow is highly flexible in that it will search the simulation results to retrieve the required views.
  2. Select Parasitics/LDE – Compare to display the Compare Parasitics form.
    Figure 2-44 The Compare Parasitics form

Note:

GUI Item Description

Comparison Method

Controls how the estimates and extracted parasitics are compared.
- Estimates are upper limits

Specifies that estimates must represent an upper limit.
- Estimates are targets with tolerance +/-

Specifies that estimates represent a target. Here, you can specify a positive (or upper) and negative (or lower) percentage tolerance within which extracted parasitics must fall.

Parasitics to Compare

Selects which classes of parasitics should be validated and compared.
- ~R

Specifies that ~R (effective resistance) parasitics are to be compared.

If you do not check this option the ~R Simulation Data fields will be disabled. Not checking this option also means that you are not required to run any DC oppoint simulations.
- Coupled C

Specifies that coupled capacitance parasitics are to be compared.
- Decoupled C

Specifies that decoupled capacitance parasitics are to be compared.
- Self C

Specifies that coupled capacitance parasitics between segments of the same net are to be compared.

View Names and ~R Simulation Data

Specifies what view is to be the Target/Limit for comparisons.

See also Simulation Data.
Target/Limit

Specifies the parasitic/LDE view name to be compared.
~R Simulation Data

Specifies the simulation results to be used for the parasitic/LDE view (only enabled if ~R values are to be compared).

The table is populated with entries from the result history. From here, you should locate the results for the simulation made using the parasitic/LDE view. To help locate this only those results from a Spectre or UltraSim DC oppoint simulation of the current design is included in the table. The form will also filter results so that only those results for simulations containing the chosen estimate view will be displayed.
Actual

Specifies the extracted view name to be compared.
~R Simulation Data

Specifies the simulation results to be used for the extracted view (only enabled if ~R values are to be compared).

The table is populated with entries from the result history. From here, you should locate the results for the simulation made using the parasitic/LDE view. To help locating this, only those results from a Spectre or UltraSim DC oppoint simulation of the current design is included in the table. The form will also filter results so that only those results for simulations containing the chosen estimate view will be displayed.

Power and Ground Nets for Decoupled Capacitance

Use this field to set power and ground nets.

This field will initially be populated from the estimated/extracted setup.

Parasitic aware design uses these to determine which parasitic capacitances are decoupled (one side of the capacitor is connected to a power or ground net) or coupled (the capacitance is between two other nets).
- Net Names

Identify those power and ground nets that you want to use when differentiating between coupled and decoupled nets.

When entering a net name, you can optionally add a “/” at the beginning of each net name. If omitted, the “/” is automatically added when comparing nets.
- Select From Schematic

Select the power and ground nets directly from the schematic rather than physically typing them in.

Running DC Oppoint Simulation for Comparisons

Before attempting to perform a parasitic comparison you have to run a DC oppoint simulation for both the estimated parasitic/LDE view and the extracted layout. This enables parasitic aware design to calculate and compare effectiveR values for the two views. If you do not want to compare ~R resistance values a DC oppoint simulation is not required.

For information on running a DC oppoint analysis see Setting Up Analyses in the Virtuoso ADE Explorer User Guide.

When the Compare Parasitics form is opened, parasitic aware design searches all views of the current cellview (the DUT) looking for the parasitic/LDE and extracted views. The Estimated View Name and Extracted View Name pull-downs are populated so that only the parasitic/LDE views are listed in the estimated pull-down and extracted views listed in the extracted pull-down. Parasitic aware design then searches the data history for simulation results that contain the estimated and extracted views. If you change these views the simulation results will be re-filtered to show results from these views.

Simulation Data

The ~R Simulation Data sections in the Parasitic Comparison form contains a tree level structure that displays information on three levels:

  1. The top level contains the history entry name (for example Interactive.4).
    See also the Data assistant in the Virtuoso ADE Assembler User Guide which will also lists the history entry name.
  2. The top level expands to detail a list of tests that have been run (again this information is detailed in the Data assistant).
    If a single test is used to simulate both parasitic/LDE and extracted views, but only one view had one instance of the design in the test then you will have to simulate twice, changing the configuration in between (which is done using the Run Simulation assistant - see the Virtuoso ADE Explorer User Guide. This is so that the first simulation will be bound to the parasitic/LDE view, and the second bounded to the extracted view or vice versa.
  3. Expanding each test displays a list of instance paths to the estimate/extracted views (normally this will only be one instance path as there will only be one instance of a particular cellview in a design).
    It is not necessary for instance paths to match (between estimated and extracted ~R Simulation Data).

Comparing Estimated Parasitics With Extracted Parasitics - Summary

  1. If you want to compare ~R parasitics you need to perform a DC oppoint simulation for both the estimated and extracted views to be used.
  2. Open the schematic (design under test (DUT)) or the configuration used for simulation.
  3. Descend to where the parasitic estimates were placed.
  4. Select Parasitics/LDE – Compare.
    This will display the Compare Parasitics form.
  5. Specify a parasitic Comparison Method so that the estimates will either represent a limit (Estimates are upper limits) or a target (Estimates are targets with tolerance).
    If you select estimates to be a target you must specify a positive (upper) limit percentage and a negative (lower) percentage tolerance within which extracted parasitics must fall.
  6. Select which classes of Parasitics to Compare (~R, Coupled C, Decoupled C, and/or self C).
    If you do not select ~R, the ~R Simulation Data fields will be disabled.
  7. Specify the estimated and extracted views to be used for parasitic comparisons and the ~R Simulation Data, if necessary (see also Simulation Data).
  8. Click OK to perform the parasitic comparison.
    This will generate a compare report (see Comparison Reports) which will list the estimates along with extracted value and status (PASS or FAIL).

Comparing Against a Refined Extracted View

Rather than use the original extracted view you can also compare estimates against a refined extracted view.

In this case, the Estimated View Simulation Data for R Calculation section in the Compare Parasitics form requires that you specify the refined view to be simulated rather than the original, extracted view.

Comparing Capacitance

Capacitance is compared by summing all coupled capacitors and summing all decoupled capacitors on each net. Nets that have no estimates will be ignored.

Comparing Resistance

Parasitic effectiveR values are calculated for all nets in the estimated and extracted views.

The Parasitic Mode Toolbar

Use the Parasitic Mode toolbar to change the parasitic mode so that you can update all tests to point to the parasitic view for that mode. This means that you can simulate with estimated parasitics, extracted parasitics, or no parasitics, just by switching modes.

In addition, all device parameters are modified to use the parasitic/LDE view when in Schematic Estimates (Parasitics) mode. This means that you can sweep device parameters in the presence of your estimated parasitics.

Figure 2-45 The Parasitic Mode Toolbar

Any signals to be saved or plotted are automatically mapped to the estimated/extracted view when you change to either the Schematic Estimates or Extracted run modes.

Whenever you change the parasitic mode, the config view of the testbench is automatically updated to bind the cell to an appropriate view. For example, for the Extracted parasitic mode, the cell is bound to the available extracted view. Similarly, for the Layout parasitic mode, it is bound to the available netlist_layout view. A corresponding warning message is also displayed in the CIW.

For example, to simplify the simulation of parasitic estimates:

  1. Select Window – Toolbars – Parasitic Mode to display the Parasitic Mode toolbar if it is not already on view.
  2. Select Schematic Estimates (Parasitics) from the Parasitics pull-down.
    This will enable the other options on the Parasitic Mode toolbar.
  3. Select the Setup Parasitics button to display the Setup form.
  4. Complete the Setup form as required (see Parasitics/LDE – Setup).
    You can now create the parasitic/LDE view.
  5. Select the Build Parasitic/LDE view button to display the Build Parasitic/LDE View form.
  6. Complete the Build Estimated View form as required (see Parasitics/LDE – Create Filters).

Once you have successfully built the estimated view, you can open the testbench configuration to confirm that it has been re-bound to the estimated view. You can then choose to Run Simulation from the Simulation toolbar. For more information on Run Simulation see the Virtuoso Analog Design Environment XL User Guide.

Applying Sweeps from the Parasitic Mode Toolbar

The Sweeps drop-down option, in the Parasitic Mode Toolbar, allows you to choose whether to sweep parasitics and/or device parameters during simulation. This allows you, for example, to sweep estimates during a sensitivity analysis to find out how sensitive your design is to parasitics.

Figure 2-46 Sweeps on the Parasitic Mode Toolbar

Parasitic sweeps are only supported in Schematic Estimates (Parasitics) mode. It is not possible to sweep extracted parasitics.

Virtuoso Parasitic Aware Design creates parasitic parameters in the Parasitics tab of the Variables and Parameters assistant (for information about this assistant, see the Virtuoso Analog Design Environment XL User Guide) for each parasitic sweep that you have entered (see Entering Parasitic Sweeps).

Selecting a value from the Sweeps drop-down, on the Parasitic Mode Toolbar, controls device and parasitic parameters as follows:

For information about enabling or disabling individual parasitic parameters, see Enabling and Disabling Parasitic Sweeps.

Global variables are also enabled or disabled as appropriate if they specify a sweep. Global variables that appear in estimates are treated as parasitic parameters. Variables that have been used as a device parameter in the schematic are enabled and disabled along with other device parameters.

Parasitic Probing and Ultrasim

It should be noted that from MMSIM 7.1 onwards, Ultrasim includes, by default, certain reductions on parasitics in the netlist. While this can provide an improvement on the simulation time, a potential side-effect is that parasitic probing may not work on all parts of a design.

This issue can be avoided by controlling Quantus QRC parasitic reduction in the QRC Parasitic Extraction form, ensuring that the reductions are done at this point. To achieve this, you should enable the Reduce Parasitics option and specify a Reduction Frequency. For more information see the Quantus QRC Extraction Users Manual.

An additional method to avoid this issue is to prevent Ultrasim performing the reductions by requiring it save all the node information. This can be done using Outputs – Save All in the Test Editor.
If you set “.usim_opt preserve=1”, in Spectre, this can force Ultrasim to preserve all resistors (for more information, see the Excluding Resistors and Capacitors from RC Reduction section of the Virtuoso Ultrasim User Guide.

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