Virtuoso XL Layout Editor User Guide

Using the Virtuoso Custom Placer

Important

Using mixed methods to create constraints is not recommended. To avoid problems resulting in conflicting and redundant constraints, creation of pin constraints may be performed in either of two ways:

Use the Pin Placement form exclusively or

Use the constraint manager and constraint manager SKILL functions exclusively

For information about setting constraints using the constraint manager or the constraint manager SKILL functions, refer to the Virtuoso Constraint Manager User Guide or the

Custom Layout SKILL Functions Reference Manager User.

Constraint Limitations

■Virtuoso custom placer does not support Virtuoso constraint manager net-based constraints

■Constraints must be entered at the top level schematic or layout

■The constraint manager and the Pin Placement form, if used at the same time, can create conflicting constraints.

Placement Parameters and Component Types

You control how components are assigned to rows, and their chaining and folding parameters, by defining component types. Set the component type parameter using the Edit Component Types which appears when you choose Design – Component Types.

If you edit component types created in IC 4.4.6, using an editor in IC 5.0.0 or later, the data will be saved a in a new format that is incompabitle with IC 4.4.6.

Virtuoso XL Layout Editor User Guide

Using the Virtuoso Custom Placer

Defining Component Types

Important

For row-based placement styles, defining component types is mandatory. The purpose of defining component types is twofold:

■To identify PMOS and NMOS devices to enable chaining and folding

■To identify groups of devices for row-based placements

Note: Currently there is no need to define component types for devices that will be placed by area. Only assign component types for devices that will be placed within rows.

Component types are part of the library, cell, or reference library information for cells in which components are placed. You can define component types at the library level, if all cells in the library share the same types, or you can define component types for the individual cells that will contain the placed components. This allows you to define a set of types common to all designs in a library and override these for a selected set of designs.

Devices are placed within the prBoundary regardless of their component type unless;

■Devices have been locked in place

■The Place Selected Objects Only option is specified in the Auto Placer form.

Important

If the placer does not place a component in the rows, verify that the lxComponentType parameter has been assigned to the component and that the row definition allows for that particular component type to be placed.

MOS Transistor Chaining and Folding Parameters

MOS transistors that are candidates for chaining and folding need to have the lxComponentType parameter set with certain values.To set the lxComponentType parameter, use the Edit Component Types form.

Important

Use the following parameters in the NMOS or PMOS type definitions to control device chaining and folding during placement. You must set the lxActiveLayers, lxDeviceWidth, lxMaxWidth, and Component Class parameters; the other parameters are optional.

Virtuoso XL Layout Editor User Guide

Using the Virtuoso Custom Placer

Note: Terminal names are not case sensitive.

Required Parameters

Active Layer The active layer is required to find the spacing value between components (NMOS or PMOS) diffusion layer.You must enter the layer purpose pair for the active layer of the given MOS device type. The Placement Planning form uses the layer purpose pair to look up from the technology file the spacing rules for the diffusion layers, and use it to seed the defined spacing type in fields on the Assisted CMOS form.

The Update Estimate command for Assisted CMOS placement takes the spacing rule between adjacent MOS device chains into account, yielding more accurate estimates.This parameter must be used in the NMOS or PMOS type definitions to control device chaining and folding during placement.

If the Component Class is set to either PMOS or NMOS, and no value has been set for lxActiveLayer, a message will appear in the ciw informing you that the lxActiveLayer must be set.

Width Par Name The name of the transistor width parameter on the device master cell.

If not set, the assumed default name is w. If you use a different name for the width, set this parameter to the correct name.

Fold Threshold The maximum width beyond which devices of type NMOS and PMOS will be automatically folded when folding is enabled. If you do not set this parameter, devices are not folded. This parameter must be used in the NMOS or PMOS type definitions to control device folding during placement.

This value applies globally to all devices within the scope of the component type definitions (the library containing the current cell or just the current cell). In the Placement Planning form, you can override lxMaxWidth by setting PMOS Width Threshold and NMOS Width Threshold. This parameter must be used in the NMOS or PMOS type definitions to control device chaining and folding during placement.

Virtuoso XL Layout Editor User Guide

Using the Virtuoso Custom Placer

Virtuoso XL cannot accurately enforce the value of lxMaxWidth unless all device widths and all lxDeviceWidth values are specified consistently; for example, all in meters (10um is 1-e-5) or in all user units (10um is 10).

Component Class This must be set to either NMOS or PMOS to allow the Virtuoso XL

Layout Editor and the Virtuoso Custom Placer to identify the P and N

MOS device types for folding, chaining, and assisted MOS operations.

Optional Parameters

Bulk Terminal A list of bulk terminal names. If not set, the assumed default names are bulk and B.

Drain Terminal A list of drain terminal names. If not set, the assumed default names are drain and D.

Gate Terminal A list of gate terminal names. If not set, the assumed default names are gate and G.

Defining Components Types

1.Choose Design – Component Types.

2.In the Edit Component Types form, specify that the properties will be set for the Library,

Current (cell level), or Ref Libs.

When you select Ref Libs the reference libraries are listed in the cyclic field.

Important

The Ref Libs settings are read first. If there are noRef LIbs settings, then Library settings are read next. Current settings will override LIbrary and Ref Libs settings.

3. In the Types field, type the name of the type you will be using.

Virtuoso XL Layout Editor User Guide

Using the Virtuoso Custom Placer

Types are user defined. Previously defined types appear in the cyclic field above the text

field.

4.Click Add to add the type to the Type cyclic field.

Once a type is displayed in the Type cyclic field you cannot specify which cells will be assign that component type.

5.From the Cells in Design list box, select the cells by library/view name and click the arrow button to move them to the Components in Type list box.

6.Specify from the cyclic at the bottom of the form the “Component Class” the group of cells belongs to.

Undefined

PMOS

NMOS

STDCELL

STDSUBCONT

FILLER

Component classes PMOS, NMOS, STDCELL, and FILLER will all be evaluated by component-assisted row generation. Use PMOS/NMOS if you are running MOS component-assisted row generation. Use STDCELL if your running Standard Cell component-assisted row generation. Use both if your using a combination of placement modes.

Note: Choose Undefined if the device is none of the others.

For component-assisted row generation, you should have component types and the component class assigned to cells. Otherwise those cells will not be included in the automated row generation.

7.For PMOS and NMOS types specify values for WidthParName, Fold Threshold and Active Layer for chaining and folding to occur.

8.Optionally, for PMOS and NMOS supply the following properties if they are different from the default names.

Source Terminal Drain Terminal Gate Terminal