Virtuoso XL Layout Editor User Guide

Preparing Your Connectivity Source for the Virtuoso XL Layout Editor

envSetVal(“layoutXL” “ignoreNames” ‘string “vxlIgnore lvsIgnore ignore nlAction”)

Note: A schematic device that has the string property nlAction with a value of ignore behaves the same as one with an lvsIgnore or ignore property.

Using the lxlgnoredParams Property to Exclude Device Properties

Virtuoso XL maintains in the layout the value of parameters and the properties of devices in the schematic.

If there are devices in your schematic with properties that you do not want to be checked when you use the Connectivity – Check – Against Source command or transferred to the layout when you use the Connectivity – Update – Layout Parameters command, specify those device parameters to be excluded using the lxIgnoredParams property.

You can also set this property on layout components that are the same except for their parameters, so that the differing parameters are ignored by the cloning functionality.

The lxIgnoredParams property has the type string and takes as its values the names of the properties that you want Virtuoso XL to ignore.

You can define thelxIgnoredParams property as

■A property of the symbol instance in the schematic

(add the property to the symbol just as you do the lxUseCell property)

■A property of the symbol master in the library

(add the property to the master just as you do the lxUseCell property)

■A property of the device instance in the layout

(add the property to the instance just as you do the PermuteRule property)

■A component description format (CDF) using the Command Interpreter Window (CIW) Tools – CDF – Edit command (add lxlgnoredParams as a CDF parameter just as you do the lxUseCell property using the names of the properties you want to ignore as the defValue)

Using the lxRemoveDevice property to Ignore Parasitic Devices

The lxRemoveDevice property should be attached to an instance/master in conjunction with an “ignore” propertylvsIgnore( or aulgnore). If the device is ignored, the lxRemoveDevice property is considered.

Virtuoso XL Layout Editor User Guide

Preparing Your Connectivity Source for the Virtuoso XL Layout Editor

the lxRemoveDevice property has the type string. You can define thelxRemoveDevice property as;

property name: lxRemoveDevice

property type: string

property format: “(short(term-list)...[function({arguments})])”

Where short is a keyword, term list is a space separated list of terminal names (no quotes around the names. Function is a SKILL function which is evaluated to decide whether or not the device will be removed or not based on the optional arguments each of which must be “instance” parameters.

The following merging rules are used In deciding which net will survive after the device is shorted.

1.Global nets or nets connected to I/O pins will always survive.

2.If global or external nets do not exist, then the net at a higher level of hierarchy will survive. For example, net1 will survive over /I1/net2.

3.If the nets are at the same level of hierarchy, the net with the shortest name will survive. For example, netA will survive over netBCD.

4.If the nets are at the same level of hierarchy and are of the same length, alphabetical order is used. For example, netM will survive over netN.

Rules for the lxRemoveDevice handling:

1.One single function applies for all the short() lists.

2.If the function is missing, the terminals will be shorted as specified in the short rule.

3.If the device is not removed, the terminals are not shorted.

4.A warning is issued when the device is not ignored in the netlisting.

5.If the lxRemoveDevice property is missing, the ignore Property is honoured and the ignored instance connections are left open.

lxRemoveDevice Example

For a resistor with terminal names PLUS and MINUS, a simple lxRemoveDevice property can be:

Virtuoso XL Layout Editor User Guide

Preparing Your Connectivity Source for the Virtuoso XL Layout Editor

(short(PLUS MINUS))

This will short the terminals always, as long as this device is ignored (lvsIgnore or auIgnore, etc.)

(short(PLUS MINUS) funcR(r))

In this case, the resistor will be shorted only if the device is ignored AND user defined SKILL function "funcR" returns non-nil.

Important

The arguments to the function must be instance/cell parameters names. VXL will replace the names with the evaluated values of the properties when calling the function.

Don’t miss the initial and final parentheses. They are needed.

The function must already be defined. The recommended place to define this function is in .cdsinit or libInit.il files. A sample funcR for the above case can be defined as:

procedure( funcR(r)

if(r<100 then t

else nil)

)

Using the lxViewList and lxStopList Properties to Prepare Hierarchical Designs

To prepare a hierarchical design for use with Virtuoso XL, you must make sure the symbol for each top-level design element is mapped to the correct lower-level design element for layout generation.

To map one cell to another cell,

■You can add the lxUseCell property to an instance of a cell, or you can add the lxUseCell property as a CDF parameter to a cell

■You can use the lxViewList and lxStopList properties to specify which layout view to use

Virtuoso XL Layout Editor User Guide

Preparing Your Connectivity Source for the Virtuoso XL Layout Editor

The lxViewList property creates a switch view list that tells Virtuoso XL where to look for the view name of a cell on the lower levels of a hierarchical design. The default value is schematic netlist symbol layout compacted symbolic.

The lxStopList property creates a stop view list that tells Virtuoso XL where to stop looking; that is, it identifies the view with the most detailed description or the one with no further layers of hierarchy as the stop view. The default value is layout compacted symbolic.

For a more detailed explanation of hierarchy expansion using the lxStopList and lxViewList properties, see “How the Netlister Expands Hierarchy” inChapter 3 of the

Cadence Analog Circuit Design Environment User Guide.

Note: In releases 4.3.4 and earlier, the maskLayoutViewName property specified which view to use in the layout. Virtuoso XL still recognizes this property if you have not defined the lxStopList property.

Setting the lxViewList and lxStopList Properties

You define thelxViewList and lxStopList properties just as you define the lxUseCell or any other property:

■As a property of the symbol instance in the schematic

■As a property of the symbol master in the library

■As a property of the device instance in the layout

■As a component description format (CDF) parameter of the layout device

After generating a layout, you can change the view using the layout window Connectivity – Change Instance View command. The Change Instance View form lets you choose a view from the list defined in thelxStopList property.

The following figure represents the schematic hierarchy and shows which layout views Virtuoso XL chooses under these conditions:

■lxStopList is set to layout layoutS

■lxViewList is set to schematic cmos.sch

Virtuoso XL Layout Editor User Guide

Preparing Your Connectivity Source for the Virtuoso XL Layout Editor

The chosen layout views are shown with thick-line boxes.

chosen layout view

Top Cell

In this figure, as Virtuoso XL builds the layout, it looks at each symbol in the Top Cell.

The Mux cell has no view listed in the stop list; therefore, Virtuoso XL goes to the view list and switches into the Mux schematic. All devices in the Mux schematic have views that are in the stop list; therefore, Virtuoso XL places those views.

The AND cell has a view listed in the stop list; therefore, Virtuoso XL places that view and never switches into the view list.

Overriding the stopList Property

If you want to descend into a device through a particular instance where the master has the lxStopList property defined, but you want to descend all levels further down, you can set the value of the lxStopList property to an empty string (“ ”).