lxCombination Property

lxCombination string t_expression

Description

Builds a complex set of devices comprising series (sfactor) and parallel (mfactor) connections.

You typically use lxCombination to split a single resistor into multiple smaller devices in order to achieve maximum density in the layout by placing devices in spaces otherwise not utilized. This lets you approximate the resistance value defined in the schematic without violating the manufacturing grid.

The lxSeriesTerms Property property must be defined on the instance in the schematic in order for Layout XL to understand the connectivity of devices with sfactor >1 and instance terminals>2.

Symbol master Add Property form
Name	lxCombination
Type	string
Value	t_expression

Add CDF Parameter form
Add After Parameter	As First Parameter
paramType	string
name	lxCombination
defValue	t_expression

Example

In a schematic cellview, a resistor called A with resistance 3k is connected to net1 and net2, and has the following lxCombination expression defined.

(2k*2)/3+1500/4

Where

• 2k, 2, 3, 1500, and 4 are device parameter values
• * and + are series connections (+ can be followed by an expression; * must be followed by an integer)
• / is a parallel connection (and must be followed by an integer)

During layout generation, Layout XL reads the lxCombination property, ignores the 3k value, and instead generates a total of 10 resistors: two 2k resistors connected in series, connected in parallel three times; and four parallel-connected 1.5k resistors connected in series to the 2k resistors.

Additional Information

• To ensure that lxCombination expressions are evaluated correctly, you must set the lxEvalCDFCallbacks environment variable to t before generating your resistors.
• You can also use lxCombination to define the topology for a network of capacitors. However, in this case, the property describes only the topology of the network; the values entered do not equate to the total capacitance of the network.
• If the lxCombination property is defined on the schematic symbol, the r parameter is ignored by the Generate All From Source and Update Components And Nets commands. The layout instances will have the correct parameters based on the lxCombination factor setting.
• Devices defined using lxCombination are named instName.msinteger in the layout. In our example above, if the schematic instance is called R0, the layout instances generated are named as follows.
  

  Schematic	Layout
  R0	|R0.ms1 |R0.ms2 |R0.ms3 |R0.ms4 |R0.ms5 |R0.ms6 |R0.ms7 |R0.ms8 |R0.ms9 |R0.ms10

  
  Nets associated with lxCombination devices are named instName.sinteger.expandedNetinteger in the layout.
  For example,

  R0.s1.expandedNet1

  where “expandedNet” signifies that the layout net has no real match in the schematic.

Related Topics

Setting Layout XL Properties

Layout XL Properties

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