Manual Device Abutment

Device abutment is the process by which a number of MOS transistors (or the individual folds of folded transistors) are chained in a specific order. Chaining devices helps reduce layout area and capacitance.

Prerequisites Manual Device Abutment

The transistors to be chained:

• Need not be bound to a schematic instance.
• Must be properly set up for abutment.
• Must have the lxComponentType property set on the cell or library to which they belong. You set this property using the Edit Component Types command.

All parameter values are retained after chaining. The chaining engine always creates pairs of P and N chains with the P chain on top (because the power rail is typically at the top of a cell) and the N chain at the bottom (because the ground rail is typically at the bottom).

You can use the following commands to chain devices manually.

• Generate Chained Devices lets you chain devices interactively while you are editing a layout.
• The Chain command in the instance shortcut menu lets you chain devices selectively while you are editing a layout.
• Generate Selected From Source can automatically chain devices while generating a layout.
• Move lets you control chaining while moving devices.

The results generated by the chaining engine are affected by the setting for the lxStackPartitionParameters environment variable. The Generate Chained Devices command considers the first parameter of this environment variable only if there are 100 instances or more in the selected set. Generate Selected From Source always considers both parameters.

Related Topics

Pcell Set Up for Abutment

Component Types Mode in the CPH Window

Chaining Devices Interactively

Chaining Devices Using the Shortcut Menu

Chaining Devices when Generating Selected From Source

Moving Chained Transistors

lxStackPartitionParameters

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