Chapter 9: Tools
9-2: Design Rule Checking (DRC)
9-2-1: Introduction to DRC

There are three built-in design-rule checkers: incremental, hierarchical, and schematic. After analysis of the circuit, you can review the errors by typing ">" and "<" to step to the next and previous error that was found. You can also see a list of errors in the cell explorer (see Section 4-5-2).

Incremental DRC

The incremental design-rule checker is always running, examining your layout, and issuing error messages when an error is detected. It checks only the current cell, and does not consider the contents of cell instances, lower in the hierarchy. It therefore offers an instant analysis, but not a complete one.

The incremental DRC also shows simple design-rules violations when a node or arc is being moved. See Section 2-4-1 for more on this.

Hierarchical DRC

The hierarchical design-rule checker uses the same rules and techniques as the incremental checker, but it checks all levels of hierarchy below the current cell. To run it, use the Check Hierarchically command (in menu Tools / DRC). To check only a selected subset of the current cell, use Check Selection Hierarchically.

When checking hierarchically, it may be the case that a cell is not designed to be checked in isolation, but must have higher levels of the hierarchy considered. For example, notches in the well areas may be covered at higher levels of hierarchy. When this happens, tell the DRC to ignore the cell by using the command Add Skip Annotation to Cell.

Schematic DRC

The schematic design-rule checker looks for issues that make drawing or editing of the cell difficult. These are the errors that is finds:

  1. Nodes:
  2. Arcs:

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