Modgen Merge Wells
Merging of wells in Modgens is controlled by the mergeLayer parameter in the Modgen ci constraint. The default value for the mergeLayer parameter in Modgen is default. For backward compatibility with the 614 Modgen constraints, the modgenMergeWells environment variable can be set in the .cdsenv file.
If this environment variable is set to t and the mergeLayer parameter is set to default, the wells of the Modgen instances are merged. However, if the environment variable is not set, and the mergeLayer parameter is set to default, the wells in the Modgen layout are not merged.
Other possible values of the mergeLayer parameter are: none, well, and any other custom layer, which can be selected from the Constraint Manager GUI. If mergeLayer is set to none, there is no well merging in the Modgen. If mergeLayer is set to well, the wells of the Modgen devices are merged and any DRCs between well layers and other layers of the devices are ignored. If mergeLayer is set to a custom layer, such as Oxide_thickness, the shapes on that layer are merged and DRCs between that layer and other layers of the devices are ignored.
In addition, you can merge multiple layers, such as Nwell and Oxide_thk. Before merging layers, only the top-level net connectivity between the layers is checked. So, layers across devices that have different master Pcells can also be merged. An example for well merging is shown below:
To specify whether the analog placer should have control over the well and body contact geometry, set the aapDefaultWellsUnderPlacerControl environment variable to t.
The merge layer functionality differs when there is a pane guard ring inside the Modgen structure. A layer across a pane guard ring is merged only if one of the following situations is applicable.
- The layer is defined as a recognition layer in the technology file.
- The layer is a well layer with the same net connectivity across all devices and the pane guard ring.
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