Interactive Transistor Folding
Interactive folding might overwrite the default folding threshold value using the specifications you supply. For example, if you divide the transistor into too few folds, each fold might end up longer than the folding threshold value you specified for the component type. Automatic folding always respects the folding threshold value.
If you enter a folding threshold value that would yield a device with more than 999 folds (for example, a device width of 2 and folding threshold of1μ, which can result in a device folded into 2M folds), the CIW prints a warning and does not fold the device. You can still fold such a large device manually.
Interactive folding supports a maximum number of 500 folds to be generated for a device. Specifying a value greater than 500 issues a warning message in the CIW and no folding is performed.
Interactive folding rounds the width values using the rounding values specified in CPH to provide the accurate Total Width and individual width values prior to creating devices in the layout. For example, assume you have a device |P0 with w = 3u and CPH Rounding = (w 0.5u round). If you fold |P0 into 7 folds with equal widths, each width in the form will be displayed as 428.571429n. Now, if Rounding is applied when the devices are placed in the layout, the width of each folded device is set to 500n, making the form widths inconsistent with the device widths in the layout.
Instead, if the interactive folding uses the CPH Rounding value to round the width values at the time of the initial calculation, the form widths achieved are consistent with the layout widths. This provides a more realistic and reliable fold width information before the actual creation.
Interactive folding always considers the parameter that sets the device width in the source, even if you have specified that this parameter is to be ignored in the paramsToIgnoreForCheck environment variables.
To keep folded devices from becoming off-grid, set the Rounding option in the Configure Physical Hierarchy window.
When folding FinFET devices, folding can be driven by the Number of fins parameter or the Width parameter set on the devices that are selected for folding. When folding based on Number of fins, the Generate Folded Devices form displays the folding values in fins instead of width.
Interactive folding can retain folded devices as selected even after the devices are placed in the layout canvas. This behavior can be controlled using the retainSelectionSet environment variable.
Related Topics
Folding a Multi-fingered Device to Create Split Fingers
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