In this new age of complex designs and scaling of technology nodes, there are more number of wires per given square unit of area. As a result, applying constraints is considered wise to make sure signal integrity (SI) is taken care off well. It is due to this reason that circuit designers show a growing preference for using a larger number of constrained and managed nets. These constrained nets, if possible, can be used as it is or in a group with another set of constrained nets to define spacing with respect to another group or individual constrained nets. At this moment, have you ever thought that if the Constraint Manager assistant could offer this ability, your life as a circuit designer would be simplified and you would be able to face the challenge of tracking and handling such constraints in the design better?
Well, keeping this requirement in mind, the Constraint Manager assistant now provides two new constraint types, Net Class Group and Net Class Hier Group. Both these constraint types allow you to group one or more members belonging to the following routing-related constraint types: Diff Pair, Bus, Matched Length, Net Class, and Symmetry. A Net Class Hier Group constraint also allows you to do the following:
- Include Net Class Group constraints as a member.
- Create constraint directly on the constrained nets without a need to have groups.
- Define spacing to space out the constraint members at equal distance.
Using these constraints is extremely easy! Just select the required constraint types in the Constraint Browser and choose Net Class Group or Net Class Hier Group from the Constraint Creation–> Routing menu.
If a Net Class Group or Net Class Hier Group constraint already exists in the Constraint Browser, a simple drag and drop of a specific constraint type on it can help you to add a new constraint member. Guess what, you can add any number of members that you want to a Net Class Hier Group constraint and it will equally space out all its members. However, while adding new members, consistency checks will be performed to avoid spacing-related conflicts between the members of the Net Class Hier Group constraint especially when it contains a Net Class Group constraint.
The video excerpt below shows an example of creating a Net Class Hier Group constraint.
(Please visit the site to view this video)
You can view a full video on grouping and spacing out constraint members using a Net Class Hier Group constraint. Click the video link now or visit Cadence Online Support and search under Resources — Video Library for the video titled Creating Net Class Hier Group Constraints.
Note: If you don’t have a Cadence Online Support account, you can play the Creating Net Class Hier Group Constraints video (mp4) natively in Cadence Help when you are using Virtuoso IC6.1.7/ ICADV12.2 (ISR6 or later). In the Cadence Help Virtuoso Documentation Library, look under Video Demos for each of the videos in the series.
Related Resources
- Virtuoso Unified Custom Constraints User Guide
Note: For more information on Cadence products and services, visitwww.cadence.com.
Virtuoso Video Diary – What’s Next
Virtuoso Video Diary will next bring to you a video series titled - Staying XL-Compliant by Manipulating the Layout Hierarchy - that explains how it can sometimes help to take the unconventional route of desynchronizing the schematic and layout hierarchies, and still say Layout XL-compliant. This is possible with the enhanced Make Cell and Flatten commands, when used in Layout XL. Stay tuned to learn what being desynchronized, yet Layout XL-compliant means, what makes this possible, what are the situations to benefit from this, and finally, how does one make it happen…
About Virtuoso Video Diary
Virtuoso Video Diary is an online journal that relays information about Virtuoso videos that are available in the Cadence Online Support Video Library. For IC6.1.7 and ICADV12.2, over 100 videos on a wide variety of new and exciting Virtuoso features have already been created. Virtuoso Video Diary brings you direct links to these videos and other related material, on regular basis, in your mailbox. Subscribe to receive the e-mail notifications.
Abha Rawat