Knowledge Booster Training Bytes - Routing Techniques for Custom IC Layout Design in Virtuoso Layout Suite

In this Knowledge Booster blog, we talk about the different routing styles we have in Virtuoso Layout Suite XL and higher tiers for Custom IC layout design. We also introduce you to the videos and training materials that can help you understand and use these features.

Would you like to know the importance and learn about the routing techniques in Virtuoso Layout Suite?

You can use the routing techniques to speed-up routing in the layout design. Virtuoso Layout Suite has Virtuoso Interactive and Assisted Routing and Auto-route options.

The interactive routing lets you complete the critical nets before automatic routing and finishes the incomplete nets left unrouted after the automatic routing. The Virtuoso Interactive and Assisted routing feature lets you route the connections interactively within the Virtuoso environment to meet the critical design constraints and rules. The interactive and automatic routing abilities are enabled on all process nodes, including the most advanced process technologies.

The following are the commonly used routing techniques in Virtuoso Layout Suite:

• Differential pair routing
• Stranded routing
• Point-to-point routing
• Pin-to-trunk routing
• Shield routing

Differential pair routing: A constraint-driven routing technique in Virtuoso Layout Suite that is used to create a balanced transmission routing system to carry differential (equal and opposite) signals across the design. You can do this by routing the nets parallelly from the source pin to the destination pin.

Visit the Differential Pair routing demo video training byte to learn more about this routing technique.

Stranded routing: Stranded routing lets you increase the current capacity between two points, creating smaller pathSegs next to each other instead of large pathSegs. At the same time, it also controls resistance and metal density. This feature is available in Layout XL and higher tiers.

The create stranded wire command lets you create a wire comprising multiple strands in a single direction on a single net and works without specifying a constraint in the Constraint Manager. This kind of routing can be created from an empty space, an existing pin, an existing wire, or via, and an existing width spacing pattern.

To learn more about stranded wiring, visit the Stranded routing demo video Training Byte on the support site.

Point-to-point routing: The point-to-point command is an interactive routing command that automatically generates routing between two digitized points, which can be the two click points. The two points can overlap a pin, instpath, pathseg, path, existing wires, or vias, or can be an empty space. This routing technology allows you to break long connections into several shorter point-to-point links.

To learn more about Point-to-Point routing, visit the Demo on the Point-to-Point routing command video.

Also, you can visit Virtuoso Layout Pro: T5 Interactive Routing(XL) course from the Cadence Learning and Support Portal.

Pin-to-trunk routing: The pin-to-trunk routing style connects an individual pin to a trunk. Only the connections that are within the scope of a trunk are routed. The custom/digital routing style manually completes the remaining opens. This kind of routing is required when a spine structure is required, and it lets you add connections from the pins of devices and macro instances to the existing trunks.

See Virtuoso Pin-to-Trunk Routing Basics (video channel) to learn more about pin-to-trunk routing.

Also check out the Virtuoso Connectivity-Driven Layout Transition course from Cadence Learning and Support Portal.

Shield routing: Shield routing adds shield wires around the signal nets to improve signal integrity. For a shield routing to perform correctly, the "shield" net must have a signal type of either "power" or "ground."

To create a shield net and achieve proper shield routing, define the shield constraint, select the shield style, and then tie the shield wires. In Virtuoso Layout Suite, we have three types of shielding styles available, they are:

• Parallel symmetric shielding: This adds planar shield wires parallel to the signal wires.
• Tandem shielding: Tandem shield wires are added on a layer above and a layer below the signal wire layer.
• Coaxial shielding: Coaxial shielding adds tandem and parallel shield to surround signal wires in four directions.

To know more about shield routing, see the Demo on Shield Routing technique on the support portal.

Please note that there are also Digital Badges available for the trainings mentioned in this blog.

Related Resources

Product Manuals	Virtuoso Space-based Router User Guide Virtuoso Interactive and Assisted Routing User Guide
Rapid Adoption Kits	Virtuoso Space Based Router RAK
Training Bytes	Routing Techniques in Virtuoso Layout Suite
Online Courses	Virtuoso Connectivity-driven Layout Transition Virtuoso Layout Pro: T5 Interactive Routing(XL)

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Knowledge Booster Training Bytes is an online journal that relays information about Cadence Training videos, online courses, and upcoming webinars that are available in the Learning section of the Cadence Learning and Support portal. This blog category brings you direct links to these videos, courses, and other related material, on a regular basis. 

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