3 Ways To Improve Design Collaboration: Part 3

The first two blog posts in this three-part series focused on the design team’s capability to communicate efficiently. An accurate to-do list is the basis of providing accurate estimates for project release schedules. The Cliosoft VDD (Visual Design Diff) tool is an effective way to maintain a live and accurate “to-do list” for design engineers and managers alike. Additionally, it provides the data for the management team to monitor progress and ensure the team is focused on the release schedule. In this blog post, we will examine the importance of collaborative design flow for schematics and layout engineers.

Schematic design engineers are a special breed of engineers who never give up the quest for perfection. They never give up “polishing the cannonball.” However, the economics of the project schedule demands that the schematic they are developing must be passed over to the implementation phase – the layout designer.

The design engineer has to identify the right time to pass it over to the layout designer. If the design is passed over to the layout designer too soon, the risk is that if the schematic changes significantly, the layout needs to be redone. From a project management perspective, this is an inefficient use of resources. The resources could have been useful on other priority projects. Conversely, if the design and layout phase do not have overlaps, there is a risk that the parasitics from the layout may force a redesign of the original design. This would prolong the project.

The optimal time for the handoff between the schematic design engineer and the layout engineer can only be determined by the talent and experience of the respective schematic and layout engineers involved. No tool or methodology can replace the skill of the design engineer to determine the handoff point.

However, a design flow can be put in place to ensure:

1. Design engineers have the liberty of “polishing the cannonball”
2. Layout engineers have a stable schematic design to implement (layout)
3. Design managers have the ability to prevent the team (design and layout) from unintentional edits

Cliosoft’s SOS design management system allows such a flow to be implemented with minimal effort. The flow is based on the out of the box features and customizable scripts that provide the automation for efficient collaboration between the design engineers and layout designers.

Imagine a common scenario where the design engineer is working on a precision op-amp schematic. Typically, the engineer starts with an initial design, likely from a previous project and modifies it for the current requirements. A  typical strategy is to handle the primary parameters like GBP, slew, and Iq to size the devices first. Then handle the secondary effects like signal integrity better in the next stage with the help of parasitics extracted from the layout. It is possible that the effects of the parasitic in the layouts may force major design changes. It is important for the design and layout to work in close collaboration and the design flow must enable this.

As the design engineer starts working and making modifications to the schematic design, a stage comes when they decide that the schematic is ready for layout. It is understood that the design is not finished but the layout engineer has a somewhat solid design to implement. The design engineer simply tags the schematic version as “RDY” indicating that it is ready.

The layout designer’s work area is configured to get the tagged version of the schematic. Meaning, if the design engineer creates a new version of the schematic, the layout designer will not get it in their work area. This provides the design engineer the liberty to make as many changes to the schematic as they please without affecting the layout process. However, if the schematic engineer deems it necessary for the layout designer to have a newer version of the schematic, they simply need to move the tag to the new version. The layout designer’s work area is already configured to receive the new version of the schematic – no email or phone calls necessary!

With a tagged schematic instead of the latest schematic in their work area,  the layout engineer has a stable schematic design to work on. It may take the layout designer a few days or perhaps a few weeks to layout that schematic, pass the LVS/DRC rules and run parasitic extractions that provide feedback to the schematic engineers for more accurate simulations.

The design engineer keeps receiving valuable feedback from the layout’s progress. It is entirely possible that the design engineer tags different versions of the schematics as “RDY” and the layout engineer implements it. Once set, the delivery of a stable layout to the layout designer is streamlined while the design engineer polishes the cannonball! Part 1 of this blog series demonstrates how the layout engineer has an accurate task list to keep track of.

Eventually, when the layout is ready and no more iterations are required, the layout engineer simply puts a “layout_done” tag on the design. Simple, customizable automation puts the same tag on the schematic. The reason to do so is that if all schematics in the chip are tabulated, it is easy to identify unfinished work.

The management team can lock down any further development by “freezing” the schematics and layout. This prevents feature creeps and also accidental edits. This is a handy mechanism for the design managers to keep their teams focused on development that contributes to keeping the project on track. The mechanism is especially useful in the ECO phases – as we highlighted in Part 2 of this blog series.

Typically, in the development cycle, the number of revisions of schematics and the number of revisions of layouts do not match. However, for traceability and debugging purposes it is important to maintain a link between a schematic version and the corresponding layout version. Traditionally, schematics and layouts have a “note” feature to keep track of this. However, it is inaccurate and relies on the discipline of every team member to keep a detailed track of the correlation. Cliosoft’s SOS design management solution provides a valuable feature of custom attributes to track such information. Whenever a version of the layout is tagged “layout_done”, a simple trigger can also associate the current version of the schematic with the version of the layout and vice-versa using a custom attribute. This creates a link between the schematic version and the layout version that can later be queried. This eliminates the need for schematic engineers and layout engineers to maintain records, enabling them to focus on their engineering tasks! If any further iterations to the cell have to be reverted, we can identify exactly which version of the layout is associated with the reverted version of the schematic.

In this 3-part blog series, we have highlighted the value of a design flow and tools to improve collaboration between schematic and layout engineers. Efficient and effective collaboration is necessary for the successful and timely completion of a design project. Visualization tools, automated flows, and clever reports help keep the team focused on critical design activities.