Electronic Design

Persistent PCells Click With OpenAccess

Do time-based licensees of EDA flows really own their layout data? Not unless they convert it into a format like GDSII. Without licenses, proprietary databases are just clumps of locked binary data. Today’s designers must maintain licenses to access legacy design data. This is the reason for the popularity of formats like Verilog, SDC, GDSII, and LEF/DEF for design data. Designers need open standards and database access to ensure access to their design data.

But how does this apply in the analog and custom design domains? Today’s parameterized layouts lose much of their valuable content when converted to GDSII since the device parameters are discarded.

Even if the future is OpenAccess, with its open-source model, it is not enough to solve the problem. A layout using a proprietary evaluator like SKILL or non-open-source libraries is as locked as a binary database without a license.

What is being done to help customers gain better access to their data? Persistent PCells are a mechanism on OpenAccess that enables PCell data to be hardened, removing the dependency on proprietary languages and libraries (see the figure). The key difference is no data loss.

When data is brought back to the system that created it, the hardening is inverted without any data being lost, allowing parameterized editing to continue. This is not the case with GDSII, because once a parameterized entity is converted, most data is lost and inversion to a parameterized form is impossible.

PCells work by taking a software description of a layout and converting it to geometries based on unique instance parameters. Today’s legacy systems always image the layout through the software. This creates two core problems.

One problem is dependency on proprietary libraries and languages. The second is speed, a problem that grows with design size and complexity. Legacy languages are used to image from hundreds to thousands of unique PCells each time the design is opened.

These languages are 100 times slower than modern scripting languages like Python and thousands of times slower than C++.

Persistent PCells for OpenAccess provide the means to remove the software from the layout while retaining parameter inputs and hardening the output. Layout editing environments such as the RDE Framework from Silicon Navigator cache PCells all the time, reevaluating only when parameters or layouts change.

Operating speed on this kind of layout is as fast as operating on GDSII data, which saves weeks of valuable time on large, complex mixed-signal designs. PCell persistence and OpenAccess will give customers the data ownership they need while providing higher layout performance for ever increasingly complex layouts based on parameterized cells.

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