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.