open access layout web page header


Open Access and PCELLs

PCELLs (Parametric Cells) were developed by Cadence for use in their layout editor Virtuoso. A PCELL is created using the SKILL programming language and allows the user to specify one or more parameters from which a cell is generated.

pcell flow for Cadence Virtuoso

PCELLs are widely used in analog design since many analog functions are scalable and their are entire libraries of PCELLs designed and optimized for particular analog processes.

While this is very efficient for the designer it makes interoperabilty a serious problem since the SKILL language used to create the PCELLs is proprietary to Cadence. Therefore another layout editor or viewer or any tool that must use the layout is unable to evaluate the PCELL instances that are placed into the OA database.

From Cadence's point-of-view this is not a bad thing but for anyone who wants or needs to interface with Virtuoso, PCELLs are very problematic -- even more so because Virtuoso is the dominant tool used for analog IC design.


In order to address this issue a number of other EDA vendors have organized to support PyCells. These are also parameterically generated cells but instead of using a proprietary programming language they use the open source Python language to implement the cell. This means that any EDA vendor who wishes to do so can offer parametric cells and that others can then evaluate such cells.

PyCell flow for Open Access

A company called CiraNova has created a PyCell implementation for Open Access.

Ciranova also offers a product, Pcell Xtreme that can evaluate Cadence PCELLs (but which requires a Cadence Virtuoso license to do so in order to access the SKILL programming language.)

How Does This Affect Qckvu3's Open Access Viewer?

How this affects Qckvu3's OA viewer depends on your need for PCELL support. There are three possibilities:

  1. No PCELL or PyCell support Needed
  2. Only PyCell Support Needed
  3. Full Cadence PCELL Support Needed

Case 1 - No PyCell or PCELL Support

This case is simple. Just install Qckvu3 and start using it on Open Access databases.

Case 2 - PyCell Support Needed

In this case you will need to download and install PyCell Studio. The download is a free one - Ciranova charges for support if you need it but not for the actual code.

Case 3 - PCELL Support Needed

In order to support Cadence PCELLS you will need both: a Cadence Virtuoso license (V6.13 or later) and Ciranova's PCELL Extreme software. Installation is complicated. More details and scripts are provided.

OA Main Page Download Price Revision History

417 Ingalls St., Santa Cruz, CA 95060    Tel (831) 426-6163     Fax 426-2824    email: