Gene’s Law Meets EDA

By Pallab Chatterjee
What will be the next major improvement that will cut power levels by an order of magnitude?

That question was the basis of a roundtable discussion at the recent ISSC conference. Current technology provides incremental improvements each year, but the next generation of electronic systems will require dramatic changes and innovation. This premise is based on Gene’s Law—that’s Gene Frantz of Texas Instruments—which states that the power efficiency for DSPs doubles every 18 months.

The roundtable consisted of six panelists from TSMC, Hitachi, STMicroelectronics, UCLA, Infineon, and an industry veteran consultant. The interactive challenges were posed by domain experts from Imec, the University of Tokyo and Stanford University. In addition, it was moderated by Jan Rabaey of the University of California at Berkeley.

Rabaey outlined some of the major challenges as the opening for the discussion. Among them:

1. The impact of technology scaling being reduced for new processes;
2. The impact of voltage scaling is reduced as a proportion of new power supply levels;
3. Getting control of the wasted energy in the systems, and
4. Identifying energy efficient design architectures.

At the core of the discussion were two main themes. First, new devices will be at the center. And second, there will need to be new new tools and methods to implement these next-generation designs. The device migration is toward 3D devices and low leakage devices and substrates such as Fully Depleted SOI (FDSOI) and FinFETs. These structures have the ability to provide consistency in performance despite lithographic challenges. Lithography is just one of the many aspects of variability that area plaguing sub-20nm process technology.

The manufacturing challenges for these new devices have yet to be determined, but the solutions to these challenges will help shape the product designs and architectures. Moreover, yield, predictability and power performance will drive the operating power supplies and determine how much power is wasted in the design through heat and inefficiency in current transfer.

As these devices operate in a different voltage and current modes with different sensitivities from standard planar (2D) devices, new models and device-level simulation tools are needed to capture their characteristics. Due to the small geometries and the resulting large density vs. device units scaling, new matrix-solving routines need to be created to solve the equations without causing the tools to slow down or fail to converge to a solution. This is already driving changes in EDA and CAD to support the devices. The capacity, capabilities and throughput of the current EDA tools is not sufficient to be able to address the new 3D device requirements and their associated block and system designs.

One of the major challenges is to address the guard-banding and safety factors in the designs that are wasting power. Current worst-case design optimization wastes operating power by helping to identify corners of the design space that may not be reachable in practicality, but require power to stay away from. The capacity and extent of verification software that can address multiple levels of the design will have to be created. One of the major issues is creating architectural tools that can help do power optimization as a driving design function rather than just as an analysis tool.

Key issues involving these tools is who will solve the fundamental problems—industry or academia—and whether it will become a viable business. For academia to put resources on solving the guard-banding and multi-level design issues it will need funding from the government (NSF) or industry to pay for the student and facilities needed to complete the work. If it is done by industry, companies need to know that when answers are found that customers will buy the products and that they will have some time advantage over competitors. With the scope and breadth of the new tools that are required, and the skyrocketing costs of building chips at these advanced node, the issue of, ‘Will there be enough people who need the results of the effort for the tool development to be a business,’was left open as one of the keys for addressing the next power plateau.