FD-SOI for Near-Threshold-Voltage Design? It’s a Good Knob, Say #55DAC Expert Panelists

That FD-SOI can be a key to achieving near-threshold voltage design was an important point made during a  #55 DAC expert panel. Entitled How Close to Threshold-Voltage Design Can We Go Without Getting our Fingers Burnt? the session was organized by Jan Willis of Calibre Consulting. Turnout was excellent. Btw, Jan (herself an EDA expert) was one of the original advisors in the formation of the SOI Consortium, and while this DAC panel was not meant to be about FD-SOI, it turned out be a focal point.

Near-threshold voltage design* is an especially hot topic for IoT and edge-computing designers, for whom balancing performance, reliability and extremely low power is generally challenge #1. For them, the ability to get chips working at very low voltages translates into battery life savings.

The original goal of the panel was “…to explore how far below nominal voltage we can design, in what applications it makes sense and in what ways it will cost us.” The description in the #55 DAC program noted that “Energy consumption is the driving design parameter for many systems that must meet ‘always-on’ market requirements and in IoT in general. For decades, the semiconductor industry has attempted to leverage the essential principle that lowering voltage is the quickest, biggest way to reduce energy for a SoC. Some today contend sub-threshold voltage design is viable while others argue for near-threshold voltage design as the minimum.”

#55 DAC Expert Panel: How Close to Threshold-Voltage Design Can We Go Without Getting our Fingers Burnt? Left to right: Brian Fuller, Arm (moderator); Scott Hanson, Ambiq Micro; Lauri Koskinen, Minima Processor; Mahbub Rashed, GlobalFoundries; Paul Wells, sureCore. (Organized by Jan Willis of Calibre Consulting)

The panelists included:

  • Scott Hanson – Ambiq Micro
  • Mahbub Rashed – GLOBALFOUNDRIES
  • Lauri Koskinen – Minima Processor
  • Paul Wells – sureCore Ltd., Sheffield

Brian Fuller of Arm served as moderator.

Panel organizer Jan Willis, Calibre Consulting

Following the panel Jan published the following excellent recap on LinkedIn. She graciously agreed for it to be reprinted here in ASN, for which we thank her. So without further ado, read on!

#55DAC Expert Panel on Near-Threshold Voltage Sees Growing Opportunity Despite Challenges

First published on LinkedIn, June 27, 2018 by Jan Willis, Strategic Partnerships & Marketing Executive

Brian Fuller, Arm, skillfully guided a group of experts through the challenges of near-threshold design to conclude that the adoption is going to start gathering pace in a panel session at the 55th DAC in San Francisco on Monday, June 25.

Scott Hanson, CTO of Ambiq Micro, led off by saying the list of what’s not challenging is a much shorter list but that by taking an adaptive approach, they have been successful. It’s required innovating throughout the design process including test where Scott said they had create their own “secret sauce” to make it work. Later on in the panel, Scott described designers in near-threshold as “picojoule fanatics” to overcome the limitations in design tools which are geared towards achieving performance goals.

Lauri Koskinen, CTO of Minima Processor, agreed that adaptivity is key. Minima says it has to be done in situ in the design to make it robust for manufacturing while useful across more than one design. Later in the panel, Lauri indicated that FD-SOI is like having another knob available for optimizing energy in the Minima approach to near-threshold design.

Mahbub Rashed, head of Design and Technology Co-Optimization at GlobalFoundries, highlighted the need for more collaboration between EDA, IP, and foundries to support near-threshold design but noted a lot of progress has been made on FD-SOI processes. Mahbub cited models down to 0.4V for FD-SOI processes are available now and GlobalFoundries is able to guarantee yield.

Paul Wells, CEO of sureCore, validated that sureCore has bench marked their memories on GlobalFoundries FD-SOI with success. He reflected that FD-SOI has rapidly established itself as cost effective for a number of emerging markets. The panel all agreed that achieving quality on the memory at near-threshold voltage was much tougher than for digital IP. [Editor’s note: sureCore‘s CTO wrote an excellent summary of their SRAM IP for FD-SOI in ASN back in 2016 – you can still read it here.]

Paul went on to summarize at the end of the panel that near-threshold voltage is the way of the future and that it’s gathering pace. Mahbub called upon the EDA community to step up to improve the tools for low energy design. Lauri and Scott both summarized that there were drivers emerging that will grow the addressable market for near-threshold voltage design. Lauri pointed to growth coming from the applications that require edge computing which he thinks will require near-threshold voltage design. Scott concluded the panel by pointing out that there’s been a tremendous increase in performance of near-threshold voltage designs which will increase the addressable available market in the future.

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This piece was first published by Jan Willis on LinkedIn, June 27, 2018. Here is the original.

* As explained by Rich Collins of Synopsys in the TechDesign Forum: “Operating at near-threshold or sub-threshold voltages reduces static and dynamic power consumption, at the cost of design complexity. […] A transistor’s threshold voltage (Vth) is the voltage at which the transistor turns on.  Most transistor circuits use a supply voltage substantially greater than the threshold voltage, so that the point at which the transistors turn on is not affected by supply variations or noise. […] In sub-threshold operation, the supply voltage is well below the Vth of the transistors. In this region, the transistors are partially On, but are never fully turned. Near-threshold operation happens between the sub-threshold region and the transistor threshold voltage Vth, or around 400 – 700mV for today’s processes.