An ARM core operating down at near or sub-threshold is likely to drive greater revenue at the company, but ARM CTO Mike Muller has recently expressed some doubts about sub-threshold operation while announcing his company is developing a core optimized for near-threshold operation in energy-harvest applications. (See ARM Preps Near-Threshold Processor for IoT.)
"It is a spectrum of opportunity. In our approach there is both near- and sub-threshold operation. They are not that different. Near or sub you still have to overhaul the design process," said Hanson. "I agree with Mike [Muller] that near is easier to commercialize but we like difficult. It gives us more chance to create value."
Hanson said Ambiq is producing its real-time clock chips using a standard CMOS process at foundry Taiwan Semiconductor Manufacturing Co. Ltd. Although Hanson declined to nominate the geometry of the processes the company uses, he acknowledged that by operating the circuits outside the conventional parameters of the manufacturing process, Ambiq takes on extra responsibilities in terms of yield and achieving specification:
There is additional risk that we take on but we have ways of mitigating that. We don't tend to use leading-edge processes. There is an advantage for a startup to stay away from where the mask sets cost millions of dollars.
With a focus on mixed-signal ICs, Ambiq is unlikely to migrate down to 20-nm any time soon, but Hanson made the point that sub-threshold design could benefit from all of the alternative transistor configurations being introduced at the leading-edge; FinFET, FDSOI, and SuVolta's deeply depleted channel (DDC) technology. "If one of those were applied at 65-nm it could be interesting," Hanson said.
The arguments persuaded Austin Ventures to lead the latest funding round, which has brought the total invested in the company to about $21 million. "Austin Ventures expects Ambiq Micro products to have a major impact in many high-growth applications. Long life will be the driving factor behind consumer acceptance of new networked, battery-operated devices," said Clark Jernigan, venture partner, Austin Ventures, in a press release.