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Ambiq to sample out sub-threshold ARM MCUs by 2014

Posted: 23 Sep 2013 ?? ?Print Version ?Bookmark and Share

Keywords:Ambiq Micro? MCUs? wearable devices? portable medical equipment?

Ambiq Micro, a fabless start-up, is on track to start sampling an ARM based microcontroller operating on transistors near and below their threshold voltage in 2014. In a recent interview, Ambiq's chief technology officer Scott Hanson stated that volume production of sub-threshold microcontrollers is then expected in 2015.

Based in Austin, Texas, Ambiq also announced it has raised $10 million in a Series B funding round led by Austin Ventures and with participation of the company's existing shareholders, including ARM Holdings plc, which will help fund the development of MCU chips and expand the company's market presence.

Hanson said the company is designing mixed-signal devices based on the Cortex-M0+ core from ARM, but rather than being general-purpose MCUs, these MCUs are tailored for emerging applications where power consumption is critical. Typical applications would include: wearable devices, smartcards, wireless sensors, and portable medical equipment, he mentioned.

While sub-threshold operation limits the attainable clock frequency and performance of digital circuits when compared to conventional operation, the technique reduces significantly the power consumption of such circuits.

The company describes its sub-threshold power-optimised technology (SPOT) process as turning "microamps into nanoamps." The threshold where a transistor can be turned on and significant current flows is in the region of 0.3 to 0.6V, depending on the manufacturing process, but around the threshold, the device characteristics have exponential dependencies on voltages and temperature making design difficult.

Ambiq was formed in 2010 to commercialise sub-threshold research carried out at the University of Michigan. However, the company's first products were the AM08XX and AM18XX real-time clock (RTC) chips, which the company claimed were the world's lowest power RTC chips due to their use of the SPOT process.

"They are seven times more power efficient than the nearest competitors and producing attractive revenue right now. They are a big driver to getting us cash-flow positive in the very near future," Hanson said.

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 optimised for near-threshold operation in energy-harvest applications.

"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 commercialise 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 start-up to stay away from where the mask sets cost millions of dollars," he added.

With a focus on mixed-signal ICs, Ambiq is unlikely to migrate down to 20nm 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 65nm 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.

- Peter Clarke
??EE Times

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