Startup Expected to Ship Chips Operating with Sub-Threshold Voltage in 2015

Intel’s Near-Threshold Voltage Technology Will Not Be Alone

by Anton Shilov
09/19/2013 | 11:50 PM

Ambiq Micro, a startup developing ultra-low-power processors and special-purpose circuits, seems to have extremely ambitious plans for chips, that will power the next wave of digital devices, such as wearable electronic gadgets. The company plans to start sampling an ARM-based microcontroller that operates transistors near and below their threshold voltage in 2014 and produce it in volume in 2015.

Ambitious Plans of Ambiq


Ambiq Micro has developed a unique unique circuit designs and system architectures that enable semiconductor products to run at extremely low voltage levels inside the chip, dramatically lowering the power required for chip operation. The external interface for product designers remains the same as today’s traditional semiconductors, so no new design techniques or methods are required. Ambiq Micro products built on its advanced SPOT (subthreshold power optimized technology) design platform are manufactured using a standard CMOS high-volume, low-cost semiconductor process. The fabless semiconductor company is headquartered in Austin, Texas.

“Ambiq 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,” said Scott Hanson, chief technology officer of Ambiq, in an interview with EETimes web-site.

Ambiq Micro’s AM0800 and AM1800 real-time clock (RTC) families are the first products built on the SPOT platform, and they deliver a 7x improvement in energy efficiency over other RTC products.

The SPOT platform uses transistors biased in the subthreshold region of operation to achieve unmatched energy efficiency. Rather than using transistors that are turned all the way “on,” subthreshold circuits use the leakage of “off” transistors to compute in both the digital and analog domains. With most computation handled by leakage current, total system draw on the order of nanoamps is easily achieved, according to the company.

Subthreshold operation has been used sparingly in select markets like wristwatch and RFID chips, but Ambiq Micro’s SPOT represents one the most comprehensive and aggressive demonstration of subthreshold to date. Ambiq Micro’s patented approach to subthreshold was developed over an 8 year research effort by University of Michigan engineers and Ambiq Micro engineers.

Specs of the SPOT

Digital circuits implemented with the SPOT are designed to run at supply voltages at or below the transistor’s threshold voltage. A superthreshold digital circuit in a typical manufacturing process operates with a 1.8V supply voltage and a switching threshold of approximately 0.9V. In the same process, a subthreshold digital circuit may operate with a supply voltage near 0.5V and a switching threshold near 0.25V. With such a small voltage swing, considerably less charge (and thus energy) is used to run computations. Operation at such low voltages is complicated by susceptibility to noise, high sensitivity to temperature, and a variety of challenges. In developing its SPOT platform, Ambiq Micro has addressed all of these challenges by redesigning every digital circuit in the chip, from standard cell building blocks to internal voltage regulators.

SPOT-enabled analog circuits typically run at higher supply voltages than their SPOT-enabled digital counterparts but are biased in the subthreshold regime. The transistor current-voltage curve shows nearly all conventional analog circuits use superthreshold bias currents on the order of 1µA. Analog circuits designed with the SPOT platform use subthreshold bias currents on the order of 0.1nA. As with digital design, operation in this regime is complicated by several challenges including high sensitivity to temperature/voltage fluctuations and manufacturing variations. The SPOT uses proprietary analog building block circuits that are redesigned exclusively for subthreshold operation and are resistant to the aforementioned fluctuations and variations.