New Breakthrough Wearable Biosensor Technology Featuring Industry-Low Power Consumption*

*ROHM November 2014 study

ROHM, in collaboration with Professor Yoshimoto Masahiko of the Department of Information Science at the Kobe University Graduate School of System Informatics, has successfully developed the world’s smallest ultra-low-power technology optimized for next-generation wearable biosensors under the ‘Development of Infrastructure for Normally-Off Computing Technology’ project conducted by NEDO.

This technology utilizes non-volatile memory in order to suppress standby power generation by enabling the power supply to be turned OFF when no processing/operation is required. Normally OFF operation is achieved by turning the power ON immediately when needed, minimizing power consumption.

Wearable biosensors adopting this method can easily determine the heart rate by detecting small potential differences on the surface of the skin (EKC/ECG waveforms) using only 6uA of current– the lowest on the market. In addition, information from other digital sensors such as accelerometers can be acquired, calculated, and recorded. Communications functions are also built in that make biosensor control possible via smartphone or tablet and to facilitate data input/output. Furthermore, only 38uA is required for all operations – 5x lower than conventional products, resulting in the lowest power consumption on the market.

Joint development of wearable biosensors based on customer requirements has already begun, including battery-free designs utilizing ROHM’s piezoelectric MEMS technology that consume 10 times less power, and results announced at the international IEEE/CAS-EMB BioCAS 2014 conference (Oct. 22-24 in Switzerland) as well as at ASSCC (Nov. 10-12 in Taiwan).

In virtually all types of portable electronic devices, including smartphones and wearable tech, designers have been trying to minimize power consumption in order to maximize battery life. In wearable devices in particular where the user may forget he/she is wearing the product, reducing the battery size while providing long-term operation is essential.

In response to this need, NEDO initiated the ‘Development Infrastructure for Normally-Off Computing Technology’ project in 2011 in order to achieve unprecedented energy savings by using non-volatile devices that retain data even when the power is cut off. NEDO also performs R&D on other projects with support from a number of companies and universities.

Among these, ROHM and Kobe University’s Yoshimoto Laboratory have taken full advantage of non-volatile logic technology and ROHM’s market-proven non-volatile memory (FeRAM) to establish groundbreaking proprietary normally-OFF technology, and are currently adopting this for wearable biosensors utilizing ROHM’s 0.13um CMOS processes.

Key Features

ROHM implemented 3 proprietary power-saving measures to achieve the lowest power consumption in the industry.

① Reduce the power consumption of heart rate acquisition block by 20x

A new heart rate waveform algorithm featuring excellent noise immunity is incorporated into the power-hungry heart rate acquisition analog block, and some components were replaced with normally-off digital processing, reducing power consumption by 20 times.

②Decrease the average power consumption of the memory block to less than 1/10^th conventional levels

Developing and adopting non-volatile RAM based on FeRAM have made it possible to significantly reduce standby current required for operation.

③ Cut the power consumption of the logic block by more than half

Enabling normally-off operation by incorporating non-volatile logic within the digital circuit block (including the ARM Cortex-M0) results in significantly lower power consumption.

Applications

・ Wearable biosensors

・ Monitoring sensors for bridges and other structures

・ Sensors for agricultural use

・ Power supply ICs for energy harvesting devices

・ Low power ICs with non-volatile functionality (i.e. parameter adjustment)

Terminology

・ Normally-Off

Refers to systems that actively turn off the power to all blocks except for those that require operation. Non-volatile memory is often incorporated to retain data and system information even during power off.

And although similar technologies exist, such as ‘intermittent operation’, in these types of systems the main core elements need to be continuously powered in order to achieve successful performance, resulting in much higher power consumption.

・ Non-Volatile Devices

Refers to devices that retain data and status conditions even when the power is off. Examples of non-volatile memory include flash, FeRAM, and EEPROM – in contrast to conventional memory such as DRAM and SRAM.

・BioCAS (Biomedical Circuits and Systems Conference)

An IEEE-approved international conference where announcements are made and opinions exchanged regarding technologies and innovations in the advanced biological and medical fields. 2014 marks the 10^th anniversary of the conference.

・ASSCC (Asian Solid-State Circuits Conference)

An IEEE-approved conference held in Asia, where the latest products and circuit technologies in the semiconductor industry are announced and opinions exchanged.