Currently in its infancy, the short-range RF sector is set to boom and the catalyst for this expansion will be ultra low-power technology, as Thomas Embla Bonnerud, Product Manager at Nordic Semiconductor explores

Ultra low power (ULP) wireless applications are set to increase dramatically. According to analysts ABI Research, for example, the wireless sensor network (WSN) chips market grew by 300 percent in 2010 and they also forecast that no less than 467 million healthcare and personal fitness devices, using ULP chips will ship in 2016.

But what are these chips and how do they operate? Unlike other wireless technologies such as Wi-Fi and Bluetooth wireless technology, ULP transceivers are designed to run from batteries of modest capacity such as coin cells (for example, the CR2032 or CR2025 type). Typical applications are based on compact sensors, for example a heart rate monitor (HRM).

To track the pulse and display the information on a wristwatch only requires the transceiver in the HRM to send small quantities of data (typically a few bits) infrequently (i.e. once every few seconds to a few times per second at most).

Duty cycles of 0.25 percent are common with the transceiver spending much of the time in a low energy consumption sleep state.

The duty cycle is minimised because the transceiver wakes up quickly, sends a relatively high-bandwidth ‘burst’ of data (at a rate of up to one or two Mbps), before immediately returning to sleep.

The combination of low duty cycle and the great efficiency of today’s ­silicon radios is the secret behind the technology’s ULP performance.

During the short period of activity, the transceivers operate at peak ­currents of just tens of milliamps. Thereafter the chip returns to sleep state, drawing just nanoamps.

Because transmit/receive time is so short, the average current consumption over the long term is just tens of microamps.

In simple terms, wireless connectivity requires a radio, software code to control communication (‘protocol’) and an application processor (with its own code, that supervises the specific application).

How these elements are implemented affects the efficiency, size and cost of the wireless system.

Until recently, the sector was dominated by proprietary solutions (i.e. one that uses technology owned by a single company). This was primarily because the semiconductor vendors were able to optimise the silicon and protocol without the encumbrance of additional overheads required for the assured interoperability, typical of a standards-based solution.

The result is a more efficient ­solution with lower power consumption and reduced cost – the two critical ­factors for companies searching for the best ULP wireless solution.

So-called ‘ultra-low-power’ wireless technologies such as ZigBee, while offering impressive performance, couldn’t compete with the power ­consumption of the best of the proprietary offerings.

The demand for interoperability

As ULP wireless has diversified into more applications, the lack of interoperability has started to become a ­problem for some OEMs.

The success of Bluetooth wireless technology has demonstrated the huge benefits of establishing a wireless ‘ecosystem’ where products from different manufacturers can seamlessly connect.

However, the Holy Grail for interoperable ULP wireless technology promoters is to emulate the success that Bluetooth wireless technology has had in the low power RF sector.

That ambition is now set to become reality because the custodian of Bluetooth wireless technology, the Bluetooth Special Interest Group (SIG), has now ratified a version that can operate from coin cell batteries.

So-called Bluetooth low energy (a hallmark feature of the latest release of Bluetooth wireless technology, Version 4.0) has been designed to allow sensors and other peripheral devices to communicate with each other and products such as the next generation of mobile phones.

Semiconductor vendors are now shipping Bluetooth low energy chips. For its part, Nordic – which played a significant role in the development of the specification, donating its extensive ULP wireless design heritage to the technology – has released the first in its µBlue Series of Bluetooth low energy chips.

The chip is a complete Bluetooth low energy solution in a 32-pin 5 by 5mm QFN package incorporating a fully embedded radio, link controller, and host subsystem. The device is suitable for watches, sensors and remote controls among other applications. Casio’s recently released G-SHOCK Bluetooth Low Energy Watch uses this chip (pictured).

The Bluetooth SIG’s stated intention is to release Profiles for Bluetooth low energy, including Personal User Interface Devices (PUID) (such as watches), Remote Control, Proximity Alarm, Battery Status and Heart Rate, in the next several months. Other health and fitness monitoring profiles such as blood-glucose and pressure, cycle cadence and cycle crank power will follow.

Bluetooth v4.0 chips are also becoming available. Devices such as mobile phones should start to incorporate these chips – as a replacement for the current generation of Bluetooth wireless technology -in the second half of 2011. Once that happens, the full potential of this exciting new technology will start to be realised because the ULP wireless-powered devices will be able to link directly with the huge Bluetooth ecosystem.

As designers now have an inexpensive way to add an interoperable wireless link to anything that’s battery powered, even devices with the smallest batteries, the application potential is vast.