Toshiba Develops Extremely Low-Power 2.4 GHz VCO Utilizing Dynamic Supply Voltage Control Technique

Toshiba Corporation (TOKYO:6502) today announced that it has developed an extremely low-power 2.4 GHz Voltage Controlled Oscillator (VCO) for low-power wireless systems, such as Bluetooth^® Low Energy (BLE). Low-voltage operation below the threshold voltage of the transistor is achieved by combining the features of a class-D VCO and dynamic control technique of the supply voltage. The power consumption of the VCO is reduced to one-fifth to one-tenth compared to the conventional one. Toshiba presented the VCO in European Solid-State Circuits Conference (ESSCIRC) in Venice, Italy, on September 24^th 2014.

Recently, applications of wireless communication have widened to include sport, fitness, healthcare, watches and more. As these applications often assume long-life operation with low-capacity batteries, such as a coin cell battery and energy harvester, extremely low-power wireless IC is required. This has spurred research into low-power wireless ICs and individual building blocks.

Among building blocks, reducing VCO power consumption is particularly challenging, as superior noise performance depends on high power consumption. Many techniques for low-noise and low-power consumption of VCO have been researched, mainly focused on reducing current consumption. However, for extremely low-power, reduction in the voltage domain is necessary.

Toshiba has applied class-D VCO developed with advanced CMOS technology, which use transistors as switches (not as transconductors, like conventional VCOs). Although the class-D VCO can achieve superior noise performance at low supply voltage, the supply voltage also has to be as low as possible for extremely low-power.

An extremely low-power VCO has been developed with a dynamic supply voltage control technique that uses a Low-Drop Out (LDO) circuit as the dynamic supply voltage controller. At start-up of the VCO, the supply voltage is boosted to ensure fast, reliable start-up. In the steady-state after start-up, the supply voltage is controlled below the threshold voltage, which keeps the oscillation even in the supply voltage below the threshold voltage of the transistor, as a characteristic of the class-D VCO is an oscillation amplitude about three times higher than the supply voltage. The extremely low-voltage operation results in the low-power consumption by the VCO.

The test chip is fabricated in 28nm CMOS technology with high threshold voltage. While high threshold voltage can reduce leakage current in sleep-mode, it increases power consumption in conventional class-D VCOs, because higher supply voltage is required. However, since the proposed VCO can oscillate at lower voltage than the threshold voltage, low-power oscillation can be available even with high threshold voltage. Extremely low-power consumption of only 171uW is achieved, along with phase noise performance required for low-power wireless systems.

Dynamic supply voltage control can solve the trade-off between leakage current in sleep-mode and active power consumption in active-mode. Furthermore more efficient wireless system can be made available when this low-voltage VCO is used with energy sources such as a DC/DC converter and an energy harvester.

This VCO can operate in extremely low-power consumption with advanced CMOS technology. Moving forward, Toshiba will next advance power reduction in total wireless systems as well as VCO building blocks, aiming to realize an extreme low-power wireless IC in the next three years.

* Bluetooth is a registered trademark owned by Bluetooth SIG, Inc. and any use of such mark by Toshiba is under license.

About Toshiba

Toshiba Corporation, a Fortune 500 company, channels world-class capabilities in advanced electronic and electrical product and systems into five strategic business domains: Energy & Infrastructure, Community Solutions, Healthcare Systems & Services, Electronic Devices & Components, and Lifestyles Products & Services. Guided by the principles of The Basic Commitment of the Toshiba Group, "Committed to People, Committed to the Future”, Toshiba promotes global operations towards securing "Growth Through Creativity and Innovation”, and is contributing to the achievement of a world in which people everywhere live in safe, secure and comfortable society.

Founded in Tokyo in 1875, today’s Toshiba is at the heart of a global network of over 590 consolidated companies employing over 200,000 people worldwide, with annual sales surpassing 6.5 trillion yen (US$63 billion).
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