Transceiver has designs on radio under the skin

A novel intelligent radio transceiver architecture introduces a new level of power economy and performance for in-body medical diagnostic and therapeutic applications.

Cambridge Consultants has designed an intelligent radio transceiver architecture claimed to introduce a new level of power economy and performance for in-body medical diagnostic and therapeutic applications.

The design is intended for implementation on system-on-chip (SoC) solutions and provides a control and communications platform suitable for implantable medical devices - a market currently growing at double-digit rates.

The device will operate in the Medical Implant Communications Service (MICS) frequencies - the medical band now emerging as a global standard.

A key attribute of Cambridge Consultants' design is exceptional power economy, and the architecture would consume an average current of less than 1uA, and less than 1.7mA peak, for a 0.05% duty-cycle, 400Kbit/s bidirectional communications application.

This would provide more than 10 years of activity from a lithium cell in a typical pacemaker application, for example.

However, flexibility built into the radio design also allows the chip to be used for other systems with short-term high-datarate communications requirements - such as swallowable video imaging.

"Advances in electronics technology are enabling a host of new implantable applications, and this design draws on three of those trends: ultralow power consumption provided by cost effective CMOS/BiCMOS processes, enhanced radio performance through lean microcontroller and low-power DSP digital cores, and extreme miniaturisation enabled by system-on-chip integration capabilities", says Richard Traherne, Head of Cambridge Consultants' Wireless Business Unit.

"Combined with the opportunities offered by the MICS frequency allocation - which is emerging as a worldwide standard endorsed by the FCC and ETSI - we see great demand for an optimised single-chip wireless platform that delivers the economy required for mass-volume medical applications".

The new implantable transceiver design, called SubQore, leverages Cambridge Consultants' portfolio of field-proven intellectual property for ultra-low-power radio, as well as the consultancy's lean RISC processor core, XAP.

Extreme attention to power economy has been applied throughout the design, both to consumption in the transceiver architecture, as well as the power-saving algorithms that are employed to wake up and control the device.

Although the range of implantable medical applications is expanding exponentially, each application is different and requires a particular mix of control, monitoring and communications facilities - and Cambridge Consultants expects to fine-tune the IC core for individual applications.

SubQore's architecture reflects this diversity of potential use.

In its basic form, SubQore's radio employs digital phase-shift keying (PSK) data modulation - a highly power-efficient scheme.

However, the hardware that controls modulation has been designed to provide a degree of DSP (digital signal processor) flexibility, to support the use of higher-efficiency schemes for more demanding applications such as video transfer.

The XAP microcontroller core provides similar flexibility, and can be equipped with a range of digital and analogue I/O - and memory sizes - to suit the application.

The SubQore radio operates in the 402-405MHz MICS (Medical Implant Communications Service) frequency band - compatible with new FCC and ETSI standards - and offers a communications range of 2m when implanted under the skin.

The only other use of this band is for meteorological equipment, minimising the potential for interference and providing an excellent platform for economy of scale through standardisation.

The low-IF radio receiver architecture employed in this design, adapted from high-efficiency pager technology, offers lower power consumption and better immunity to interference than direct conversion receivers.

SubQore is also optimised for physical compactness and requires just 10 components, enabling subcutaneous radios to be the size of a button using system-on-chip technology.

Among the applications that Cambridge Consultants sees for high-performance/long-lifecycle MICS cores are implantable pacemakers, defibrillators, remote telemonitors, orthopaedic devices, pump controllers, nerve stimulators and swallowable imaging and diagnostic systems.

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