Cambridge Consultants has designed an intelligent radio transceiver architecture 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. The device will operate in the medical implant communications service (MICS) frequencies—the medical band now emerging as a global standard.

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A key attribute of Cambridge Consultants' design is power economy. The architecture would consume an average current of less than 1 µA and less than 1.7 mA peak, for a 0.05% duty-cycle, 400 Kbps bi-directional communications application. Consequently, it would provide more than 10 years of activity from a lithium cell in a typical pacemaker application. However, flexibility built into the radio design also allows the chip to be used for other systems with short-term high data rate communications requirements—such as swallowable video imaging.

The new implantable transceiver design, called SubQore, leverages Cambridge Consultants' portfolio of field-proven intellectual property for ultralow-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 power-efficient scheme. However, the hardware that controls modulation has been designed to provide a degree of digital signal processor 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 analog I/O—and memory sizes—to suit the application.

The SubQore radio operates in the 402-405 MHz MICS frequency band—compatible with new FCC and ETSI standards—and offers a communications range of 6 feet (2 meters) when implanted under the skin. The only other use of this band is for meteorological equipment, minimizing the potential for interference and providing an excellent platform for economy of scale through standardization.

The low-IF (intermediate frequency) 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 optimized 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-life-cycle MICS cores are implantable pacemakers, defibrillators, remote telemonitors, orthopaedic devices, pump controllers, nerve stimulators and swallowable imaging and diagnostic systems.