Not millimetre wave but millimetre-scale radio

David Blaauw and colleagues from the University of Michigan – a team that has done a lot of work in near-threshold circuitry and other low-power techniques – have written about their programme to develop radios for tiny, implantable computers at EETimes.

The problem for radio circuitry in systems that need to be powered by a small cell for years on end is, as they describe: 

“Typical wireless radios have high peak power consumption, which cannot be sustained by micro batteries with peak currents of 10μA. 

“They also use large off-chip antennas and precision crystal frequency references, which do not scale to volumes below 1mm³, or integrate with CMOS processes. In order to realize true mm-scale wireless systems, we are developing fully-integrated 1mm³ radios and antennas with strict limits on peak-power and energy/bit, and that eliminate the need for an external crystal reference.”

The Michigan researchers describe how they went about designing a radio for an intraocular pressure monitor for monitoring the progress and treatment of glaucoma. They used an array of capacitors spread across the die to supply power the transmitter when sending a bit of data:

“Upon transmission of every bit, the oscillator is turned off to give the capacitors enough time to recharge. This way, we overcame the peak current issue by trading off bitrate, which is not limiting in our system.”

They detail other techniques such as the use of dual-resonator tank circuits to relax phase-noise constraints and digitally tunable references to remove the need to use power-hungry analogue voltage reference circuits. The work was first described at the recent International Solid State Circuits Conference (ISSCC): the papers for this year’s conference are not yet online.

Posted by Chris Edwards

The Low-Power Design Blog is sponsored by Mentor Graphics. The company has focused years of R&D on low-power design techniques and is glad to support a resource that highlights creative methods for reducing the power consumption of electronic systems.