Belgian research organisation IMEC has developed a body-area
network transmitter which consumes only 0.5nJ per bit sent.
"The best [similar] commercial devices we have found so far are
one to two orders of magnitude higher per bit," project director
Stephan Donnay told EW.
The device is a prototype for 802.15.4a, a standard for low data
rate communications between networked sensors up to a few metres
apart.
It transmits using pulse-position modulated ultra-wideband (UWB)
encoding, with pulses on-time or slightly delayed to represent
a zero or a one respectively.
Actual transmission power is 50pJ/pulse, and tricky power
limitations for UWB communication between 3.1 and 10.6GHz mean ten
pulses are required to send one bit "but if transmitter and
receiver are on opposite sides of the body, it is possible we will
have to use more than ten pulses per bit", said Donnay.
Transmitting at 10kbit/s, total power consumption should be
5µW.
The figures come from an IMEC-developed mathematical body-area
propagation model, which has been accepted by the IEEE's .4a
standards committee - of which IMEC is a part. "We have done a lot
of work modelling the propagation channel around a body," said
Donnay. "It seems to be in quite good agreement with our
measurements so far, although we have more to do."
The transmitter is made on a completely standard 0.18µm
CMOS logic process, occupying 0.2x0.3mm on its own, or 0.6x0.6mm
including bond pads, decoupling and ESD protection. "Other
transmitters need special components, like step-recovery diodes, or
use analogue options [in their CMOS]," said Donnay, who's chip
needs no external components. "We do nice spectral shaping of
pulses on-chip," he said.
As the physical layer of 802.15.4a is not yet specified, IMEC's
transmitter is flexible and operates between 3GHz and 5GHz, can
generate pulses from 2GHz bandwidth (useful for positioning
applications) to 500MHz bandwidth with various centre frequencies.
A receiver is in development.
IMEC's proposed body-area network is part of its Human++ medical
monitoring programme. Sensors in clothing, on the skin, or
implanted will send bio-data to a central network controller -
likely to be in a phone or PDA, said Donnay.
www.imec.be