http://www.c2s2.org
www.c2s2.org
9 mm
Wireless Communication Systems for Bio-sensors
H. Miranda ([email protected]) and Prof. T. Meng
Department of Electrical Engineering, Stanford University
Abstract
Technical focus Sophisticated implantable medical devices enable numerous important diagnostic and therapeutic
applications. Among these, a class of devices that require large amounts of data processing are
emerging, such as neural prosthetics and retina implants. For these devices to be clinically viable
the current transcutaneous wire connections, which are prime source of failure and infection, need
to be eliminated. Developing very low-power, high-bandwidth wireless data and power links to
replace the wired connections for micro-scale implanted medical devices is a key research
challenge, and the main focus of the this task.
Results Two major steps were given to achieve the task goal. The HermesD discrete transmitter was
successfully tested on an actual rhesus monkey. This system supports the simultaneous
transmission of 32 channels of broadband data at 30 ksps, using FSK modulation on a 3.95 GHz
carrier, with a link range of over 10 m. More recently, the IC design of the future HermesE version
was concluded (chip in manufacturing). This transmitter is a very low-power
(< 1 mW) and low size (8x16x2 mm3) UWB transmitter capable of transmitting 96 channels of
neural data.
Hermes Project
Electrode
array
implant
Neural prosthesis research: high data-rate biological application Neural signals are measured using arrays
of electrodes implanted in various brain regions(96 electrodes)
Electrode signals are transmitted and/or stored
Neural spike times are extracted for each neuron (spike sorting)
Desired arm movement is estimated
Control signals are generated to guide prostheses (robotic arm for instance)
Hermes B and C: Current versions
Two channels recorded out of the
96 available
Battery and memory autonomies
are both limited to 18 h
Data rate is 360 kbit/s/channel 30 ksamples/s per channel
10 bits per sample
Wireless capability introduced in
HermesC 900 MHz ISM band, FSK Modulation
One channel transmitted at
16 ksamples/s, 10 bit/sample
Max. communication range: 4 m
Power consumption: 50 mW
digital board
analog board
battery 1 battery 2
chronic electrode array
silicone elastomer
methyl methacrylate
preclude
white matter
gray matter
dura matter
bone
screw gnd
screw
protective shield
gasket
screw
HermesD: High-rate, multi-channel transmitter
Supports the transmission of 32
channels of broadband data 30 ksamples/s
12 bits/sample
Operating frequency of 3.95 GHz,
FSK Modulation, 24 Mbit/s
Reconfigurable digital control
and data framing for easy
modification (such as changing
the nr. of chnnels)
Communication range: > 10 m
Total power: 150 mW 2 days of operation time
analog / digital / transmitter board
battery 1 battery 2
chronic electrode array
silicone elastomer
methyl methacrylate
preclude
white matter
gray matter
dura matter
bone
screw gnd
screw
protective shield
gasket
screw
3.95 GHz
patch antenna
HermesD recording (one-channel)
Next generation: HermesE, a multi-channel, very low-power transmitter
Evolution towards a fully implantable solution Analog/digital IC + Transmitter/antenna IC on a
20 x 20 mm board
chronic electrode
array
silicone elastomer
methyl methacrylate
preclude
white matter
gray matter
dura matter
bone
Analog / digital IC
UWB Tx IC / antenna
Implanted
electrode
array
Amplifier
ADCs
Multiplexers
UWB processor
and
transmitter
Implanted
antenna
96 channels
300 kS/s/ch
< 5 mW < 1 mW
40 Mbit/s
Implanted electrode
Array (4x4x1 mm)
ProgProg
Continuous transmission of all 96 channels inbroadband mode Required bit rate: 40 Mbit/s
Total expected powerconsumption: Analog + ADC: < 5 mW
Transmitter: < 1 mw
UWB transmitter design goals for HermesE
Pulse based UWB
Frequency range: 4 – 8 GHz
(3.1 – 10.6 GHz UWB band)
Data rates in excess of 40 Mbit/s
DC Power < 1mW
Range to cover > 3 m
Programmable pulse envelope and duration
(spectrum control)
Good transmitter energy efficiency (>20%)
HermesE UWB transmitter UWB architecture
All transmitter parameters
programmable: Pulse center frequency (Fpulse) by controlling the
cell delay (delay 1 — delay n control bits)
Pulse BW set by the number of stages (BW)
Pulse shape controlled by the antenna driver
transistor size (amp 1 — amp n control bits)
Pulse phase scrambler “whitens”
the RF spectrum
Ltune/Ctune resonant at Fo
single
pulse
cell 1
single
pulse
cell 2
single
pulse
Cell n
OOK
modulator
Vant
Ltune
Ctune
data
clock
Pulse delay control bits
R
antenna
Ccamp 1 amp 2 amp n
delay 1
Pulse amplitude control bits
delay 2 delay n
Phase
scrambler
Simulation Results: pulse waveforms
Design example: Fcenter = 4 GHz
BW = 1 GHz, Ncells = 8
Vdd = 1.0 V, Vant = 0.5 V
Rectangular and Gaussian pulses
Energy performance
(rectangular pulse): DC energy/pulse: 5.5 pJ,
RF energy/pulse: 1.7 pJ
Modulator / Pulse generator energy: 0.6 pJ
Avg. DC power @ 40 Mbit/s, OOK modulation: 110 W
RF pulse peak power: 850 μW
Driver weight vector: W = [7 7 7 7 7 7 7 7]
Driver weight vector: W = [1 2 5 7 7 5 2 1]
HermesE efficiency performance
Energy efficiency vs antenna driver voltage Rectangular pulse
10 dB
1 GHz
Spectrum utilization efficiency The phase scrambler enables a 10 dB
increase in output power for the same spectral mask compliance
Scrambler off Scrambler on
HermesE chip layout
OOK
modulator
Phase
scrambler
Configuration
registers
Pulse
generator Antenna driver
Single pulse cell (10 cells)
Output capacitor (Ctune)
65 nm 1P9M 1.0 V process
Die area: 1.0 x 0.7 mm2
HermesE Test board
Chip-on-board
assembly
Test board includes
commercial UWB
antenna
Alternative antenna: L-shapped circular disk monopole (LCDM) antenna Lower profile than the standard
CDM while maintaining UWB characteristics
Semi-hemispherical radiation pattern
Radiantion pattern at 6 GHz Return loss
Summary
2008-2009 contributions Development, implementation and test of a 24 Mbit/s wireless transmitter to support 32
channels of broadband data for the Hermes system.
IC implementation and simulation of a very low-power and high-rate integrated UWB
transmitter for neuro-implants (HermesE).
HermesE antenna simulations and lab measurements
Related references H. Miranda, V. Gilja, C. Chestek, T. Meng, K. Shenoy, “A high-rate long-range wireless
transmission system for multichannel neural recording applications”, International Symposium
on Circuits And Systems, Taipei, Taiwan.
Chestek, C.A. Gilja, V. Nuyujukian, P. Ryu, S.I. Shenoy, K.V. Kier, R.J., “HermesC: RF
wireless low-power neural recording system for freely behaving primates”, International
Symposium on Circuits and Systems - ISCAS 2008, Seatle, USA, 2008.
G. Santhanam, M. Linderman, V. Gilja, A. Afshar, S. Ryu, T. Meng, K. Shenoy, “HermesB: A
Continuous Neural Recording System for Freely Behaving Primates”, IEEE Transactions on
Biomedical Engineering, Vol. 54, No. 11, Nov 2007
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