http://www.c2s2.org

www.c2s2.org

9 mm

Wireless Communication Systems for Bio-sensors

H. Miranda (hmiranda@stanford.edu) 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

μ