Introduction Inductive link - Polytechnique Montréal · PDF file• Introduction...

1

17 & 24 novembre 2014

GBM8320 - Dispositifs Médicaux Intelligents 2

•  Introduction •  Power and data links

•  Inductive link •  Choice of carrier frequency •  Transmitted power limits •  Inductive system modeling •  Conditioning and calibration techniques

•  Discrete and integrated circuitries •  Power transfer •  Up and downlinks data transmission •  Modulation and demodulation

•  Batteries •  Miniature, rechargeable, etc.

2


Power and Data Link : Typical architecture

Modulator

Demodu- lator

External controller

Data processing

Receiver

AC/DC Supply

Back telemetry

Measure &

digitize MUX

DeMUX

Main Controller

Stimuli generator

Current sources

Test stimuli

Electrodes Skin


Analog toDigital

Converter

Pressure

pH

Temperature

NO or O2

Concentration

ElectricalImpedance

PowerRegulation

DigitalControl

Unit

RFTransmitter/

Receiver

Modulator&

Demodulator

Implantable Wireless Sensor Microsystem

MUX

... Data transmitted to a Base Station

outside of the body

Power and Data Link : Multisensing devices

3


Embedded medical devices : Power sources

•  Energy scavenging, power harvesting : •  MEMS, Vibration, Thermoelectric, Piezoelectric, etc •  Fuel Cells (electrochemical, reaction of Hydrogen/Oxygen) •  Bioreceptors (Glucose, Enzyme, Neural cells, etc). •  Booster using Inductive Ring Oscillator •  Radio signals.

•  Inductive powering •  Transcutaneous RF: no internal power source

•  Primary: Wearable systems including battery •  Secondary: Implants w/ rechargeable battery if needed.

1V, 1uA, from 50 mV


Transcutaneous link : RF Inductive Powering •  Inductive powering is a common method for providing energy to

implantable wireless devices. •  For systems having large power consumption or requiring long lifetime

•  External coil is usually driven by a transmitter operating at a suitable frequency to provide adequate power to the device.

VDC

LOAD

* *R1

MC1

L1 L2 C2Vs

C3

inductive link rectifier linear regulator

~

Vrec VoltageRegulator

R2

4


Inductive Powering : Choice of Carrier Frequency

•  More power loss in the power transmission and conditioning circuitry at higher frequency

•  For 1MHz < fc < 20MHz, average density of electromagnetic power absorption in tissue increases as f2

•  Carrier Frequency fc ~ Penetration depth D

•  Two major limits: 1) Coil self-resonance frequency, 2) EM energy absorption in tissue

•  When EM waves propagate through body tissues (skin, bone, fat, body fluid) to reach the receiving antenna, they are attenuated along the way.

•  d is tissue thickness. •  D is tissue skin depth.

K = 1 - exp (- 2d / �)


Inductive Powering : Transmitted Power Limits

•  IEEE has recommended a standard for safety with respect to RF exposure.

•  For biomedical implantable systems, RF powering occurs within a controlled environment.

2 7.6 12.5 200 Maximum Power Density (W/Cm2)

10 5.12 4 1 Frequency (MHz)

•  If fc equals 5.12MHz and the transmitter coil has a diameter of 10mm, the transmitted power has to be less than 6W.

•  The received power is then determined based upon the inductive link configuration and telemetry distance.

5


Inductive Powering : Coils coupling factor

•  External coil is driven by an RF amplifier at a suitable frequency.

•  Secondary coil captures a portion of the EM field, inducing a current. •  Captured energy by the secondary coil depends on coupling factor, K.

•  0 < K < 1; dimensionless; Typical values are 0.01-0.1. VDC

LOAD

* *R1

MC1

L1 L2 C2Vs

C3


~


R2

322

22

)( readerreaderimplant

readerimplant

rxrr

rrK

+=

•  K is an important factor in the operation of any inductively coupled system

•  ri & rr are the radii of the two coils with x being the distance between them.

•  Assumptions: coils are parallel and center-aligned with only air between them.


Model of the inductive link front-end. •  R1 = parasitic resistance; C1 = tuning capacitance; and RL = system load.

•  L1 and L2 represent a weakly coupled transformer.

VL

1

2/

LLkn = /

12 n

ii =

i2

V2

VL =V2

1+ (R1 + jwL2 ).( 1RL

+ jwC1)

V2 = jwk 2 L2 (

i1n/ ) = jwk L1L2 .i1

VL =wk L1L2 i1

(wL2

RL

+ wR1C1)2 + (1− w2 L2C1 +R1

RL

)2

= Aki1

6


RF Inductive Powering : System View

4MHz 1k 1 330pF 3.7 uH 43.5 uH

f RL R1 C1 L2 L1

VL = 1270.k.i1

VL =wk L1L2 .i1

(wL2

RL

+ wR1C1)2 + (1− w2 L2C1 +R1

RL

)2

= Aki1

•  At a fixed distance, the voltage on the implanted coil can be adjusted by changing the current in the primary coil.

•  We require VL to be within a certain range. •  k is a factor of the distance between the coils. •  Example:


RF Inductive Powering : Conditioning Circuitry •  But, this is clearly not

enough!

•  Received voltage across the secondary coil is a sinusoidal voltage with little or zero dc value.

•  Power conditioning circuitry such as integrated voltage rectifiers and regulators are also needed to generate a clean dc power supply.

VDC

LOAD

* *R1

MC1

L1 L2 C2Vs

C3


~


R2

Primary resonant

signal

Secondary induced signal

Rectified voltage (half

rectifier)

Regulated voltage supply

7


VDC

LOAD

* *R1

MC1

L1 L2 C2Vs

C3


~


R2

rflink=

Zr

Z1

=k 2 R2C2

R1C1 + k 2 R2C2 rectifier=

Vrect

Vrect + 2Vdiode regulator≈

VDC

Vrect

� � �


Inductive link : Power transfer efficiency (Cont’d)

ηtotal =

12

k 2VDC

2 C2

R1C1Pload +12

k 2C2 (Vrect + 2Vdiode ) ⋅VDC

=

12

k 2VDC

2

R1Pload +12

k 2 (Vrect + 2Vdiode ) ⋅VDC

s

srect

VRkR

kR

VCRkCRRCCk

V

22

1

2

222

11

221

+

=

+⋅

=

External Controller Implant

Data Modulator PA

Battery

Shunt regulator

Rectifier

L2 C2

C1

L1 To/From other parts

Skin

8


+-

* *

R1

M

C1

L1 L2 C2R2b

Vs

Data Encoderdata direction

ASKDemodulator

Data Out

Data InImplantExternal

R2a

External Controller Implant

Switching Regulator

ASK Demodulator / DAC/Decoder

Data Modulator

PA

Battery

Vdd Shunt regulator

Rectifier

Load Shift Key

(LSK) ASK/PSK Demodulator

Encoder

L2 C2

C1

L1 To/From Other parts

Skin Power regulation at k=0.07, VREGDC = 1.8 V.


0.002 0.004 0.006 0.008 0.01

0.05

0.1

0.150.2

0.25

0.30.35

0.4Power Efficiency Versus Load Power

W/O Feedback

)2(

21

21

)2(21

21

21

22

22

11

222

DC

DC

DC

DC

VVVkPR

Vk

VVVCkPCR

CVk

dioderectload

dioderectload

total

⋅++=

⋅++=η

0.002 0.004 0.006 0.008 0.01

2

4

6

8

10Voltage of Secondary Coil Versus Load Power

W Feedback

W/O Feedback

W Feedback

II

III

IV V

Pload 1 mW 10 mW 5 mW 2mW 1 mW

9


•  Carrier Frequency : 13.56 MHz.

•  Transmission Mode : Full Duplex.

•  Modulation Methods : •  Uplink –  LSK), 100 kbps

•  Downlink –  BPSK, 1 Mbps.


BandgapVoltage

Reference

Vout

Vin

OPAMP+

-

1.26 V

LOADR2

R1

Passingtransistor

Vref

Power loss

•  Advantages of linear regulator -  Able to be fully integrated -  Less noisy.

•  Drawbacks -  Low power efficiency -  Only step-down DC-DC converter feasible.

•  To increase the power efficiency, low dropout voltage (LDO) regulator is used.

10


Bandgap Reference

- +

Vin_boost

V OH

R L1 R b1 R b2

Error Amp1 V g

NM 1 - +

V OL

R L2 R b3 R b4

Error Amp2 V g2 M 1

Vin

3.3 V 1.8 V

LDO regulators with dual-voltage output

SC DC-DC converter

Native NMOS transistor: Skips the threshold-voltage adjustment implant process.

•  V-I charts of the native NMOS passing transistor (W/L= 2400/1.2)


LOAD

LOAD IL

IH

Vrec VH

VL

3.3Vregulator

1.8Vregulator

3.3Vregulator

LOAD IH

VH

LOAD IL

VL1.8Vregulator

Vrec

Parallel/Cascade two linear regulators

SC step upDC-DC

converter

1.8V LDOregulator

3.3 V LDOregulator

BandgapReference

Start-upCircuit

StimulatorOutputStages

&Other

Circuitry

Resonancecircuit &

Full-waverectifier

VrecL

Vhigh

Vlow

Vref

Integrated on chip

Coil

Proposed Proposed Normal Normal

14.28 mW

Delivered Power

9.48 mW

Power losses

82.9% 60.6% 2.94 mW 1.6 mA 5 mA

Efficiency Stimulation current IH (3.3V)

Load current IL (1.8V)

Vrec = 3.6 V, VrecL = 2.1 V

11


Inductive link : Circuits of the voltage regulator

CLK

CC

CLK C1

Cout

Vin

M1 M2

M3

M4M6

A Vout

B

non-overlappingclock generator

M5

Vin

Q1

MP11MP10

MP09MP06MP05

MP08MP07

MN04MN03

MN02MN01 MN14

MN13

MN12

R1

VSS

MP16

MP15

Vout

R2

Q3 Q4 Q5Q2

Vin1 Vin2

Vout

M2 M4 M3M1

M5 M6

M7

M8

SC DC/DC converter The CMOS bandgap reference

Start-up circuit


The power recovering chip

SC DC/DC converter

LDO regulators

12


RF Inductive Powering : Conditioning Circuitry

•  Rectifiers: They rectify the incoming sinusoidal signal either in every cycle (full-wave rectifier) or in every other cycle (half-wave rectifier).

Half-Wave

Full-Wave

•  In each cycle (positive or negative), only 2 PMOS transistors conduct.

•  An external capacitor is also used for lowpass filtering the rectified signal to reduce its ripple.

•  Practically, integrated full-wave rectifiers are more complicated than this. Additional devices should be incorporated to protect the main transistors against high voltage and to reduce the possibility of latch-up.


Inductive link : Fully integrated solutions

RF input signal

Digital output

DC output

D2

D1

C1

C

C

R

R

R1 R2 RL

CL

T1

T2

T7T9

T3

T4 T11T5

T6

T8T10

T12

T13

T14

T15

Block cBlock a

Block b

C1

13


VAC

VOut

Gnd

RL CL

VAC

VDD

VSS

RL CL


C2

Data in

D 1 D 2 D 3 D 4

Switch Off

Req= RL/2

C2

D1

D2

D3

D4

RL

Req = RL/8

Switch On

100 kb/s 200 kb/s

LSK Modulation

D4

D3 C2 RL

RL

14



•  Introduction •  Power and data links

•  Inductive link •  Choice of carrier frequency •  Transmitted power limits •  Inductive system modeling •  Conditioning and calibration techniques

•  Discrete and integrated circuitries •  Power transfer •  Up and downlinks data transmission •  Modulation and demodulation

•  Batteries •  Miniature, rechargeable, etc.

15


Features: Switching power amplifier (AP)

Modulator Demodulator

Power link

and bi-

directional

data

Transfer

by

external

inductor

(antenna)

Processing -  Power supply management -  PA calibration -  Inductive link coupling factor

and resonance frequency calibration

-  Extensive data processing

Local frequency generator

Power source

Use

r Int

erfa

ce


Start-up Circuit

Protection Circuit

Clock Generator Circuit

Shunt regulator

Rectifier LDO Reg 1 Switched Capacitor DC/DC

Load Shift Key

(LSK)

ASK/PSK Demodulator

ADC Encoder M U X

Controller/ Stimulator

VDD1 VDD2 VDDn

Analog Front- Ends (1..n) Ti

ssue

s co

ntac

ts

Off

chip

indu

ctor

LDO Reg 2

LDO Reg n

16



•  In most high-precision cases, even the voltage ripple after lowpass filtering is not acceptable •• Use a voltage regulator

•  ~15 uA for the reference current; ~70 uA to break down the zener

diodes.

17


•  Data downlink

•  Different applications

•  Different data rates.


D

Q

QSET

CLR

D

Q

QSET

CLR

D

Q

QSET

CLR

Vcc

DATA_IN

MANCH_IN G_CLOCK

D

C

R

ASK Demodulator

Manchester Decoder

18


•  High Q > Best efficiency, but •  Envelop transition time is limited by Q-factor of receiver

•  Manchester encoding data rate is ~500 kbps @ 13.56 MHz. •  Enhance Data Rate & Power Transfer by reducing carrier OFF period.

•  Digital decoder based on carrier signal attenuation

Digitized direct in

Digitized attenuated in

Attenuation Envelop Detection Glitch Suppress

B

A R1 R2

R2

Coil

Env. Delay Majo-

rity


Direct coil Vdd + Vi VthL VthH

Dig. dir. in

Aout Bout Env

Att. coil

Dig. att. in

Vss - Vi

•  Toggling of attenuated carrier detected by toggling of direct carrier.

B

A R1 R2

R2

Coil

Env. Delay Majo-

rity

19

GBM8320 - Dispositifs Médicaux Intelligents 37 Walkins -Johnson Company Tech-nodes, Vol.7, No.5, 1980.


•  Data transmission –  BPSK Demodulator (COSTAS Loop)

Recover carrier/ data in the same loop

VCO Low Pass Filter

Data out

Data In Phase

Shifter 90

I branch

Q branch

Arm LP Filter

m(t) sin(w1t+o1) m(t) = 1 or –1

2 sin(w1t+o2)

2 cos (w1t+o2)

Gilbert multiplier

Gilbert multiplier

Gilbert multiplier

Arm LP Filter

20


GilbertMultiplier

VoltageControlledOscillator

(VCO)

QuadratureSignal

Generator

LoopFilter

Arm Filter

Arm Filter

ReceiverCoil

I branch

Q branch

Data in

Dout

GilbertMultiplier

GilbertMultiplier

Requirements: 1) Fully integrated 2) Low power consumption 3) Fully differential

Implementation of Costas loop circuit


VCO Quadrature

signal generator

Loop Filter

Arm Filter

Arm Filter Receiver coil

I branch

Q branch

Clk Dout

Data in

Chopper multiplier

Digital domain Analog domain

21


A

A

B

Z

B

B

ZABAB=⋅+⋅

B

B

Z

VIP

VIN

VQN

VQP

VQN

VQP

VQN

VOP

VON

Differential exclusive OR Chopper multiplier

Output voltage versus phase error

ππ−2π2π−2DDV2DDV−Verr

θΔ

0

Vm


Vop

VinpVinn

Von

VDD

VSS

CN

BN

CP

M1 M2

M3

M4

M5 M6 M11

M12M8M7M10

M9M13

M14

M15

M16

M17M18

M21

M22

M19

M20

M24M23

Fully differential comparator Simulation result of the comparator

PSK input

Received carrier

Hard-limited carrier

22


M11

M17

M16

M15

M14M12

M13

M18

BP

CP

CN

MP12

MP11

M9

VDD

VSS

Vinp

MN13

MN14

Vinn

Voutp

VoutnR1

C1

M1 M2

M3 M4

M5 M6

M7 M8

M10

Ic

ictrl

Vtune

D

Q

QSET

CLR

D

Q

QSET

CLR

IN

INB

OUT

OUTB

OUTQ

OUTQB

Quadrature signal generator

Relaxation Oscillator

Gm Cell

The voltage controlled oscillator (VCO)


Monolithic implementation

Simulation & Experimental results

Simulated Measured 1.25 � H 5 turns,

D = 3.5 cm

1.25 � H

0.07 Distance 1.5 0.18 µm 0.18 µm

NA 0.19 mm2 13.56 MHz 10 MHz

1.8 V 1.8V/3.3V

Parameters Transmitter Coil (PCB)

Receiver Coil (PCB) Coefficient Tech CMOS Circuit area

Carrier Freq. Supply Volt.

14.7 M 13.5 M rad/s 1.51 Mbps 1.12Mbps

652 � W 610 � W

VCO gain Data rate

Power Cons.

BER NA 1.00E-04

5 turns, D = 2.7 cm

ASK demodulators

Data rate (kbps)

Power consumption

[LIU2000] [AKI1998]

< 250 N/A < 125 2 mW

VCO Data out

Phase Shifter 90

I branch

Q branch LPF

Input Signal

LPF LPF

23


~10 Mbps < 1 mW

LPF

-

+

Vd(t)

Cos(w1t+q2)

VCO Input Signal

Vs(t)

90 - Phase Shifter

Data Out A

Data Out B

LPF

LPF

Sin(w1t+q2)

VCO

Data out

Phase Shifter 90

I branch

Q branch LPF

Input Signal

LPF

LPF

QPSK

CMOS 0.18µm

13.56 MHz

>10* Mbps 8.0** Mbps

~1.0 mW**

BPSK

CMOS 0.18µm

13.56 MHz

1.6* Mbps* 1.2*

Mbps**

0.61 mW**


Low-power transceiver

~ 1 mW > 100 kb/s

Regulated LC-VCO

24


•  Functional tests (electrical, mechanical, ..) •  Circuits, Package, Heat, Reliability, Toxicity, ….

•  Self-test and fault detection after implantation •  Noise considerations and grounding (multichannel aspect) •  Analog/digital blocks, Scan and BIST, overhead resources power/area

•  In vivo measurement and validation •  Humidity, temperature, Ion concentration, pH, interface to tissues,… •  Experiments in animals and humans: spontaneous or evoked activity

•  Ethics, experimental protocol and approvals.


RF Inductive Powering : Battery

Nominal Voltage = 1.55V

25





Recharge

Regulator5VPower Supply

ControlUnit

FPGA

Enable+

-

Discharge

DC/DC Up

Converter3.3V~3.7V

GND

RL

Recharge

Regulator5VPower Supply

ControlUnit

FPGA

Enable+

-

Discharge

DC/DC Up

Converter3.3V~3.7V

GND

RL

1

2

3

Voltage (V)

Duration (h)0200 400 400 800

@ 37ºC200uA Load

1

2

3

Voltage (V)

Duration (h)0200 400 400 800

@ 37ºC200uA Load

•  Rechargeable Battery: •  3V, 100mAh •  1000 Cycles of 10%

discharge

Introduction Inductive link - Polytechnique Montréal · PDF file• Introduction...

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