introduction inductive link - polytechnique montréal · pdf file• introduction...
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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.
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GBM8320 - Dispositifs Médicaux Intelligents 3
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
GBM8320 - Dispositifs Médicaux Intelligents 4
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
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GBM8320 - Dispositifs Médicaux Intelligents 5
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
GBM8320 - Dispositifs Médicaux Intelligents 6
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
GBM8320 - Dispositifs Médicaux Intelligents 7
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 / �)
GBM8320 - Dispositifs Médicaux Intelligents 8
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.
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GBM8320 - Dispositifs Médicaux Intelligents 9
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
inductive link rectifier linear regulator
~
Vrec VoltageRegulator
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.
GBM8320 - Dispositifs Médicaux Intelligents 10
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
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GBM8320 - Dispositifs Médicaux Intelligents 11
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:
GBM8320 - Dispositifs Médicaux Intelligents 12
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
inductive link rectifier linear regulator
~
Vrec VoltageRegulator
R2
Primary resonant
signal
Secondary induced signal
Rectified voltage (half
rectifier)
Regulated voltage supply
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GBM8320 - Dispositifs Médicaux Intelligents 13
VDC
LOAD
* *R1
MC1
L1 L2 C2Vs
C3
inductive link rectifier linear regulator
~
Vrec VoltageRegulator
R2
rflink=
Zr
Z1
=k 2 R2C2
R1C1 + k 2 R2C2 rectifier=
Vrect
Vrect + 2Vdiode regulator≈
VDC
Vrect
� � �
GBM8320 - Dispositifs Médicaux Intelligents 14
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
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GBM8320 - Dispositifs Médicaux Intelligents 15
+-
* *
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.
GBM8320 - Dispositifs Médicaux Intelligents 16
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
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GBM8320 - Dispositifs Médicaux Intelligents 17
• Carrier Frequency : 13.56 MHz.
• Transmission Mode : Full Duplex.
• Modulation Methods : • Uplink – LSK), 100 kbps
• Downlink – BPSK, 1 Mbps.
GBM8320 - Dispositifs Médicaux Intelligents 18
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.
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GBM8320 - Dispositifs Médicaux Intelligents 19
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)
GBM8320 - Dispositifs Médicaux Intelligents 20
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
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GBM8320 - Dispositifs Médicaux Intelligents 21
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
GBM8320 - Dispositifs Médicaux Intelligents 22
The power recovering chip
SC DC/DC converter
LDO regulators
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GBM8320 - Dispositifs Médicaux Intelligents 23
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.
GBM8320 - Dispositifs Médicaux Intelligents 24
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
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GBM8320 - Dispositifs Médicaux Intelligents 25
VAC
VOut
Gnd
RL CL
VAC
VDD
VSS
RL CL
GBM8320 - Dispositifs Médicaux Intelligents 26
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
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GBM8320 - Dispositifs Médicaux Intelligents 27
GBM8320 - Dispositifs Médicaux Intelligents 28
• 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
GBM8320 - Dispositifs Médicaux Intelligents 29
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
GBM8320 - Dispositifs Médicaux Intelligents 30
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
GBM8320 - Dispositifs Médicaux Intelligents 31
GBM8320 - Dispositifs Médicaux Intelligents 32
• 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
GBM8320 - Dispositifs Médicaux Intelligents 33
• Data downlink
• Different applications
• Different data rates.
GBM8320 - Dispositifs Médicaux Intelligents 34
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
GBM8320 - Dispositifs Médicaux Intelligents 35
• 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
GBM8320 - Dispositifs Médicaux Intelligents 36
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.
GBM8320 - Dispositifs Médicaux Intelligents 38
• 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
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GBM8320 - Dispositifs Médicaux Intelligents 39
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
GBM8320 - Dispositifs Médicaux Intelligents 40
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
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GBM8320 - Dispositifs Médicaux Intelligents 41
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
GBM8320 - Dispositifs Médicaux Intelligents 42
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
GBM8320 - Dispositifs Médicaux Intelligents 43
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)
GBM8320 - Dispositifs Médicaux Intelligents 44
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
GBM8320 - Dispositifs Médicaux Intelligents 45
~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**
GBM8320 - Dispositifs Médicaux Intelligents 46
Low-power transceiver
~ 1 mW > 100 kb/s
Regulated LC-VCO
24
GBM8320 - Dispositifs Médicaux Intelligents 47
• 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.
GBM8320 - Dispositifs Médicaux Intelligents 48
RF Inductive Powering : Battery
Nominal Voltage = 1.55V
25
GBM8320 - Dispositifs Médicaux Intelligents 49
RF Inductive Powering : Battery
GBM8320 - Dispositifs Médicaux Intelligents 50
RF Inductive Powering : Battery
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