Inductively coupled UHF RFID transponder for implanted medical devices 1.
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Transcript of Inductively coupled UHF RFID transponder for implanted medical devices 1.
Inductively coupled UHF RFID transponder
for implanted medical devices
1
광주 과기원
발표자 김광순
2
Contents Motivation Introduction Circuit Description DC supplying circuits Charging mode Communication mode
Power transfer method Electro Magnetic wave (antenna to antenna) Inductive coupling (inductor to inductor)
Comparison of Conventional Circuits Conclusion / Reference
Motivation
3
Conventional RFID transponder• The conventional UHF RFID transponder size is too large(because of antenna)• The radiation of a antenna is injurious to a body.• Without the reader (external device), the transponder can’t be operated
Implanted medical device• Because the device is implanted in the body, the battery is necessary to operate the implanted medical device• The implanted device requires maintenance of the battery which requires regular surgery
Solution• If the inductor antenna is used at the UHF, the transponder size can be small. • Because the transponder battery is charged by the incident RF power , it can prevent regular surgery in the implanted medical device• The effect on a body is lower than EM wave method since the inductor antenna is operated by magnetic coupling.
Introduction
4
Fig.1 Total Block Diagram
Transponder Composition•External antenna
•Matching network
•Rectifier/Regulator/Switch
•Battery charging circuit
•Demodulator/Modulator/Oscillator
Reader Composition• Mixer, Power Amp
• Transmitter Antenna
• Receiver antenna
Integrated chip
Introduction
5
Test board•COB(chip on a board) packaging
Process / Layout• Samsung 0.18um process (MPW)
• Dimension: 810um X 400um
• A: rectifier B: regulator C: switch
• D: charging circuit, opamp, comparator
• E: oscillator F: demodulator G: modulator810um
400um A
B
C
D E
F
G
Fig.2 Layout Fig.3 Test board
6
SPECIFICATION
Reader( mixer,
power amp )
Frequency 900 MHz (Carrier)
ASK data rate 160 kbps
Modulation depth 90 %
Duty cycle 70 %
RF power 0.5 W (27 dBm)
Transponder(integrated chip)
VDD 1.5 V 1.54 V
Charging Current 260 uA 260 uA
Charging Voltage 1.5 V 1.466 V
Modulator data rate 320 Kbps 320 Kbps
Table.1. Specification
Introduction
Circuit description (DC supplying)
7
Rectifier• To convert the sinusoidal to DC power
• Simple structure
• Storage cap :
- C4 for prevent the voltage ripple
• Rectifier output :
- for DC supplying
• Demodulator inputFig.4 Rectifier Circuit
Fig.5 Rectifier operation theory
Voltage ripple
Circuit description (DC supplying)
8
Regulator• To supply the constant voltage
• Power consumption: 23uW
• Regulated output voltage : 1.54V
Fig.6 Regulator circuit Fig.7 Gain and Phase of a regulator
5_
4 5regulaotr output ref
RV V
R R=
+50
1.5 1.0250 23
kV V
k k=
+
Phase margin 50 Kohm
23 Kohm1 V
•Gain : 3.3 dB
•Unit gain frequency : 35 MHz
•Phase margin : 78o ( stable )
-------- a
------ b
Circuit description (DC supplying)
9
Regulator• Limiter : To prevent the damage of circuits at the high power
• Voltage reference : To supply constant reference voltage to a opamp
Fig.8 Limiter and Voltage reference Fig.9 Measured regulator output
1.72 V
1V
Vth 0.43 V
Vth 0.43 V
Vth 0.43 V
Vth 0.43 V
+
+
+1.5V
1.54VX
Y
Circuit description (DC supplying)
10
Fig.10 Switch
Fig.12 Communication mode
Switch• To change a charging mode and a communication mode
Fig.11 Charging mode
0 1
Circuit description (charging mode)
11
Charging circuits• Power consumption: 69uW (charging circuit, opamp(A), comparator(B))
• Charging circuit conversion efficiency
: ( Ibattery/Iinput ) * 100 =
(195 uA / 241 uA ) *100 = 81 %
at VDD = 1.5V
Fig.14 Charging circuitFig.13 Block diagram for a charging circuit
1.1*I
I
100*I
195 uA
1.1*I
2.1*I
241 uA
1.5V
offon
------ c
z
Circuit description (charging mode)
12
Charging circuit• Direct RF input power : 9.2 dBm (8.32mW, 900 MHz (CW))
• Constant current: 260uA , Charging Voltage :1.466 V
• Rechargeable battery for the measurement : 3.96 mF capacitor
• EOC(end of charging) voltage: 1.447V
• Total charging efficiency:
=( 0.39mW /8.32mW ) * 100
= 4.68 %
Charging power = 260uA * 1.5V
Fig.15 Measured charging profile
charging power
RF input power* 100 ------ d
Constant current region
28 s
1.466V
Circuit description (communication mode)
13
Reader to Transponder (Downlink)
• Carrier frequency : 900 MHz
• Data rate:160 Kbps
• Modulation depth : 90 %
• Duty cycle : 70 %
• ASK modulation
• Digital encoding: Return to 1
- In order to transmit continuous
power to a transmitter
Fig.16 Return to 1 encoding Fig.17 Manchester encoding
Transponder to Reader (Uplink)
• Data rate:320 Kbps
• Duty cycle : 50 %
• Backscattering modulation
- EM wave method
• Load modulation
- Inductive coupling method
• Digital encoding: Manchester coding
Circuit description (communication mode)
14
Demodulator• Minimum input power to operate a demodulator : 1.67dBm
• Low pass filter
- To terminate the high frequency component
• Power consumption: 54 uW
• Hysteresis comparator :
- Good for noise immunity
Fig.18 Demodulator input and averaging signal Fig.19 Demodulator circuit
Circuit description (communication mode)
15
Backscattering modulator (EM wave method)• To transmit the data to a reader
• The change of a reflected power (backscattering modulation)
• The modulation due to the changed matching network
Fig.20 Backscattering modulation Fig.21 Measurement setup for backscattering modulation
Circuit description (communication mode)
16
Load modulator (inductive coupling)• To transmit the data to a reader
• The change of a coupling coefficient
• The modulation due to the changed matching network
Fig.22 Load modulation Fig.23 Measurement setup for a load modulation
Circuit description (communication mode)
17
Ring oscillator• 5-stage inverter ring oscillator
• Oscillation frequency: 210KHz
• To supply the clock
• Data rate of load modulator
• Power consumption: 63uW
Fig.24 Ring oscillator Fig.25 Measured oscillator output
Power transfer method
18
Fig.26 Total Block Diagram
Power transfer method• Electromagnetic wave – antenna to antenna ( yagi-uda – dipole )
• Inductive coupling – inductor to inductor (1turn inductor – 2 turn inductor)
19
Fig.27 EM wave experiment setup
Electro-magnetic wave • Distance of a reader and a transponder : 1m
• Transmitter antenna power : 27 dBm
Power transfer method (EM wave)
Transmitter antennaReceiver antenna
Transponder antenna
20
Fig.28 Yagi antenna
Yagi antenna (Reader)• 10 dB bandwidth : 170 MHz
• VSWR : 1.06 at 900 MHz
• Gain : 5.83 dBi
• 50 ohm Source
• Directional antenna
• Simulator : CST
Fig.29 Yagi antenna
Fig.30 Return loss
Power transfer method (EM wave)
21
Fig.31 Dipole antenna
Dipole antenna (transponder)• 10 dB bandwidth : 140 MHz
• VSWR : 1.16 at 900 MHz
• Gain : 1.88 dBi
• 50 ohm Source
• Simulator : CST
Fig.33 Return loss
Power transfer method (EM wave)
Fig.32 Dipole antenna
Power transfer method (EM wave)
22
Fig.34 Measured charging profile
Measured charging mode• Reader output power : 27 dBm (900 MHz (CW))
• Constant current: 254uA , Charging Voltage :1.478 V – distance 0.8m
• Rechargeable battery for the measurement : 3.96 mF capacitor
• EOC(end of charging) voltage: 1.445 V
Fig.35 Constant current for different distance
1.478V
27 s
Power transfer method (EM wave)
23
Measured demodulator output signal• Reader output power : 27 dBm
• The distance for measurement : 1 m
• Modulation : ASK (160 Kbps data rate)
• Encoding : return to 1
• Maximum comm. Distance : 1.8 m
Fig.37 Demodulator output data stream for arbitrary input data
01 0 1 1 0 0 0 1 0 01 1 10 1
01 0 1 1 0 0 0 1 0 01 1 10 1
Return to 1 encoding
Demodulator output
A
B
Fig.36 Block diagram for a communication
24
Measured backscattering modulator• Input data rate : 320Kbps
• Encoding : Manchester encoding
• Difference of high and low (Fig.39 B):
5 mV
0 10 1 00 11 0 1 1 0 0 1 1 0
0 10 1 00 11 0 1 1 0 0 1 1 0
Manchester encoded data
Power transfer method (EM wave)
Fig.39 Modulated signal by a transponder
Receiver antenna signal
A
B
Fig.38 Block diagram for a communication
25
Fig.40 Inductive coupling measurement setup
Inductive coupling• Distance of a Reader and a transponder : 4 mm
• Power amp output power : 27 dBm
Power transfer method (inductive coupling)
Transmitter inductor
Receiver inductor
TransponderinductorTest board
26
Fig.42 transmitter inductor smith chart
Transmitter inductor• SRF(self resonance frequency) : 1.3 GHz
• Inductance : 56 nH at 900 MHz
• Q Value : 90 at 900 MHz
Impedance matching• For maximum power transfer(50 ohm feed)
Fig.41 Reader inductor matching / Reader inductor Fig.43 Return loss
-29dB
Power transfer method (inductive coupling)
27
Fig.44 transponder inductor /conjugate matching network
Transponder inductor• SRF(self resonance frequency) : 1.39 GHz
• Inductance :32nH at 900 MHz
• Q Value : 83 at 900 MHz
• Inductor dimension : 6 mm X 5 mm
Impedance matching• Conjugate matching
Fig.46 Return loss
Fig.45 Transponder inductor smith chart
Power transfer method (inductive coupling)
Power transfer method (inductive coupling)
28
Fig.47 Measured charging profile
Measured charging mode• Reader output power : 27 dBm (900 MHz (CW))
• Constant current: 268uA , Charging Voltage :1.457 V – distance 6.5mm
• Rechargeable battery for the measurement : 3.96 mF capacitor
• EOC(end of charging) voltage: 1.44 V
Fig.48 Constant current for different distance
1.457V
26 s
Power transfer method (inductive coupling)
29
Measured demodulator signal• Reader output power : 27 dBm
• Modulation : ASK (amplitude shift keying)
• Encoding : return to 1
• The distance for measurement : 4 mm
• Maximum comm. Distance : 6.5 mm
Fig.50 Demodulator output data stream for arbitrary input data
1 00 0 11 11 0 1 0 1 0 0 1 0
1 00 0 11 11 0 1 0 1 0 0 1 0
Return to 1 encoding
Demodulator output
Fig.49 Block diagram for a communication
A
B
Power transfer method (inductive coupling)
30
Measured load modulator• Input data rate : 320Kbps
• Manchester encoding
• The difference of high level and low level
: 4 mV
Fig.52 modulated signal by a transponder
00 1 00 01 1 0 0 1 0 1 1 1
00 1 00 01 1 0 0 1 0 1 1 1
Manchester encoding
Receiver inductor signal
Fig.51 Block diagram for a communication
A
B
31
Table.2. Comparisons of conventional circuits
This work Conventional [1]IEEE 2007
This work Conventional[2]
JSSC 2006
Power transfer method
Inductive coupling EM wave
Frequency 900 MHz 4 MHz 900 MHz 950MHz
Operating VDD 1.54 4.1 1.54 1.5
Charging voltage, current
1.457 V260 uA
4.1 V1.5 mA
1.478 V260 uA
x
Charging efficiency
4.48 % 73 % 4.48 % x
communication uplink,downlink
x uplink,downlink
uplink,downlink
Maximum comm. distance
6.5 mm x 1.8 m 10 m
Antenna dimension
5mm X 6 mm-PCB (FR4)
9mm (diameter)-Coil with ferrite core
Dipole antenna- 160 mm
Dipole antenna- 160 mm
Comparisons of conventional circuits
Conclusion
32
Implanted medical device - Because the inductor antenna is used at the UHF, the transponder size can be small.
(inductor dimension : 5mm X 6 mm)
- The transponder battery is charged by the incident RF power , it can prevent
regular surgery in the implanted medical device.
(Charging voltage =1.5V , charging current =260uA,
power consumption of charging mode = 92 uW)
- Due to the wireless communication, the reader receives the information from a body easily.
(Communication mode power consumption = 160 uW, communication distance = 6.5 mm)
- The effect on a body is lower than EM wave method since the inductor antenna is operated by magnetic coupling. (Inductive coupling)
Reference
33
[1] Toshiyuki Umeda, “A 950-MHz Rectifier Circuit for Sensor Network Tags With 10-m Distance”, IEEE J. Solid-State Circuits, vol. 41, No. 1, pp.35-41, Jan. 2006 .
[2] Pengfei Li, “A Wireless power Interface for Rechargeable Battery Operated Medical Implants”, IEEE Transactions on Circuits and Systems II: Express Briefs 54 (10), pp. 912-916 , Oct. 2007.
34
Q & A
35
Rectifier• Rectifier sensitivity
• Rectifier output voltage for the frequency
• Rectifier efficiency : 5.58 % (Load 10Kohm, Input power 3dBm)
Fig.1 Measured rectifier sensitivity Fig.2 rectifier output voltage for different frequency
load 10Kohm
3 dBm
1.05 V
APPENDIX 1
APPENDIX 2
36
Fig.3 Charging Profile
Battery Charging Profile• Constant Current (fast charging)
• Constant Voltage (slow charging)
• End of Charging
Silver Zinc rechargeable battery• High Energy Density
- 40% more than lithium-ion
- Increase run time
- Smaller size
• Nominal Voltage = 1.5V
• Safety (No lithium)
37
Characteristic of charging circuit• Direct RF input power
• The variety of Charging current :
Due to the varying incident power
• Minimum charging current : 180 uA
Fig.16 Measured Charging current for different input power
APPENDIX3
Fig.17 Measured EOC voltage for different input power
APPENDIX 4
38Fig.4 Regulator schematic
Regulator schematic
APPENDIX 5
39Fig.5 Demodulator schematic
Demodulator schematic
APPENDIX 6
40
Fig.7 Modulated input signal
Fig.6 Demodulator input and Averaging signal Fig.8 Demodulator output
Simulation result• Communication mode
APPENDIX 7
41
Demodulator• Direct input power : 6 dBm
• Modulation : ASK (amplitude shift keying)
• Encoding : return to 1
• Arbitrary transmitter data stream
• Demodulator output data stream
• Sensitivity : 1.67 dBm
Fig.23 Demodulator output data stream for arbitrary input data stream
01 0 1 1 0 11 0 0 0 1 1 0 1 0
01 0 1 1 0 11 0 0 0 1 1 0 1 0
Fig.22 Block diagram for a communication
APPENDIX 8
42Fig.9 Smith chart for a conjugate matching
Conjugate matching network
Fig.10 Matching network
43
Fig.11 Available power measurement method
Available power• Measurement of Rectifier output voltage
- Load 10 Kohm
• Antenna input power: 27 dBm (500 mW)
• Available power
: 625uW at the distance 1.05 m
Fig.12 Available power for different distance
APPENDIX 9
44
Inductive coupling• Measurement of rectifier output voltage
- Load 10 Kohm
• Reader output power: 27 dBm
• 19mm X 19mm at the distance 9.4 mm
- Area of the voltage variance 0.625 mW ~ 0.225 mW
Fig.14 Available power for different distanceFig.13 Available power measurement method
APPENDIX 10
APPENDIX 11
45
Modulator spectrum for arbitrary input data with Manchester encoding
Fig.15 Backscattering modulator spectrum for arbitrary input data (Manchester encoding)
Fig.16 Load modulator spectrum for arbitrary input data (Manchester encoding)
APPENDIX 12
46
Fig.17 Backscattering modulator spectrum for 320 KHz NRZ encoding
Fig.18 Load modulator spectrum for arbitrary 320 KHz NRZ encoding
Modulator spectrum for 320 KHz with NRZ encoding