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Inductively coupled UHF RFID transponder for implanted medical devices 1.

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Presentation on theme: "Inductively coupled UHF RFID transponder for implanted medical devices 1."— Presentation transcript:

1 Inductively coupled UHF RFID transponder for implanted medical devices 1

2 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

3 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 cant 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.

4 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

5 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: modulator 810um 400um A B C D E F G Fig.2 LayoutFig.3 Test board

6 6 SPECIFICATION Reader ( mixer, power amp ) Frequency900 MHz (Carrier) ASK data rate160 kbps Modulation depth90 % Duty cycle70 % RF power0.5 W (27 dBm) Transponder (integrated chip) VDD1.5 V1.54 V Charging Current260 uA Charging Voltage1.5 V1.466 V Modulator data rate320 Kbps Table.1. Specification Introduction

7 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 input Fig.4 Rectifier Circuit Fig.5 Rectifier operation theory Voltage ripple

8 Circuit description (DC supplying) 8 Regulator To supply the constant voltage Power consumption: 23uW Regulated output voltage : 1.54V Fig.6 Regulator circuitFig.7 Gain and Phase of a regulator Phase margin 50 Kohm 23 Kohm 1 V Gain : 3.3 dB Unit gain frequency : 35 MHz Phase margin : 78 o ( stable ) a b

9 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 referenceFig.9 Measured regulator output 1.72 V 1V Vth 0.43 V V 1.54V X Y

10 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

11 Circuit description (charging mode) 11 Charging circuits Power consumption: 69uW (charging circuit, opamp(A), comparator(B)) Charging circuit conversion efficiency : ( I battery /I input ) * 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 off on c z

12 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 * d Constant current region 28 s 1.466V

13 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 encodingFig.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

14 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 signalFig.19 Demodulator circuit

15 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

16 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 modulationFig.23 Measurement setup for a load modulation

17 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 oscillatorFig.25 Measured oscillator output

18 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 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 antenna Receiver antenna Transponder antenna

20 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 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

22 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: V Fig.35 Constant current for different distance 1.478V 27 s

23 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 Return to 1 encoding Demodulator output A B Fig.36 Block diagram for a communication

24 24 Measured backscattering modulator Input data rate : 320Kbps Encoding : Manchester encoding Difference of high and low (Fig.39 B): 5 mV 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 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 Transponder inductor Test board

26 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 inductorFig.43 Return loss -29dB Power transfer method (inductive coupling)

27 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)

28 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

29 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 Return to 1 encoding Demodulator output Fig.49 Block diagram for a communication A B

30 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 Manchester encoding Receiver inductor signal Fig.51 Block diagram for a communication A B

31 31 Table.2. Comparisons of conventional circuits This workConventional [1] IEEE 2007 This workConventional[2] JSSC 2006 Power transfer method Inductive couplingEM wave Frequency900 MHz4 MHz900 MHz950MHz Operating VDD Charging voltage, current V 260 uA 4.1 V 1.5 mA V 260 uA x Charging efficiency 4.48 %73 %4.48 %x communicationuplink, downlink xuplink, downlink uplink, downlink Maximum comm. distance 6.5 mmx1.8 m10 m Antenna dimension 5mm X 6 mm -PCB (FR4) 9mm (diameter) -Coil with ferrite core Dipole antenna mm Dipole antenna mm Comparisons of conventional circuits

32 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)

33 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 [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 , Oct

34 34 Q & A

35 35 Rectifier Rectifier sensitivity Rectifier output voltage for the frequency Rectifier efficiency : 5.58 % (Load 10Kohm, Input power 3dBm) Fig.1 Measured rectifier sensitivityFig.2 rectifier output voltage for different frequency load 10Kohm 3 dBm 1.05 V APPENDIX 1

36 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 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

38 APPENDIX 4 38 Fig.4 Regulator schematic Regulator schematic

39 APPENDIX 5 39 Fig.5 Demodulator schematic Demodulator schematic

40 APPENDIX 6 40 Fig.7 Modulated input signal Fig.6 Demodulator input and Averaging signalFig.8 Demodulator output Simulation result Communication mode

41 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 Fig.22 Block diagram for a communication

42 APPENDIX 8 42 Fig.9 Smith chart for a conjugate matching Conjugate matching network Fig.10 Matching network

43 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 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 mW ~ mW Fig.14 Available power for different distanceFig.13 Available power measurement method APPENDIX 10

45 APPENDIX 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)

46 APPENDIX 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


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