Inductively coupled UHF RFID transponder for implanted medical devices

Inductively coupled UHF RFID transponder for implanted medical devices
광주 과기원 발표자 김광순 The title is inductively coupled UHF RFID transponder for implanted medical devices.

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 This slide is contents. this is mainly composed 6 parts ; Motivation, a introduction, a circuit description, a power transfer method, comparison of conventional circuits and conclusion/reference. the circuit description contains Dc supplying circuit, charging mode circuit, and a communication circuit. the power transfer method contains Electromagnetic wave method, and inductive coupling.

Motivation Conventional RFID transponder Implanted medical device
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. The conventional uhf RFID transponder size is too large. Without the reader, a transponder can’t be operated. In applications of implanted medical devices, since the device is implanted in the body, the battery is necessary to operate the implanted medical device. and, the implanted devices requires maintenance of the battery which requires regular surgery. In order to solve this problem, if the inductor antenna is used at the UHF, the transponder size can be small. And since, the inductor antenna is operated by magnetic coupling, the effect for a body is lower than EM wave method. In addition, a transponder contains the charging circuit and the secondary battery, a secondary battery is charged by the incident RF power. This method can solve the conventional transponder problems.

Introduction Transponder Composition Reader 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 Fig.1 shows the total block diagram. This system is composed of the reader and the transponder. A reader is similar to the base station. This is composed of a mixer, a power amp, a transmitter antenna and a receiver antenna. A transponder is composed of a external antenna, a matching network and a integrated chip. In a integrated chip is divided DC suppling part, battery charging part, communication part; Fig.1 Total Block Diagram

Introduction Test board Process / Layout
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 The integrated chip is fabricated by the Samsung 0.18 um process. Fig.2 shows the layout of a integrated chip. Total size is 810um X 400 um. Fig.3 shows the test board for measurements. The packaging type of a fabricated chip is cob. The bare chip and a PCB board is directly connected by gold wires. Fig.2 Layout Fig.3 Test board

Introduction SPECIFICATION Reader ( mixer, power amp ) Frequency
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 shows the specification of a reader and a transponder. The reader have carrier frequency 900 MHz, modulation depth 90 % ,duty cycle 70 % and 0.5 W RF power. The operating voltage of transponder is 1.5 V. a charging current is 260 uA. A charging voltage is 1.5V . Modulation data rate 320 kbps. The yellow line is simulation results. Red line is measurement results Table.1. Specification

Circuit description (DC supplying)
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 Voltage ripple Fig.4 shows the rectifier circuit. The rectifier is used for converting from the sinusoidal wave to DC. When the sinusoidal wave is converted to DC, voltage ripple comes out. In order to prevent high voltage ripple, capacitor C4 is used. the value is 0.5 nF Also, the demodulator input signal for communication is extracted by TR m5. Fig.5 Rectifier operation theory

Regulator To supply the constant voltage Power consumption: 23uW Regulated output voltage : 1.54V Gain : 3.3 dB Unit gain frequency : 35 MHz Phase margin : 78o ( stable ) a 50 Kohm 23 Kohm 1 V b Phase margin Fig.6 shows the regulator circuit. A regulator is composed of a preamp, a pass transistor M18, and series resistors R4,R5. the incident power of a rectifier is varied for different distance. so that, The rectifier output voltage is varied So, a regulator requires to provide a constant voltage 1.5V. a regulator use a feedback loop to maintain a constant output voltage. To have a stable loop, the phase margin is higher than degree 45. Fig.7 shows the relation of phase and gain. Here, Phase margin of a regulator is degree 78. so this is stable. In addition, a regulator output voltage, series resistors, and a regulator output voltage is determined by equation a . So, reference voltage is 1V,and the value of series resistors is 23 Kohm, 50 Kohm. Fig.6 Regulator circuit Fig.7 Gain and Phase of a regulator

Regulator Limiter : To prevent the damage of circuits at the high power Voltage reference : To supply constant reference voltage to a opamp 1.72 V 1.54V X Vth V + 1V 1.5V Y Fg.8 shows the limiter circuit and the voltage reference. Limiter circuit is used for preventing the damage of circuits at the high power. In a limiter circuit, when the output voltage of rectifier is higher than the summation of threshold hold voltage of mos connected diode, the overdue current flow through the M6. so, the damage by high voltage is prevented. This circuit is voltage reference circuits. The circuit provide reference voltage 1V. Fig.9 shows the simulation and measurement of a regulator for different input voltage. The simulated regulator voltage is 1.5V and the measured regulator voltage is 1.54V. The difference is caused by process variation of series resistors. Fig.8 Limiter and Voltage reference Fig.9 Measured regulator output

Switch To change a charging mode and a communication mode Fig.11 Charging mode 1 The switch is used for changing of a charging mode and a communication mode. A switch is composed of transmission gates and inverters. When the switch input is ‘0’, the current flows the battery charging circuit. When the switch is ‘1’, the current flow the demodulator, the modulator and the internal oscillator.. Fig.10 Switch Fig.12 Communication mode

Circuit description (charging mode)
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 241 uA 1.5V c 1.1*I 100*I z on I 1.1*I off 195 uA Fig.14 is charging circuit. The charging circuit contains the opamp and the comparator. The operation theory of a charging circuit is that the 2.1*I current is flow through transistor M10. this current is summation of current of node x and node z. at this time, transistor M8 is off, so the current don’t flow through M8. the current 100I is mirrored from the transistor M11, this current flow the battery. so, battery voltage is increased. When the battery voltage is higher than the reference of opamp, A opamp A drives the transistor M8. so, the current 1.1*I is steered to transistor M8. the EOC signal is generated by comparing the voltage difference between node x and node y The power consumption of charging circuit is 69 uW. And charging efficiency calculated the equation A is 81 %. 2.1*I Fig.13 Block diagram for a charging circuit Fig.14 Charging circuit

Circuit description (charging mode)
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 Constant current region charging power * 100 d RF input power 1.466V Fig.15 shows the measured charging profile for direct RF input power. Direct input power is 9.2 dBm, and the frequency is 900MHz continuous wave. this region is constant current. The charging current is 260 uA. And the charging voltage is 1.466V. EOC signal comes out at the 28 second. at this time, the battery voltage is The 3.96mF capacitor is used for measuring the charging profile Instead of the battery. And the total charging efficiency calculated the equation A is 4.68 %. 28 s Fig.15 Measured charging profile

Circuit description (communication mode)
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 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 At the communication mode, Downlink, UPlink, is different. In the data transfer from reader to a transponder, the carrier frequency is 900MHz, modulation method is ASK. Data rate is 160 kbps. Also, while the reader transmit the data to transponder, the power has to be delivered continually. So that the return to 1 encoding method is applied. Fig.16 shows the return to 1 encoding. It is possible to ensure a continuous power supply to the transponder from reader even during data transfer. In data transfer from transponder to a reader, data rate is 320 kbps, duty cycle is 50% , the modulation method is backscattering modulation and load modulation. A backscattering modulation is applied to the EM wave method. A load modulation method is applied to inductive coupling. A backscattering modulation and a load modulation method will be explained after this. And the digital encoding method is Manchester encoding. Fig.17 shows the Manchester encoding. Fig.16 Return to 1 encoding Fig.17 Manchester encoding

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.19 shows the demodulator circuit. It is composed of the low pass filter and the averaging circuit and a hysteresis comparator. When the modulated signal go into rectifier, transistor m5 extracts the demodulator input signal. The signal is a demodulator input signal. A demodulator input signal is divided by a averaging circuit. So that, the demodulator output signal is generated by comparing the voltage difference between a demodulator input signal and a averaging signal. Fig.18 Demodulator input and averaging signal Fig.19 Demodulator circuit

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 ,21 shows the backscattering modulation principle. Here this is a modulator. The modulator is composed of a transistor and a capacitor. The theory is similar to the radar. The incident power of the reader is reflected by transponder antenna. and then The matching network is changed by modulator input data. At the result, the reflected power is changed. A reader detects the difference of reflected power. With this theory, a reader receive the data. Fig.20 Backscattering modulation Fig.21 Measurement setup for backscattering modulation

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 ,23 shows the load modulation principle. The basic theory is similar to backscattering modulator. the difference is that reader inductor detects the changing of coupling coefficient between the reader inductor and transponder inductor. A reader receives the data with the detection of changed coupling coefficient. And, at the measurement setup, because of the magnetic coupling between transmitter inductor and test wires, correct measurement is difficult. So, the magnetic coupling is minimized by using shield wires. Fig.22 Load modulation Fig.23 Measurement setup for a load modulation

Ring oscillator 5-stage inverter ring oscillator Oscillation frequency: 210KHz To supply the clock Data rate of load modulator Power consumption: 63uW Fig.24 shows the ring oscillator. This is composed of 5 stage inverter. . Fig.25 show the measured result. A oscillator is used for providing the clock. And the power consumption is 63uW. Fig.24 Ring oscillator Fig.25 Measured oscillator output

Power transfer method Power transfer method
Electromagnetic wave – antenna to antenna ( yagi-uda – dipole ) Inductive coupling – inductor to inductor (1turn inductor – 2 turn inductor) this slide shows the power transfer method. Power transfer method is 2. one is the electromagnetic wave. Another is inductive coupling method. Electromagnetic wave is used for long distance (between 1m ~ 10m ). The antenna is used for transferring power. Inductive coupling method is used for short distance (<1m ). The inductor is used for transferring power. Fig.26 Total Block Diagram

Power transfer method (EM wave)
Electro-magnetic wave Distance of a reader and a transponder : 1m Transmitter antenna power : 27 dBm Receiver antenna Transmitter antenna Transponder antenna Fig.27 shows the EM wave experiment setup. The reader is composed of a transmitter antenna, a mixer, a power amp and a receiver antenna. a mixer is used for producing the ASK modulation signal. And transmitter antenna power is 27dBm. The test board is composed transponder antenna, integrated chip, rechargeable battery. 2 multimeters are used for measuring the charging voltage and charging current at once. And with the oscilloscope, the demodulator output of a integrated chip is measured. A receiver antenna detects the backscattered signal from the transponder antenna. Fig.27 EM wave experiment setup

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.28,29 shows yagi uda antenna for transmitter antenna. the fabricated antenna is composed a reflector, a director and feed dipole. By Using the reflctor and direictor, the antenna gain can be increased. The gain is 5.83dBi. the 10dB bandwidth of the yagi antenna is 170MHz. VSWR is 1.06 at 900MHz. Used simulator is CST EM simulator. Fig.30 shows the return loss. The red line is a measurement result. The blue line is a simulation result. Fig.28 Yagi antenna Fig.30 Return loss

Dipole antenna (transponder) 10 dB bandwidth : 140 MHz VSWR : 1.16 at 900 MHz Gain : 1.88 dBi 50 ohm Source Simulator : CST Fig.32 Dipole antenna Fig.31,32 shows a dipole antenna for transponder antenna. the 10dB bandwidth of the yagi antenna is 140MHz. . VSWR is 1.16 at 900MHz.The gain is 1.88dBi Used simulator is CST EM simulator. Fig.33 shows the return loss. The red line is a measurement result. The blue line is a simulation result. Fig.31 Dipole antenna Fig.33 Return loss

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 1.478V Fig.34 shows the measured charging profile at the distance 0.8m. The transmitter antenna power is 27 dBm . The constant current is 260 uA. The charging voltage is 1.478V. The 3.96mF capacitor is used for measuring the charging profile Instead of the battery. End of charging voltage is 1.445V. As the distance is increased, the current is decreased. Fig.35 shows the fast charging current for different distance. 27 s Fig.34 Measured charging profile Fig.35 Constant current for different distance

1 Return to 1 encoding 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 A Demodulator output B This slide is the measured demodulator output signal. Transmitter output power is 27 dBm. The distance for a measurement is 1m. Fig.37 A shows ask modulated signal. A transponder antenna receives the modulated signal. A fter this, ASK demodulator demodulate the received signal. Fig.37 B shows the demodulator output data for arbitrary input data. The maximum communication without error bits. distance is 1.8m Fig.36 Block diagram for a communication Fig.37 Demodulator output data stream for arbitrary input data

1 Manchester encoded data Measured backscattering modulator Input data rate : 320Kbps Encoding : Manchester encoding Difference of high and low (Fig.39 B): 5 mV A B This slide shows the measured backscattering modulator. The Manchester encoded data is created by a pulse pattern generator. The data go into a backscattering modulator and the matching network of a transponder is changed. This caused the change of reflected power. A reader detects the difference of reflected power. Fig.39 B show the receiver antenna signal. The difference of high level and low level of a receiver antenna signal is 5 mV. Receiver antenna signal Fig.38 Block diagram for a communication Fig.39 Modulated signal by a transponder

Power transfer method (inductive coupling)
Distance of a Reader and a transponder : 4 mm Power amp output power : 27 dBm Receiver inductor Fig.40 shows the inductive coupling experiment setup. The setup is similar to em wave method. The difference is a receiver inductor, a transmitter inductor, transponder inductor. A receiver inductor detects the change of the coupling coefficient between a transmitter antenna and a transponder antenna. Transmitter inductor Transponder inductor Test board Fig.40 Inductive coupling measurement setup

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.42 transmitter inductor smith chart Fig.41 shows a reader inductor matching network and a fabricated reader inductor. In a inductive coupling method, the SRF of an inductor is important. If the frequency is higher than a SRF of inductor, the capacitance is dominated. So that, the size of a inductor is restricted by SRF. The SRF of fabricated is 1.3 GHz, the inductance is 56 nH at 900MHz. And the Q value is 90 at 900MHz. Inductive coupling method is associated with the magnetic field of inductor. In order to maximize the magnetic field of a inductor, the current of inductor is maximized. So, by the series connection of a capacitor and an inductor, the reader inductor is resonated at 900MHz. The current of a inductor is maximized. Fig.43 shows the return loss the series connection of a capacitor and an inductor. -29dB Fig.41 Reader inductor matching / Reader inductor Fig.43 Return loss

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.45 Transponder inductor smith chart The SRF of transponder inductor is 1.39 GHz, inductance is 32nH at the 900 MHz, the Q value is 83 at the 900MHz. Fig.44 shows the transponder inductor and conjugate matching network. In order to maximize the power transfer to integrated chip, the conjugate matching network is applied. Fig.46 shows the return loss. Fig.44 transponder inductor /conjugate matching network Fig.46 Return loss

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 1.457V Fig.47 shows the measured charging profile at the distance 6.5mm. The output power of a power amp is 27 dBm . The constant current is 260 uA. The charging voltage is 1.457V. The 3.96mF capacitor is used for measuring the charging profile Instead of the battery. End of charging voltage is 1.445V. As the distance is increased, the current is decreased. Fig.48 shows the constant current for different distance. 26 s Fig.47 Measured charging profile Fig.48 Constant current for different distance

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 1 Return to 1 encoding A B This slide is the measured demodulator output signal. The output power of a power amp is 27 dBm. The distance for a measurement is 4mm. Fig.50 A shows ask modulated signal. A transponder inductor receives the modulated signal. After this, ASK demodulator demodulate the received signal. Fig.50 B shows the demodulator output data for arbitrary input data. The maximum communication distance is 6.5mm without error bits. Demodulator output Fig.49 Block diagram for a communication Fig.50 Demodulator output data stream for arbitrary input data

1 Measured load modulator Input data rate : 320Kbps Manchester encoding The difference of high level and low level : 4 mV Manchester encoding A B This slide shows the measured Load modulator. The Manchester encoded data is created by a pulse pattern generator. The data go into a backscattering modulator and the matching network of a transponder is changed. This caused the change of a coupling coefficient. A reader detects the changed coupling coefficient between a transmitter inductor and a transponder inductor. This show the receiver inductor signal. Fig.52 B shows the enlargement of oscilloscope output signal Receiver inductor signal Fig.51 Block diagram for a communication Fig.52 modulated signal by a transponder

Comparisons of conventional circuits
This work Conventional [1] IEEE 2007 Conventional[2] JSSC 2006 Power transfer method Inductive coupling EM wave Frequency 900 MHz 4 MHz 950MHz Operating VDD 1.54 4.1 1.5 Charging voltage, current 1.457 V 260 uA 4.1 V 1.5 mA 1.478 V x Charging efficiency 4.48 % 73 % communication uplink, downlink Maximum comm. distance 6.5 mm 1.8 m 10 m Antenna dimension 5mm X 6 mm -PCB (FR4) 9mm (diameter) -Coil with ferrite core Dipole antenna - 160 mm The table shows the comparisons of conventional circuits. In a inductive coupling method, conventional work don’t contain the communication mode. This work can communicate between a reader and a transponder. Also, by using the UHF region, the inductor dimension is smaller than the conventional work and the inductor material is cheaper than the conventional work. In a EM wave method, conventional work don’t contain the charging circuit. This work contains the charging circuit. So, secondary battery is charged by the wireless power transfer. Also, when the inductive coupling method and the EM wave method is compared, the inductor dimension is greatly smaller than the dipole antenna. so that, inductive coupling method at the uhf region is suit for implanted medical devices. Table.2. Comparisons of conventional circuits

Conclusion 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) In implanted medical devices, Because the inductor antenna is used at the UHF, the transponder size can be small. The inductor dimension is 5mm X 6 mm Because the transponder battery is charged by the incident RF power, it can prevent regular surgery in the implanted medical device. And, due to the wireless communication, the reader receives the information from a body easily. The effect on a body is lower than EM wave method since the inductor antenna is operated by magnetic coupling

Reference [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

APPENDIX 1 Rectifier Rectifier sensitivity
Rectifier output voltage for the frequency Rectifier efficiency : 5.58 % (Load 10Kohm, Input power 3dBm) load 10Kohm 1.05 V 그림 5는 rectifier의 sensitivity를 나타냅니다. Rectifier 의 efficiency는 input power 3dBm에서 5.58%입니다. 그리고 그림 6은 주파수를 변경시켜 가면서 전압을 측정해 보았는데, 890MHz 에서 910MHz사이에서 최대 전력전송이 나타나는 것을 볼 수 있었고, 즉 carrier frequency인 900MHz에서 최대 전력전송이된다는 것을 의미 합니다. 3 dBm Fig.1 Measured rectifier sensitivity Fig.2 rectifier output voltage for different frequency

APPENDIX 2 Battery Charging Profile Silver Zinc rechargeable battery
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) Fig.3 Charging Profile

APPENDIX3 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 show the charging current for different input power. Fig.17 show EOC voltage for different input power. As the input power is decreased, EOC voltage is also decreased. If the EOC voltage is decreased, the battery is not charged perfectly. So that, the life time of a battery is decreased. Therefore minimum EOC voltage is batter 그리고 transponder가 받는 power양은 거리에 따라 달라지게 됩니다. 그렇게 되면 battery로 흘러 가는 전류의 양이 달라지게 되는데 그림 18은 input power을 변화 시켜 가면서 그에 따른 전류 양을 측정해 본결과 입니다. 또한 input power에 따라서 EOC voltage도 달라지게 되는데 그림 19는 input power에 따른 EOC voltage를 보여줍니다. Rechargeable battery에 충전이 될때 기준 전압보다 작게 충전되거나 혹인 많게 충전되게 되면 battery 수명이 짧아 지게 됩니다. Fig.16 Measured Charging current for different input power Fig.17 Measured EOC voltage for different input power

APPENDIX 4 Regulator schematic Fig.4 Regulator schematic

APPENDIX 5 Demodulator schematic Fig.5 Demodulator schematic

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

APPENDIX 7 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 1 이번 슬라이드는 Demodulator의 동작 결과 입니다. Direct input signal power는 6dBm 이고, Return to 1 encoding 방식이 적용된 arbitrary RF signal이 들어왔을때 output 결과 모습입니다. Data error 없이 잘 동작 하는 것을 확인 할 수 있었습니다. 그리고 designed demodulator의 sensitivity는 1.67dBm입니다. Fig.22 Block diagram for a communication Fig.23 Demodulator output data stream for arbitrary input data stream

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

APPENDIX 9 Available power Measurement of Rectifier output voltage
- Load 10 Kohm Antenna input power: 27 dBm (500 mW) : 625uW at the distance 1.05 m Fig.11 Available power measurement method Fig.12 Available power for different distance

APPENDIX 10 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.13 Available power measurement method Fig.14 Available power for different distance

APPENDIX 11 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 Modulator spectrum for 320 KHz with NRZ encoding
Fig.17 Backscattering modulator spectrum for 320 KHz NRZ encoding Fig.18 Load modulator spectrum for arbitrary 320 KHz NRZ encoding

Inductively coupled UHF RFID transponder for implanted medical devices

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Inductively coupled UHF RFID transponder for implanted medical devices

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