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- A Design of Energy Harvesting System and Circuits - Joo-Heyn Park August 21, 2015 IC Lab., Sungkyunkwan University [email protected] http://iclab.skku.ac.kr Contents for Energy Harvesting System Introduction and Motivation Energy Harvesting Techniques RF Energy Harvesting System. Conventional RF Energy Harvesting System. An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With α-Calibrated Conclusion 2 Contents for Energy Harvesting System Introduction and Motivation Energy Harvesting Techniques RF Energy Harvesting System. Conventional RF Energy Harvesting System. An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With α-Calibrated Conclusion 3 Introduction What is the Energy Harvesting ? Energy harvesting or energy scavenging is a process that captures small amounts of energy that would otherwise be lost as heat, sound, vibration or RF Produce enough power to recharge the battery or directly supply the electronics Solve the problem that the devices is at inaccessible 4 Introduction 5 Contents for Energy Harvesting System Introduction and Motivation Energy Harvesting Techniques RF Energy Harvesting System. Conventional RF Energy Harvesting System. An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With α-Calibrated Conclusion 6 Energy Harvesting Common Energy Harvesting Source Mechanical Energy (PZT) - Vibration, stress Thermal Energy (TEG) - Furnaces, Heaters, Friction Light Energy (PV) - Photo-sensor, Photo-diode Electro-Magnetic (EM) -Inductors, Coils, Radio Freq. Natural Resources -Wind, Water, Solar, Human Other 7 Energy Harvesting When Does Harvesting Make Sens? Harvesting energy available Difficult to install or power devices Difficult to reach devices for maintenance Cords too costly Numerous devices Environmentally friendliness required High uptime demanded One or more these characteristics are required for energy harvesting to make sense compared to batteries 8 Energy Harvesting Energy Harvesting Tradeoffs Advantage • Mobile: no power wireless • Easier installation • Lower maintenance • Environmentally friendly • Higher uptime Disadvantage • Dependent on availability of harvestable energy source • Strict power budget • Upfront cost may be higher • Less mature technology 9 Energy Harvesting Key Functional requirements for Energy Harvesting Energy from ultra-low-voltage ambient energy sources Capture, Accumulate, Store and Manage Energy Produce usable Energy from low cost energy generators Perpetually internal self-powered self-starting circuitry High Energy Retention Always active in energy capture mode Output directly drive CMOS ICs, P, WSN, ZIGBEEs Outlasts system deployment lifetime Distributed energy sources enhances system reliability Virtually unlimited charge/discharge cycles 10 Energy Harvesting Pro. and Con. about Each energy source 11 Contents for Energy Harvesting System Introduction and Motivation Energy Harvesting Techniques RF Energy Harvesting System. Conventional RF Energy Harvesting System. An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With α-Calibrated Conclusion 12 Energy Harvesting RF Harvesting System Antenna RF Energy Matching Network Rectifier DC-DC Converter (Boost) Energy Storage Load RF Energy harvesting의 경우 공급 전력이 매우 작으므로, low-power circuits 설계가 필수 적임. Rectifier 의 출력 전압이 0.2 V ~ 1 V 로 낮게 생성될 수 있으므로, Boost converter를 이용하여 전압을 승압 하여 사용 함. 효율을 최대화 하기 위해 Matching Network를 통해 Rectifier와 안테나의 impedance matching을 최적화 해야 함. 필요에 따라 DC-DC Converter (Boost) 다음에 regulator 를 사용할 수 도 있음. 13 Energy Harvesting RF Energy Harvesting Process Wide-Band Antenna 500MHz ~ 2.4GHz Rectifier Output Voltage: 0.2~1.0V DC-DC Converter Transfer the original DC voltage (0.2~1.0V) to a higher usable level (e.g., 2V) Digital Controller Control the input impedance of DC-DC converter to deliver a maximum power to the output 14 Contents for Energy Harvesting System Introduction and Motivation Energy Harvesting Techniques RF Energy Harvesting System. Conventional RF Energy Harvesting System. An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With α-Calibrated Conclusion 15 RF Energy Harvesting System (2) [1] “An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm.” Ping-Hsuan Hsieh, Member, IEEE, Chih-Hsien Chou, and Tao Chiang. IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS, VOL. 62, NO. 6, JUNE 2015 < Top block diagram of RF energy-harvesting system > [1] An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm, IEEE, 2015 16 RF Energy Harvesting System (2) The proposed system feature 1). A single stage rectifier is adopted to prevent PCE degradation due to multi-stage architecture. 2). Switched inductor boost converter. 3). A low power control circuit that adopts a novel open loop asynchronous architecture. 4). Self start up circuit to kick-start the energy extraction process when the stored energy is low. The control block generates the control signals for switching activities and is supplied directly by the output voltage. In this design, the charging process is stopped as V(out) reaches 2V to prevent device breakdown and to emulate an over-voltage protection function. [1] An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm, IEEE, 2015 17 RF Energy Harvesting System (2) Full-bridge differential rectifier A full bridge differential rectifier that can achieve 80% PCE is used in this design. The loss of the rectifier mainly comes from the series loss which is a function of the loading condition and the switches on resistance. The PCE decreases once the input power become too large. This is due to the fact that the cross-coupled structure of NMOS and PMOS renders itself to reverse current. When the reverse current occurs, the signal voltage is large and the switches are on. However, the input AC amplitude is smaller than the output DC amplitude. This results in reverse current flowing V(dc) back to the source. To maximize the rectifier PCE as the input power level changes, we need to adjust the effective input impedance of the following boost converter. [1] An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm, IEEE, 2015 18 RF Energy Harvesting System (2) Matching Network In order to extract maximum power from the source, a matching network with simple shunt series inductor topology is adopted for impedance translation. The matching network also provides passive voltage amplification by converting low impedance of the source to high impedance of the circuit. [1] An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm, IEEE, 2015 19 RF Energy Harvesting System (2) Switched-Inductor Boost Converter A switched inductor boost converter is used to charge the output capacitance CL. It energizes the inductor first through the low-side (LS) switch for duration of T(LS) and then transfer the energy to V(out) during the second phase for T(HS) through the high side (HS) switch. The loss of the converter also comes from switches series loss [1] An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm, IEEE, 2015 20 RF Energy Harvesting System (2) Adaptive Control Circuit < Adaptive control (a) circuit (b) timing diagram > The novel open loop asynchronous control scheme consumes little power and optimizes the end to end PCE(harvester) by careful handling of the interface impedances between blocks and the control timing of operations. [1] An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm, IEEE, 2015 21 RF Energy Harvesting System (2) Startup and Reference Generator HS switch When the system is highly depleted, the output capacitor CL can be charged directly from input through rectifier and body diode of the HS switch to an opencircuit voltage. To kick-start the system operation, a low voltage ring oscillator is designed that can oscillate with supply voltage as low as 0.3 V. The start-up is disabled and the adaptive control circuit takes over once V(out) reaches 1 V. Band-gap circuit is used for reference generation. The simulated power consumption of the reference circuit is 1.5 uW at V(out) of 2 V. < Startup and reference generator circuit > [1] An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm, IEEE, 2015 22 Contents for Energy Harvesting System Introduction and Motivation Energy Harvesting Techniques RF Energy Harvesting System. Conventional RF Energy Harvesting System. An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With α-Calibrated Conclusion 23 RF Energy Harvesting System (4) [2] “A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With -Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control.” by Tzu-Chi Huang, Student Member, IEEE, Chun-Yu Hsieh, Yao-Yi Yang, Student Member, IEEE, Yu Huei Lee, Student Member, IEEE, Yu Chai Kang, Ke Horng Chen, Senior Member, IEEE, Chen Chih Huang, Ying-Hsi Lin, and Ming-Wei Lee. IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 47, NO. 4, APRIL 2012 Each patient wears several sensor nodes responsible for specific physiological signals in several small monitoring systems. Through wireless communication, the central health server can collect the sensed data. < Wireless bio-sensor network > Each sensor node works as a micro system that has to be sustained for a long time because of the inconvenience of changing the battery. [2] A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With -Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control, JSSC, 2012 24 RF Energy Harvesting System (4) Structure of energy harvesting circuit The coupling inductor or antenna followed by a voltage doubler receives external RF power from the power amplifier to charge capacitor Cin. The Buck converter transfer energy from Cin to the out put capacitor Cout to derive the system. For high performance operation, the driving voltage is regulated at 1 V, which is equal to the reference voltage. Low bias current is known to result in slow response and propagation delay in analog circuits, thus post-regulator such as LDO regulator is required but LDO consumes great power and large silicon area so we use an APLcomparator to improve the response time and load regulation. [2] A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With -Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control, JSSC, 2012 25 RF Energy Harvesting System (4) Structure of energy harvesting circuit The DOOT controller generate the on-time and off-time periods to control the power (MOSFETs) Mp1 and Mn1. A high-precision and fastresponse comparator is required to rapidly switch off the power MOSFET when the inductor current reaches zero. Driving current increase in comparator because of conventional converter design methodology, but it consumes large power, so for reducing power consumption a digital calibration circuit is implemented. The digital calibration scheme will be shut-down to further decrease power consumption when the harvesting system is in normal operation. The entire harvesting system is deliberately designed for power reduction and improving accuracy in each control module. [2] A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With -Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control, JSSC, 2012 26 RF Energy Harvesting System (4) Nano-Power Bias Circuit < Nano-power Biasing current and reference voltage generator > This figure the nano-power biasing current and voltage generator in the DOOT controller. The reference voltage is generated at 1V, which is equal to VOUT, and a nano-ampere biasing current can be implemented. [2] A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With -Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control, JSSC, 2012 27 RF Energy Harvesting System (4) Proposed summary [2] A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With -Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control, JSSC, 2012 28 Contents for Energy Harvesting System Introduction and Motivation Energy Harvesting Techniques RF Energy Harvesting System. Conventional RF Energy Harvesting System. An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With α-Calibrated Conclusion 29 Conclusion Proposed summary 30 References [1] Ping-Hsuan Hsieh, Chih-Hsien Chou, and Tao Chiang, “An RF Energy Harvester With 44.1% PCE at Input Available Power of -12 dBm”, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS, VOL. 62, NO. 6, JUNE 2015 [2] Tzu-Chi Huang, Chun-Yu Hsieh, Yao-Yi Yang, Yu Huei Lee, Yu Chai Kang, Ke Horng Chen, Chen Chih Huang, Ying-Hsi Lin, and Ming-Wei Lee, “A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With α-Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control”, IEEE JOURNAL OF SOLIDSTATE CIRCUITS, VOL. 47, NO. 4, APRIL 2012 31 Thank you !!! Q&A 32