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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?



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

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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
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