1. Design of Power Management for
Autonomous Wireless Monitoring
Systems
Master Thesis Presentation
By
Mayur Sarode
Supervisors
TU/e : P.G.M Baltus, Dusan Milosevic
imec/Holst center :Valer Pop

2. RF ENERGY HARVESTING
RF-DC DC-DC Energy
PM
converter converter
circuit
Storage WATS
Device
RECTENNA
Horn antenna DC-DC converter e.g. EOG tracking
Microstrip patch based
antenna , Ni-MH battery Eye system
Diode based voltage
doubler
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3. PROJECT OUTLINE
MOTIVATION
STATE-OF-THE-ART-PM*
HARVESTER
MEASUREMENTS
PM CIRCUIT DESIGN
PM CIRCUIT
MEASUREMENTS
RECOMMENDATIONS &
CONCLUSIONS
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4. MOTIVATION
Architectural level: Multi supply  one-voltage domain system
9% 22%
<1% 11% Radio
<1% MCU
PM 63μW PM 33μW
31% 39%
(704 μW) ADC (151μW)
Sensor&R-out 1%
78% PM 4%
Vdd[V] Component Vdd [V]
3 Radio 1.2
2.3 MCU 1.2
2.7 ADC 1.2
3 Sensor & R-out 1.2
2.9 Battery 1.5
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5. STATE-OF-THE-ART OF PM
Inductive vs Capacitive Converter topology
PWM/PFM control strategy
Size
Efficiency
Quiescent current
Start-up voltage
Converter specs Io(max),Vdc(max), fs and Vbatt
Open-loop resistor –emulation optimum control strategy
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6. STATE-OF-THE-ART PM ; IMEC/HOLST CENTER
AC-DC buck-converter Inductive boost- converter Integrated capacitive DC-DC
buck-boost converter
Specifications
Specifications Specifications ▸ Input voltage 1~5VDC
▸ Integrated AC-DC rectifier ▸ Adaptive MPP Control ▸ Output 10~300 μW
▸ Input voltage 4~42VRMS ▸ Input voltage 1~2VDC ▸ Active Efficiency 80~87%
▸ Output 10μW~5mW @ 3VDC ▸ Output 10μW~5mW & up to100% in direct charge
▸ DC-DC Efficiency 87 - 94% ▸ End to end efficiency 60~70%
Technology
Technology Technology ▸ Indoor Photo Voltaic
▸ Vibrational Harvesting ▸ Indoor Photo Voltaic
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7. HARVESTER MEASUREMENTS; CHARACTERIZATION
Harvester characterization  Power management specifications
Parameter Value Unit
Load No load, 10, 100, 10K, 100K Ω
Rectenna
Transmitted power 0 ,14 ,20 dBm
Distance 1, 10, 20, 30, 50 cm
Height 10 cm
Orientation of Broadside /Vertical
Rectenna
Configuration Line of Sight, 45o ------
Rectifier
Pinc -15 to 10 dBm
 Find optimum load resistance
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8. HARVESTER MEASUREMENTS; RESULTS
Parameter Value (EIRP: 100 mW) Unit
Distance , R 1 10 20 30 50 cm
Voltage , Vdc 1.2 0.6 0.3 0.2 0.12 mV
Power, Pdc 1886 292.6 82 44 15 μW
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9. HARVESTER MEASUREMENTS; LOSSES
Impedance matching losses ZL [Ω] Г
ZS [Ω] Pinc [dBm]
2
Z L Z s*  35+40j Ω
-15
0
2.5-55j Ω
35-40 j Ω
0.78
0
Z L Zs
ZL - Load Impedance
ZS – Source Impedance
 Rectenna efficiency  varies with available power
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10. HARVESTER MEASUREMENTS; CONCLUSIONS
Rectenna A Rectenna B
Input power to the converter < 500 μW
Maximum input voltage to converter Vdc(max) ~ 0.4 V
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11. HARVESTER MEASUREMENTS; CONCLUSIONS
Rectenna A Rectenna B
Optimum load resistance varies with input power MPPT
Approximated to a constant resistance (Rdc) for resistor emulation
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12. HARVESTER MEASUREMENTS;DERIVED SPECS.
Parameter Value/ Functionality Unit
Harvester
Distance 0.2 – 0.6 m
Rectenna Broadside in LOS* ---
EIRP (max) 4 W, 50% Duty Cycled W
Power management Circuit
Input voltage Vdc 0.1 – 0.5 V
Output voltage Vbatt Dependent on the battery (~1) V
Input impedance Rdc 220 (reconfigurable) Ω
Input power Pdc 1 - 500 μW
Choice of a lower Rdc rectenna for resistor emulation
 Choice of optimum PM circuit components *LOS- Line of Sight
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13. RF MEASUREMENTS; RECTENNA MODELING
 Friis model Rectifier measurements
Parameter Value Unit
PT 0.004 – 1.24 W
GT 3.2 ---
GR 3.1 ---
λ 0.1244 m
R 0.16 – 0.60 m
PT(14dBm) ~ EIRP(80.64 mW)
Based on Spline interpolation
GT – Gain of the transmitter antenna
GR – Gain of the receiver antenna
Used for predicting autonomy λ – wavelength
R - Distance from the transmitter
EIRP - Effective Isotropic Radiated Power
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14. PM CIRCUIT DESIGN; DEFINING VARIABLES
Harvester Terminology
Variable Details
Pin( Vin) Incident power(voltage)on the rectenna
Pdc(Vdc) Input power(Input voltage) to the
converter
Pout Harvested Power
ηconverter (Pout/Pdc)
ηharvester (Pout/Pin)
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15. PM CIRCUIT DESIGN; SPECIFICATIONS
Specifications Comments Unit
Input impedance (Rdc) 220 (rectenna B) Ω
Switching frequency, fs ----- kHz
Input voltage, Vdc 0.1 - 1 V
Output voltage, Vbatt 1 – 1.3 V
Output current , Io(max) 1 mA
Under Lock-out voltage ----- V
Over lock-out voltage 1.3 V
Input Ripple voltage 20% Vdc V
output Ripple voltage ,ΔVo 1 mV
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16. PM CIRCUIT DESIGN; POWER STAGE
ton D
M1
Vdc
Rdc
RECTENNA
Ds RL
Rin
Cin Cout
Ls
Vin Vbatt
Buck-Boost converter topology
D
Relating input/output voltage Vbatt Vdc
2 Ls
RLTs
On-time is calculated by 2 Ls
ton
f s Rdc
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17. PM CIRCUIT DESIGN; SELECTION OF M1
MOSFET power loss modeling
MODELED MEASURED
Choice dependant on Ron , tr , tf and Cgs of the MOSFET
Verified with measurement results
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18. PM CIRCUIT DESIGN; SELECTION OF Ds
Schottky Diode forward voltage drop (Vf )
& Continuous Reverse Current( Is)
Power losses at Vin 0.3 V (model)
Verified with SPICE simulations
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19. PM CIRCUIT DESIGN; SELECTION OF Ls
Conduction losses  DCR
Trade off between inductor and diode conduction time
80
COnverter Efficiency [%]
70
60
50 900uW
180uW
100uW
40
1000
1500
1800
2200
220
68
 Sweeping Ls for Rdc of 220Ω
Inductance [μH]
 Ls between 1 – 1.5mH is optimal
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20. PM CIRCUIT DESIGN; SELECTION OF Cin
Cin  Reduce ripple voltage
BEFORE AFTER
Input capacitance was selected to be 10 μF(ESR 5 mΩ)
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21. PM CIRCUIT DESIGN; SELECTION OF COUT
Cout  Charge battery when M1 is ON
 Reduce output voltage ripple
BEFORE AFTER
 10μF low ESR selected
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22. PM CIRCUIT DESIGN; SELECTION OF fS
 Selected for minimum converter loss
 Optimum switching frequency increases with input power
 PWM designed to reduce losses at low input power levels
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23. PM CIRCUIT DESIGN; OSCILLATOR DESIGN
RC relaxation oscillator Low voltage comparator
Vdd, Vss
R2
R1
+
-
R3 D1 D2
Rh
Rl
Cosc
Vdc Observed oscillation frequency at Vin :0.9 volt
Duty cycle scales with step-up ratio
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24. PM CIRCUIT DESIGN; PROTECTION CIRUCIT
Overcharging protection MAX9064
Under lock out protection MAX9063
Vbatt
Vref
Vdc
Vref
R10
- R7
Vin2 +
R8 V1
Comp_U Comp_H V2
+ Dc
Vin1 -
R6
R9
Vbatt
Under-lock out  150 mV , Vdc
Over-charging protection  1.3 V, Vbatt
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25. PM CIRCUIT DESIGN; LOSS ANALYSIS
Modeling Converter losses at different power levels
250
Ploss [μW]
Leakge
Oscillator
200 Switch
Diode
Inductor
150
100
50
0
102 410.58 924
Diode major contributor Pin [μW]
Leakage losses dominate at lower power levels
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26. PM CIRCUIT DESIGN; HARDWARE DEVELOPMENT
PCB
testing
Layout  Expedition
PCB tool*
Schematic Design Capture tool*
Circuit Verification on Breadboard
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27. PM MEASUREMENTS
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28. PM MEASUREMENT; RESULTS
Comparing Efficiency present & new generation PM
Efficiency and output power for Vbatt 1.030 and 3.5 volt for 220 Ω rectenna
Higher efficiency at lower rectenna voltages Vin
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29. PM MEASUREMENTS; WITH RECTENNA
Comparing Autonomy
80 80
Efficiency [%]
Efficiency [%]
10 cm 20 cm Present generation
New generation
60 60
40 40
20 20
0 0
converter harvester converter harvester
Measured efficiency at distance of 10 and 20 cm
Increase in Autonomy of the harvester EIRP:100 mW
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30. PM MEASUREMENT; RESULTS
Start-up voltage varies with battery voltage
Start-up voltage of 210 mV Vin for Vbatt of 1.03 volt
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31. PM CIRCUIT ; OVERVIEW
DCM, non synchronous buck-boost converter
Over-Charging protection / under lockout protection
Quiescent current of 27 μA
Compact Design (2X2 cm 2 layer PCB board )
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32. RECOMMENDATIONS
TPS22902 load switch, Ron 146 mΩ
Quiescent Current Distribution
Reducing Quiescent current at under-lockout voltage levels
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33. RECOMMENDATIONS
 Higher ηconverter  PWM-PFM control strategy
Higher ηconverter with adaptive PWM
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34. SUMMARY
 1 V battery charging  lowest among commercial solutions
ηconverter ~ 68% @ 900 mV available voltage
Start-up voltage ~ 0.210 V
Quiescent current ~~ 1 V IC solutions
Protection circuits
Reconfigurable for any arbitrary rectenna ( Rmpp 800Ω, 2.6 kΩ)
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35. THANKS ….
Valer Pop , Prof. Peter Baltus , Dusan Milosevic
My family and friends
Audience present today
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36. CIRCUIT VERIFICATION
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37. WATS ARCHITECTURE
Application electronics
Sensor ADC Processor Radio
Power transfer DC-DC
converter
Data transfer
Energy storage
RF-DC DC-DC
converter converter - Battery
- Super capacitor
Rectenna PM
Energy Harvester
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38. SCHEMATIC DESIGN
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39. LAYOUT
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40. PCB TESTING
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