powering the internet of things · trends in low-power electronics 2 . iot node for monitoring...
TRANSCRIPT
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Powering the internet of
things
Yogesh Ramadass
Texas Instruments
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• Issues - Size, weight, operating lifetime
• Energy efficiency of IC’s is crucial
Increasing Energy Criticality
Implantables
Sensor Networks Handhelds
Portable
Computers
Wearable Devices
Trends in low-power electronics
2
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IoT Node for Monitoring
Component Power Comments
Inst. Amplifier
[Verma,
VLSI09]
3.5µW
1V VDD,
1.3µVrms input
referred noise
ADC
[Yaul,
ISSCC14]
3.7µW
1V VDD, 450kS/s,
9.8ENOB
16b µ-cont
[Kwong,
ISSCC08]
2.72µW 0.5V VDD,128kb
SRAM, 100kHz
Radio
[CC 2550]
33.6mW
(active)
3V VDD, 2.4GHz,
-12dBm POUT
• Power consumption of building blocks steadily decreasing
• Low voltage operation, multi-cores, local processing of information, aggressive duty cycling
3
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LSB-first SAR ADC for Low-Activity Signals
0 1000 2000 3000 4000 0
512
1024
Outp
ut
Code
Sample Number
αAccel = 6.7%
0 1000 2000 3000 256
512
768
Outp
ut
Code
Sample Number
αECG = 0.6%
Range
ECG Signal, 1 kS/s Vibration Signal, 5 kS/s
Range is given for best case
(DC) and worst case (fullscale
Nyquist sinusoid) inputs.
[F. Yaul, ISSCC 2014]
LSB-first predictive algorithm for reduced power
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Reduced radio consumption
On-scalp Field Potentials (EEG):
Clinical
onset
Electrical
onset
~7.5sec
Computation vs. Communication Trade-off
Conventional-
Wireless EEG
Using Local
Processing
Capture 75 μW 75 μW
Digital processing -- 2 μW
Radio 1733 μW 43 μW
Total 1808 μW 120 μW
[N. Verma, VLSI Circuits Symposium 2009]
Epileptic Seizure Onset Detection
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Hard to
Reach
Convenience
Electronic Shelf
Labels Solar Keyboard
Environmental Awareness
Pipelines Oil Rig
Occupancy
Sensor
Self-Powered Applications
Smoke
Detector
Low data rate, low duty cycle, ultra-low power
6
Self-powered
switches
Structural
sensors
Implantables
TPMS
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Outline
• Energy Sources and Characteristics Energy Harvesting System
Solar
Thermal
Vibration
• Energy Storage Options
• Energy Management Circuits Chargers
DC/DC Converters
Battery Management
Peripherals
• Summary
7
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Battery Operated System
• Battery is an energy source
• System needs to be ON only when the load demands it
Self-powered solutions desirable
1cm3 Li-ion 2800J 1year at 100μW
Battery
Management
(UV, OT)
Power good
indicator
RegulatorBattery
AFE
Radio
MicroProc.
Sensor
8
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Energy Harvesting System
9
Energy harvesters are power sources
Boost
Charger
Cold
Start
Battery
Management
(OV, UV, OT)
Power good
indicatorMPPT
RegulatorSolar /
Thermal
Harvester
AFE
Radio
MicroProc.
Sensor
Battery /
Supercap
Rectifier
Vibration
Harvester /
Targeted
RF
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Harvesting Light Energy
*US Department of Energy
• Incident light generates electron-hole pairs
• ISC proportional to light intensity
10
ISC CCELL
RS
RP
VCELL
ICELL
_
+
Conditions Power density
Indoor 10µW/cm2
Outdoor 10mW/cm2
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Common Solar Cell Types
Crystalline
Amorphous
Dye-Sensitized
(DSSC)
[Sinonar] [IXYS]
[G24i] [SolarPrint]
[Sanyo] [EnOcean]
11
M. Gratzel, “Photovoltaic and photoelectrochemical conversion of solar energy,”
Philosophical Trans. Royal Society A, 2007
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Output power curves with light intensity
12
Increasing
Intensity
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• One p-n leg generates ~ 0.2mV/K
• Open-circuit voltage proportional to temperature difference across TEG
Thermoelectric Energy Harvesters
13
Conditions Power density
Wearable 60µW/cm2
Industrial 5mW/cm2
Lim, Nasa Tech Briefs, 2008
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TEG Characteristics
• Tellurex G1-1.0-127-1.27
• S = 23mV/K; RT = 5Ω
[Tellurex]
14
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TEG Characteristics
• Micropelt MPG-D751
• S = 155mV/K; RT = 300Ω
15
[Micropelt]
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Body Heat Powered Electronics
System Concept Thermo-Electric Devices
Thermal Energy Chip
For low-power wearable electronics
[Y. Ramadass and A. Chandrakasan, ISSCC 2010]
IMEC Tellurex Micro-pelt
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Mechanical Vibration Harvesters
[Perpetuum] [FerroSolutions]
FerroSolutions VEH-460 17
Conditions Power density
Wearable 4µW/cm3
Industrial 1mW/cm3
[Mide Volture v22b]
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Vibration-to-Electric Energy
Piezoelectric
Micro-Power
Generators
10µW -100µW generated
Sang-Gook Kim (MIT)
RECTIFIER
BUCK BOOST
ARBITER
RECTIFIER
BUCK BOOST
ARBITER
Vibrations Power Distributed Sensor Devices
(Battery-less Operation)
Self-powered Wireless
Corrosion Monitoring
Sensors Power Converter
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e-Textiles with Wireless Power/Data Transfer
Nachiket Desai, ISSCC 2013 Conditions Power density
Near field 5mW/cm2
Far field <10µW/cm2
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Boost
Charger
Cold
Start
Battery
Management
(OV, UV, OT)
Power good
indicatorMPPT
RegulatorSolar /
Thermal
Harvester
AFE
Radio
MicroProc.
Sensor
Battery /
Supercap
Rectifier
Vibration
Harvester /
Targeted
RF
Energy Storage Options
20
Store extracted energy from harvesters and
provide to load
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Energy Buffer
21
• Accumulate input power
• Provide peak output power
• Smooth out input, output power imbalances
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Energy Storage Options
Conventional
Batteries
Recharge Cycles 100s
Self Discharge Moderate
Charge Time Hours
Impedance Low - High
Physical Size Large
Capacity 0.3-2500mAH
22
• NiCd, NiMH, Li chemistries
• AA, AAA batteries have high capacity, low internal impedance, higher self discharge
• Li coin cells have low capacity, high internal impedance, smaller form factor
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Energy Storage Options
Conventional
Batteries
Thin Film
Batteries
Recharge Cycles 100s 5k-10k
Self Discharge Moderate Negligible
Charge Time Hours Minutes
Impedance Low - High High
Physical Size Large Small
Capacity 0.3-2500mAH 12-2200µAH
23
• Solid-state LiPON electrolyte
• Higher output currents compared to coin cells
• Extremely low self-discharge
• Variety of form factors, intrinsically safe, high temp.
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Energy Storage Options
Conventional
Batteries
Thin Film
Batteries Supercaps
Recharge Cycles 100s 5k-10k Millions
Self Discharge Moderate Negligible High
Charge Time Hours Minutes Sec-Minutes
Impedance Low - High High Low
Physical Size Large Small Medium
Capacity 0.3-2500mAH 12-2200µAH 10-100µAH
24
• Supports high peak output currents
• Very high leakage currents
• Wide range of operating temperature
[AVX]
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Duty Cycle Impact on Current
25
Active current
dominant
Sleep current
dominant
)1(**)( DIsleepDIactiveavgI
Interval Activity
Width PulseD
Pulse Width = 50ms
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Energy Processor
Take input energy from harvester and charge the
storage element efficiently 26
Boost
Charger
Cold
Start
Battery
Management
(OV, UV, OT)
Power good
indicatorMPPT
RegulatorSolar /
Thermal
Harvester
AFE
Radio
MicroProc.
Sensor
Battery /
Supercap
Rectifier
Vibration
Harvester /
Targeted
RF
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VSS
LBUCK 10.0HL2
Buck
Controller
Host
GPIO1
GPIO2 VOUT_EN
22FCOUT
/ENV
RD
IV
OK
_H
YS
RVO1
RVO2V
OU
T_
SE
T
OUT
GPIO2 VBAT_OK
Nano-Power
Management
VBAT
+BAT
VSTOR
+CSTOR
LBOOST
Boost
Controller
VSS
22H
L1
4.7F
VIN_DC
Solar
Cell
+
-
Cold Start
OK
_P
RO
G
ROK1
ROK2
ROK3
RVO1
RVO2
VB
AT
_O
V
VBAT
System
Load
VSTOR
bq25570
10nF
VREF_SAMP
MPPT
VOC_SAMP
High efficiency
boost charger
with MPPT
Custom programmability for
battery OV, battery OK, and
buck output regulation.
100mV to 4V VIN
with cold-start
circuit
Harvester
Storage
(2.0 – 5.5V)
Prog. between
1.3V and 5V
Energy Mgmt. IC -BQ25570
Quiescent
Current = 480nA
http://www.ti.com/product/bq25570
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BQ25570 Charger Architecture
VSTOR
LBST
HS_ON
CSTOR
HS_ON
CS2
CS1
DIGITAL
LOGICDRIVERS
LS_ON
DELAY
COMP1
HS_ON
COMP2
VSTOR
OV_REF
VREF
VIN_DC
OCV
DETECT
VIN_DC
CS1 CS2
STOP_HS
OV
OCV_EN CHARGER_EN
DELAYLS_ON STOP_LS
VIN_DC
• Synchronous boost converter with input regulation
• 80mV – 4V input voltage
• 10µA – 100mA input current 28
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BQ25570 Charger Efficiency • Single cell solar operation in indoor light (200 lux)
• Harvesting from thermoelectric generators
Eff Vs Iin
• 35% efficiency with 10µA input at 0.5V
• > 80% above 100µA.
Eff Vs Vin
• 38% efficiency with 100mV input at 10mA
• >80% above 0.5V 29
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Revisiting solar MPP curves
30 Output power levels within 0.5%
MPP
0.73(OCV)
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BQ25570 Maximum Power Point Tracking
• Open circuit voltage based MPPT
• Charger periodically turned off using EN signal
• IC samples and holds fraction of OCV on external capacitor
• Charger regulates input to value held on capacitor
Solar TEG
MPPT fraction
~75% 50%
256ms
16s
EN
VIN_DCCharger
CREF
ENR1
R2
ENZ
This work
31
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32
Maximum Power Point Tracking Input Open Circuit
Voltage (OCV)
Input Voltage
(VIN)
1V
2V
16s 16s
0.8V
1.6V
0.8V
1V Charger
regulates
VIN to 80%
of OCV
Periodic
sampling of
OCV
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• Function : Start system with depleted storage
• Architecture : Input powered boost converter
330mV Cold Start
Enable
Switch
33 K. Kadirvel, ISSCC, 2012
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Regulator
Present stored energy as a regulated supply to
load circuits 34
Boost
Charger
Cold
Start
Battery
Management
(OV, UV, OT)
Power good
indicatorMPPT
RegulatorSolar /
Thermal
Harvester
AFE
Radio
MicroProc.
Sensor
Battery /
Supercap
Rectifier
Vibration
Harvester /
Targeted
RF
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35
DC-DC Converter Topologies
• Linear loss in efficiency • Compact and easy to control
Linear (LDO) Regulators
Fully integrated
High efficiency X
Voltage Scalability
COUT
AMP
VREF
VIN
VOUT
IN
OUT
V
V
M. Al-Shyoukh et al., “A Transient Enhanced Low-Quiescent Current Low-Dropout Regulator
with Buffer Impedance Attenuation” IEEE JSSC, Aug 2007
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36
DC-DC Converter Topologies
• Maintaining efficiency across load voltages is difficult
• Output current capability is limited
Linear (LDO) Regulators
Switched Capacitor
Converters
Fully integrated
High efficiency X
Voltage Scalability X
VOUT
VIN
C
Φ1 Φ2
Φ2 Φ1
1) Y. Ramadass et al., “A 0.16mm2 Completely On-Chip Switched-Capacitor DC-DC Converter
Using Digital Capacitance Modulation for LDO Replacement in 45nm CMOS ,” IEEE ISSSC, 2010
2) Michael Seeman et al., “A Comparative Analysis of Switched-Capacitor and Inductor-Based DC-
DC Conversion Technologies,” Control and Modeling for Power Electronics, 2010
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0.2 0.4 0.6 0.8 1 1.2
10-3
10-2
10-1
100
E/c
yc o
f A
LU
(p
J)
VDD
(V)
Subthreshold MSP430 Microcontroller
ELEAK = ILEAKVDDdt ∫
EACT=CVDD2
ETOT
Sub-Vt 16b
μ-controller
Programmable
switched-capacitor
DC-DC
Sub-Vt
8T SRAM
1.2V
0.6V 0.3V
2.29mm
128Kb SRAM
array
DC-DC
converter
Core logic
(2 power domains)
1.8
6m
m
1 10 100 5000.5
0.55
0.6
0.65
0.7
0.75
0.8
Load Power (W)
Eff
icie
ncy
Joyce Kwong et. al, ISSCC 2008
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38
DC-DC Converter Topologies
• Needs an external inductor • Can achieve very high
efficiency • Wide range of output
voltages
Linear (LDO) Regulators
Switched Capacitor
Converters
Inductor-based Switching
Converters
Fully integrated X
High efficiency X
Voltage Scalability X
VOUT
LDIGITAL
CONTROL
VIN
VREF
COUT
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• Input voltage: 2V – 5.5V
• Output programmable between 1.3V – 5.25V
• Up to 50mA load current
TPS62736 Buck Converter Architecture
39
http://www.ti.com/product/tps62736
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TPS62736 Buck Converter Efficiency
• Maintains constant efficiency from 20µA to 50mA
• >80% down to 10µA
• IQ = 360nA
40
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Battery Management and Peripherals
41
Boost
Charger
Cold
Start
Battery
Management
(OV, UV, OT)
Power good
indicatorMPPT
RegulatorSolar /
Thermal
Harvester
AFE
Radio
MicroProc.
Sensor
Battery /
Supercap
Rectifier
Vibration
Harvester /
Targeted
RF
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BQ25570 Essential Peripheral Circuits
42
CHG_EN
BGP_EN
POR / Bias
Current
Generator2kHz
Osc.
POR CLK
State
Machine BattMgmt_EN
MPPT_CLK
Bias Currents
BandgapOT
BGP
Battery
Manager
UV
OV
VBAT_OK
VOUT_REF
BUCK_ENUV
OV
VBAT_OK
OT
Protect the storage element, manage the IC and
indicate level of stored energy
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R5
+
-
R4
R3
+
-R7
R6
Rh
VSTOR
+
-
UZ
1.25VR1
R2
KZ
UV
OK1.25V
1.25VC1
C2
C3
ENZ
OVSZ
OVS
OVSOVS
EN
EN
OV_REF
Under Voltage Battery OK
Over voltage
43
Battery Mgmt. Architecture
EN
OVS
• Resistor programmable UV, OK, OV
• Cycle repeats every 64ms
• Duty cycled and sampled reference
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BQ25570 Quiescent Current
• VBAT = 3V
• Overall Quiescent current : 480nA
• Battery leakage below UV = 1nA
Currents in nA 44
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BQ25570 System Startup
VSTOR
VBAT_OK
VBAT
VIN = 330mV
Switch between
VSTOR and VBAT
closes at UV
Open circuit
voltage sampling
for MPPT Cold Start Charger On OV
Battery at
OV = 3.3V
Battery OK
goes high
45
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Computing Architecture with Energy Harvesting
• Rapid transition from sleep to active
[M. Qazi, ISSCC 2013]
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Energy Harvesting with Battery Backup
http://www.ti.com/product/bq25505
Autonomous handoff between primary and secondary storage
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Energy Combining and Inductor Sharing
• A single inductor is shared between multiple harvesters
and output voltage regulators
S. Bandyopadhyay, [VLSI Symposium 2013]
A. Shrivastava, [VLSI Symposium 2014]
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Indoor Light Harvesting for Bluetooth LE (BLE) Beacons
Required Energy Budget Calculation
Solar cell provides 400µW
at 450Lux
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50
Summary
• Advances in circuit design techniques and architectures have made it possible for electronic systems to be completely self-powered
• Energy harvesting sources differ in characteristics from conventional batteries requiring specialized interface circuits
• Optimized energy processing circuits are crucial to manage the ultra-low power levels output by energy harvesters
• Holistic optimization of the complete system from the energy sources to the load circuits is key to building and powering a successful IoT system