IN5260 / IN9260 Low Power IoT Nodes, April 14th, 2021
Power and energy limitations related to Energy Harvesting and
requirements enabling IoT penetration.
Some building block-, system examples and trends .
Modulation, RF transceivers and receivers
Last, Wednesday 7th of April
• Briefly about some of the most common principles for energy harvesting for IoT
nodes
• Energy harvesting system example for a battery-less IoT-node
• Examples regarding physical size of batteries and how long different systems could
run just from the battery, without energy harvesting
• Examples of different energy harvesters and their typical power as a function of size
• RF harvesters and power, distance and frequency
• Energy harvesters and output voltage
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Energy harvesters; power, output voltage and average power
consumption for different electronic systems
• https://www.designnews.com/iot/energy-harvesting-low-power-consumption-are-way-forward-iot-wearables14.04.2021 3
Energy-Harvesting IoT – replacing the battery by energy harvesting
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WSNs have total power consumption well below 1 mW, and typically
communicate over maximum 10 meter distance, in a multi-hop fashion –
Not the only way!
• ASIC
• Hop-by-hop
• Max 10 m between nodes
• Above 10 m, transmitting
power gets excessive
• Roundy, Shad, Paul Kenneth Wright, and Jan M. Rabaey. "Energy scavenging for
wireless sensor networks." In Norwell, pp. 45-47. 2003.
14.04.2021 5
Some topics for Wednesday 14th of April
• Energy harvesting (EH) as enabler of the expansion of the IoT, provided
that power- and energy consumption may be radically reduced.
• COTS components that may be used for Self Powered Systems
• Full custom components that may be used in Self Powered Systems
• Trends for PMUs and «load» circuitry (the functionality served by the
PMU)
• Protocols and their usefulness for Ultra Low Power
• Some SPS component examples (body sensor node, PMU, analog front
end)
• Communication systems and RF
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Predictions regarding the global number of IoT devices have
been reduced, and a big part of the problem is the batteries
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The number of nodes in the IoT prohibits batteries
14.04.2021 8Benton Calhoun - Self Powered System Design for Next Generation Wireless Sensors
14.04.2021 9Benton Calhoun - Self Powered System Design for Next Generation Wireless Sensors
EH is the answer, but for the tiny IoT nodes 100x to 1000 x
improvement in power reduction is typically required
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Example view of a Self Powered System (SPS) Node
• Harvesting: converting ambient energy to usable energy
• Storage: holding charge for later use (capacitor, supercapacitor
and/or maybe a battery)
• Load circuits and regulation: do what needs doing, and must be
highly optimized
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Benton Calhoun - Self Powered System Design for Next Generation Wireless Sensors
https://everactive.com/videos/
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Some commercial off the shelf components (COTS) are
already feasible in Self Powered System (SPS) Nodes
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Benton Calhoun - Self Powered System Design for Next Generation Wireless Sensors
Benton Calhoun - Self Powered System Design for Next Generation Wireless Sensors
Sub-μW full custom components developed at the University
of Virginia, USA, around prof. Benton Calhoun
14.04.2021 14
Power trends for loads
• Power consumption
gradually decreases from
μW and nW, to pW during
about a decade
• This power scaling trend
slows down at pW level
• Based on figures from
ISSCC (B. Calhoun)
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Quiescent power trends of EH-Power Management Units
(PMUs) – down to nW and pW
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SPS design: Always on – wakeup receivers
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Ex. 6.45 μW Body sensor node with battery-free energy
harvesting and radio
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Activity detection
Fall detection
Temperature tracking
Heart rate monitoring
Fibrillation detection
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-Solar and thermoel. E. H.
-Radio
-Analog frontend for commercial
sensor compatibility
-OpenMSP430 processor
-Accelerators for biomed- and
environmental algorithms
-Control unit for management
when processor is off
-0.5 V for dig. (subthreshold)
6.45 μW
• 100 uA from indoor
solar
• Boost converter
can take Vin down
to 10 mV
• The SoC supports
numerous IoT
applications on a
self-powered
platform14.04.2021 21
Energy Harvesting Power Management Unit for a 500 nW SoC
- delivering different supply voltages
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• Wake-up receiver
(always-on), which
can receive data
packets at 8kb/s
• UWB transmitter with
On Off Keying
modulation
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Energy savings by up to several orders of magnitude from
using dedicated accelerators instead of the MCU
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Everactive (former Psikick) develops circuits depending
solely on energy harvesting, similar to Onio
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B. Calhoun, University of Virginia, one of the
founders of Everactive (former Psikick)
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Communication system
• Information: what is conveyed, in bits or
dits (decimal digits)
• In the transmitter, the information
modulates the carrier, i.e. is impressed on
a high-frequency sine wave.
• The signal will detoriate during
transmission through a channel, as a
result of some distortion or the introduction
of noise, which is unwanted energy.
• The receiver demodulates (and some
times decodes), which is the reverse of the
corresponding transmitter processes. The
destination could be a display,
loudspeaker or some computing device,
for example.14.04.2021 29
Amplitude Shift Keying – only the amplitude of the
carrier signal is modified in modulation
• Figure 1.2(a) shows a digital
message signal using two
voltage levels. One level
represents 1 and the other
represents 0. The unmodulated
carrier is illustrated in
Figure 1.2(b). Figure 1.2(c) and
(d) are the modulated waveforms
using two versions of ASK.
Figure 1.2(c) uses OOK, and
2(d) uses binary ASK, or BASK.• https://www.open.edu/openlearn/science-maths-
technology/exploring-communications-
technology/content-section-1.4
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14th of April
• Radio waves are electromagnetic waves travelling at the
speed of light, with a wavelength inversely proportional to
the frequency.
• The amplitude indicates the strength of the RF signal.
• Modulation changes the shape of a carrier wave to
somehow encode the speech or data information that we
were interested in carrying.
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Frequency shift keying – The frequency of the
carrier signal is modulated.
• In FSK, the frequency of
the carrier signal is
modified. An illustration of
binary FSK, or BFSK, is
given in Figure 1.4. Here,
bursts of a carrier wave at
one frequency or bursts of
a carrier wave at a second
frequency are transmitted
according to whether the
input data is 1 or 0.14.04.2021 32
Phase Shift Keying – simplest form; Binary PSK
• In BPSK, 0 and 1 are
represented by segments of
sinusoids that differ in their
phase. At the receiver,
distinguishing between the
two segments is easier if their
phases differ by as much as
possible. In BPSK the phases
are separated by half a cycle
(equivalent to π radians or
180°). See Figure.
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Quadrature Amplitude Modulation – combining ASK, FSK
and PSK to increase the number of symbols available
• Increasing the number of available symbols is a standard
way to increase the bit rate, because increasing the number
of symbols increases the number of bits per symbol. It is
rare for all three methods to be combined, but very common
for ASK and PSK to be combined to create Quadrature
amplitude modulation (QAM).
• QAM is based on the application of ASK and PSK to two
sinusoidal waves of the same frequency but with a phase
difference of 90°. Sinusoidal waves 90° apart are said to be
in a quadrature phase relationship. It is customary to refer
to one of these waves as the I wave, or in-phase wave or
component, and the other as the Q wave, or quadrature
wave or component (Figure in lower left corner).14.04.2021 34
Communication system
• Message from the
information source (words,
code, symbols etc)
• The information is in bits
or dits
• The signal is detoriated by
unwanted energy in the
channel – noise, having
it’s greatest effect when
the signal is weakest
• Ex: radio, fiber, optic14.04.2021 35
Block diagram of a typical amplitude-modulated broadcast
radio transmitter
• Ex.: converting sound signals to
electrical variations, restrict the
range of the audio frequencies and
compress their amplitude range
before modulation.
• A transmitter might have to
compress and possibly encode
information to make it suitable for
transmission.
• The information modulates the
carrier, i.e. is impressed on a sine
wave.
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Block diagram of AM superheterodyne receiver
• Ex.: F1=1GHz,
F2=0.75GHz, IF=250MHz
(filtered)
• Demodulation (and
sometimes also decoding)
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Literature, sources
Kennedy, George Electronic communication systems. 3rd- edition. McGraw-Hill
Publishing Co. Ltd., 1985.
Prof. Benton Calhoun - Self Powered System Design for Next Generation Wireless
Sensors , youtube / https://everactive.com/videos
https://www.open.edu/openlearn/science-maths-technology/exploring-
communications-technology/
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Next Wednesday – about the project
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