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.

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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

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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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