LED Lighting Visible Light Communication (VLC)conferences.dbuniversity.ac.in/egtet2020/wp... · VLC = Visible Light Communication (downlink only) Slide 17 Types of OWC and Their Applications

LED Lighting&

Visible Light Communication (VLC)

Dr. Karel L Sterckx

[email protected]

http://bucroccs.bu.ac.th

EGTET 2020

6-7 March 2020

Outline

Semiconductor and Diode Basics

LED Lighting

High Brightness LEDs

LED Drivers

The LED Lighting Advantage

Eye Safety Issues

VLC Concept

Types of Optical Wireless Communication (OWC) and Their Applications

VLC Antennas

Merits of VLC

Drawbacks of VLC & Measures to mitigate these

OWC Standards

Slide 2

Semiconductor Basics

Material with an electrical conductivity between that of a metal and an insulator

Consists of either

Single elements that have 4 electrons on the outer shell

Compound of elements that have 3 and 5 electrons on the outer shell

Conductivity may be altered by introducing impurities (doping)

Donor impurities create N material

• Has free electrons at room temperature

Acceptor impurities create P material

• Leaves holes in the crystalline structure

• Since holes are able to attract electrons, they are considered positive

Figures on the next slide show

Silicon (Si) atom

Creation of P and N material

Slide 3

Semiconductor Basics (2)

Slide 4

E

Intrinsic (I) material P material N material

≡≡≡≡

Si14

Ge32

Al13

Ga31

In49

P15

As33

Sb51

III IV VAl = Aluminium

Ga = GalliumIn = Indium

Si = Silicon

Ge = Germanium

P= PhosphorusAs = Arsenic

Sb = Antimony

Intrinsic Si: ~5x1022 atoms/cm3

Doping Concentrations: 1013-1018 atoms/cm3

Diode Basics

Diode, Light Emitting Diode (LED) and Photodiode are essentially the same

Semiconductor device that consists of P and N-material

In reality, N and P regions are grown on a substrate

Electrons migrate to fill holes → electrons and holes combine

P and N material become negatively and positively charged, respectively

Migration stops after the voltage created by the migrated charge carriers reaches a certain value

Between P and N, a depletion zone (depleted of free charge carriers) is created

Slide 5

-- - -- --

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-- -- --

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depletion zone (intrinsic)

- +

I

Diode Basics

When electron and hole combine, a energy packet is released in the form of a photon (= elementary particle of light)

Diode in forward bias

Current-to-light conversion

LED

Diode in reverse bias

Light-to-current conversion

Photodiode

Slide 6

-- -- --

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light

+ -current

-- -- --

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P I N- +

Photodiode vs solar cell

In principle, they are the same

Photo Diode

Response time (speed) is important → Depletion zone is kept minimal to reduce junction capacitance

To further reduce the junction capacitance (to increase the response time), a photodiode may be negative biased (= photocurrent mode)

Solar cell

Response time is of no importance

The amount of captured sunlight is important → Depletion zone is very large

As it makes no sense to apply a voltage over a solar cell, it is never negative biased (= photovoltaic mode)

Slide 7

LED

Slide 8

Wavelength (colour) depends on the semiconductor compound

Forward voltage drop over depletion zone increases with emitted frequency

http://lednique.com/tag/led

High Brightness LEDs (HBLEDs)

Divide between LED and HBLED is somewhat arbitrary →→→→Efficacy > 50 lumens/watt is often quoted

Efficiency

Blue and UV: About 80%

Red: About 60%

Green: About 30%

White HBLEDs, in fact, emit blue light

Part of the light converted by a yellow phosphor

Converted part and non-converted part mixed to obtain white light of desired colour temperature (warm or pure white)

Material: InAlGaN

Slide 9

https://ledheadgrowlights.com/blogs

/news/red-white-or-blue-choosing-

the-right-led-color

High Brightness LEDs (2)

Coloured HBLEDs

InAlGaN emitting UV light

All light converted by a phosphor to obtain the desired colour

RGB HBLED

R = InAlGaP

G and B = InAlGaN

Due to limited efficiency of R and G used in displays only

Slide 10

LED Drivers

Constant current source

LEDs convert current to light!

Up to saturation, this conversion is linear

Requirements

Power Effective

Isolate LEDs from the mains (220V/50Hz in India)

Driver that fulfils both requirements

Flyback

Drivers that fulfil only the first requirement (used when powered by low DC voltage, e.g. certain spotlights)

Buck (Supply voltage higher than total forward voltage over LEDs)

Boost (Supply voltage lower than total forward voltage over LEDs)

Buck/Boost (Both lower and higher supply voltages)

SEPIC (Both lower and higher supply voltages)

Slide 11

The LED Lighting Advantage

More power efficient: 80% vs 50% compared to Compact Fluorescent Lamps (CFLs)

Larger life times: 5-10 times longer (25-50 years)

No degrading in performance over time

No hazardous materials such as mercury and halides

No burning hazard as LED lamps become lukewarm only

Only drawback used to be acquisition price →→→→ Issue has been addressed and prices have become competitive with those of gas discharge lamps

Slide 12

Eye Safety Issues

Slide 13

https://en.m.wikipedia.org/wiki/Eye

Eye Safety Issues (2)

With regard to visible light, the retina is a risk

Retina is the human photodetector

Consists of cones that detect Red, Green and Blue (RGB) light, respectively

Retina is most sensitive to shorter wavelengths, i.e. blue light

For LED lighting, the blue component is the primary concern

Iris absorbs visible light →→→→ Closes more at higher intensities

Lens absorbs blue light

Lenses of young people pass about 65% of blue light

Around 25 years, only 20% of blue light is passed → adult eye filters blue light a lot more

In aging eyes, scattering may increase →→→→ blurred vision

Particular problem for blue light

Older people may not see blue LED displays clearly

Slide 14

Eye Safety Issues (3)

According to a recent (2017) 92 page study commissioned by the European Union, there is no evidence of direct adverse health effects from LED emission in normal use (lamps and displays)

However, it is advisable to closely monitor long terms effects as this data is not yet available

In environments populated by children, it is advisable to use warm white light instead of cold white light

Slide 15

https://ec.europa.eu/health/sites/health/files/scientific_committees/scheer/docs/scheer_o_011.pdf

Visible Light Communication (VLC)

LED lights can be switched rapidly

Human eye detects average intensity

Photodetector sees zeros and ones

LED lighting can also wirelessly transmit data

Concept is known as VLC

Slide 16

http://visiblelightcomm.com/wp-

content/uploads/2013/03/VLC.png

Types of OWC and Their Applications

OWC = Optical Wireless Communication

Wireless Connectivity via a light carrier

Carrier = Infrared (Ir), visible light of any colour, or Ultra Violet (UV)

VLC = Visible Light Communication (downlink only)

Slide 17

Types of OWC and Their Applications (2)




VLC = Visible Light Communication (up- and downlink)

Slide 18

www.naka-lab.jp/product/uvlc_feature_e.html





VLC = Visible Light Communication

IrWC = Infrared Wireless Communication

Slide 19

VLC

IrWC







FSO = Free Space Optics

Slide 20

Wireless ‘Last Mile’

Fixed Line







FSO = Free Space Optics

UVWC = Ultraviolet Wireless Communication

Slide 21

http://spectrum.ieee.org/aerospace/military/ultraviolet-radios-beam-to-life

VLC Antennas

Slide 22

Transmitter (TX)

Light Emitting Diode (LED)

Until saturation

Almost every recombination of an electron–hole pair excites a photon

Current-to-intensity conversion is linear

Wavelength (colour) depends on semiconductor compound

Bandwidth limiting factor: Junction Capacitance

Receiver (RX)

Large Area Photodiode (Si-PIN)

Until saturation

Almost every photon that is absorbed excites an electron hole-pair

Intensity-to-current conversion is linear

Converts near Ir (sensitivity peak around 850 nm) and visible light

Bandwidth limiting factor: Junction Capacitance

Modulation Format: Intensity Modulation (IM)/Direct Detection (DD)BEWARE: Unipolar

Infrared Emitting Diode (IrED)

Used in Infrared Wireless Communication (IrWC), including uplink in LiFi Systems

Emission level restricted by eye safety standards

Material: GaAs or AlGaAs

Threshold voltage about 1.6 V

Slide 23

Only practical photo detector for VLC and IrWC to date

Intrinsic layer between P and N layer to enlarge the photosensitive junction →→→→ Also increases the junction capacitance

Receives both visible light and near Ir

Si PIN Photodiode

www.repairfaq.org/sam/sipdresp.gif

Merits of VLC

Larger bandwidth (factor 1,000) and entirely license free

BEWARE: License free ≠≠≠≠ Unregulated

Does not cause and is not affected by EMI

Cheaper transceiver components and less complex transceiver designs

Light cannot penetrate walls and other opaque objects →→→→Security at the physical layer

Footprint can be more accurately designed

No fading as the photosensitive detection area is much larger than the wavelength of the carrier

Slide 25

Drawbacks of VLC & Measures To Mitigate

Capacitances of LED and photodiode limit attainable bandwidth

Equalisation at TX (active) or RX (passive)

Multicarrier transmission

At RX, TIA isolates, to a certain extend, the capacitance of photodiode

Transmission power restricted by eye safety regulations,

Sensitive RX required (especially for Ir light)

Background Noise caused by ambient light

Mitigated via HPF

Multipath dispersion (MPD) as the signal reaches the receiver through various paths of different length

Multicarrier Transmission

High dynamic range

Automatic Gain Control (AGC)

Drive voltage amplifier of RX into saturation (digital signals only)

Slide 26

OWC Standards

IEEE 802.15.7-2018

IEEE Standard for Local and metropolitan area networks - Part 15.7: Short-Range Optical Wireless Communications

Defines a physical layer (PHY) and medium access control (MAC) sublayer for short-range OWC

https://ieeexplore.ieee.org/document/8697198

IEEE 802.15 WPAN Task Group 13 (TG13) Multi-Gigabit/s Optical Wireless Communications

www.ieee802.org/15/pub/TG13.html

Standard (IEEE 802.15.13) targeted for publication in Q4 2020

Slide 27

Thank you for your attention!Questions?

Dr. Karel L SterckxDirector BU-CROCCS

[email protected]

http://bucroccs.bu.ac.th

Documents

LED Lighting Visible Light Communication (VLC)conferences.dbuniversity.ac.in/egtet2020/wp... · VLC = Visible Light Communication (downlink only) Slide 17 Types of OWC and Their Applications