DIODES
Applications

EE314

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LED Light Emitting DiodesLD Laser DiodesFiber opticsOptical switching MEMSNanotechnologySolar CellsLight DetectionFuture Technologies

Diodes applications

Green electroluminescence from a point contact on a crystal of SiC recreates H. J. Round's original experiment from 1907.

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Light Spectrum

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Light Spectrum

Red, green and blue LEDs

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When a light-emitting diode is forward biased, electrons are able to recombine with holes within the device, releasing energy in the form of photons.

This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor.

LED - Light Emitting Diodes

Source http://en.wikipedia.org/wiki/Light-emitting_diode

LED - Light Emitting Diodes

UV AlGaN

Blue GaN, InGaN

Red, green GaP

Red, yellow GaAsP

IR- GaAs

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LED - Colors & voltage drop

ColorWavelength (nm)Voltage (V)Semiconductor MaterialInfrared > 760V < 1.9Gallium arsenide (GaAs) Aluminium gallium arsenide (AlGaAs)Red610 < < 7601.63 < V < 2.03Aluminium gallium arsenide (AlGaAs) Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)Orange590 < < 6102.03 < V < 2.10Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP)Gallium(III) phosphide (GaP)Yellow570 < < 5902.10 < V < 2.18Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)Green500 < < 5701.9 < V < 4.0Indium gallium nitride (InGaN) / Gallium(III) nitride (GaN) Gallium(III) phosphide (GaP)Aluminium gallium indium phosphide (AlGaInP) Aluminium gallium phosphide (AlGaP)Blue450 < < 5002.48 < V < 3.7Zinc selenide (ZnSe), Indium gallium nitride (InGaN), Silicon carbide (SiC) as substrate, Silicon (Si) Violet400 < < 4502.76 < V < 4.0Indium gallium nitride (InGaN)Purplemultiple types2.48 < V < 3.7Dual blue/red LEDs,blue with red phosphor,or white with purple plasticUltra-violet < 4003.1 < V < 4.4diamond (235nm), Boron nitride (215nm) , Aluminium nitride (AlN) (210nm) Aluminium gallium nitride (AlGaN) (AlGaInN) (to 210nm)WhiteBroad spectrumV = 3.5Blue/UV diode with yellow phosphor

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Wireless telemedicine

The PillCam is a swallow diagnostic device, taking high-quality, high-speed photos as it passes through the esophagus.

PillCam transmits 14 pictures/sec. to a receiver worn by the patient.

This enables diagnosis of throat disease and related ailments.

http://www.three-fives.com/latest_features/feature_articles/250205medical.html

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pn-junction laser

Light

Amplification by

Stimulated

Emission of

Radiation

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Diode Lasers are Small!

http://faculty.uml.edu/carmiento/Special%20Lectures/Intro%20to%20EE%20Lecture.pdf

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Radar/Laser Detectors

A radar/laser detector is a combination of a radar detector, which senses radar in the air, and a laser detector, which looks for laser beams directed at your car.

A laser beam is a very focused beam of light that does not separate out from its beam path.

Fortunately, there is a lot of dust and fine particles in the air, which causes the laser beam to separate enough that the beams can be seen by a proper detector.

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Optical Fiber Communications

What is it?

Transmission of information using light over an optical fiber

Why use it?

Extremely high data rate and wide bandwidth

Low attenuation (loss of signal strength)

Longer distance without repeaters

Immunity to electrical interference

Small size and weight

Longer life expectancy than copper or coaxial cable

Bandwidth can be increased by adding wavelengths

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Information Capacities in Optical Fiber

Each wavelength can carry a signal at 10 gigabits/sec (1010 bits/sec)

A fiber can transport up to 64 different wavelengths

Each wavelength can carry 10 Gb/s

Unlike electrical signals, optical signals inside the same fiber at different wavelengths dont interfere with each other

Each fiber can have an aggregate data rate of 640 Gb/s

This is 640,000,000,000 bits per second!

This rate translates to:

10 million simultaneous telephone calls (64 kb/s each)

Download the contents of the Library of Congress takes:

84 years using a 56 kb/s modem

0.22 seconds using the aggregate fiber rate

These rates can go much higher!

Researchers have developed operation of 40 Gb/s per wavelength

A fiber cable can contain as much as a hundred fibers

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Cable Size Comparison: Copper vs. Fiber

This is a standard copper cable used for telephone service. This carries about 300 phone calls

One of these fibers can carry up to 10 million telephone calls

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Optical Switching

Route optical communication signals without conversion to the electronic domain using microscopic mirrors based on MEMS technology

Where electrical and mechanical engineering meet

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MEMS: Miniature Motors

Human hair

Nanotechnology

Small and getting smaller

Video 2:30 min

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Micro and nanotechnologies are revolutionizing medicine

Almost invisible' tools are being developed by European researchers to discover diseases earlier and to treat patients better.

The miniaturization of instruments to micro and nano dimensions promises to make our future lives safer and cleaner.

In the "Adonis"-project, nano-sized gold particles are used to detect prostate cancer cells at an early stage.

http://www.zangani.com/node/2763

Video 7:30 min

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Photovoltaics

The word Photovoltaic is a combination of the Greek word for Light and the name of the physicist Allesandro Volta.

It identifies the direct conversion of sunlight into energy by means of solar cells. The conversion process is based on the photoelectric effect discovered by Alexander Bequerel in 1839.

The photoelectric effect describes the release of positive and negative charge carriers in a solid state when light strikes its surface.

http://www.solarserver.de/wissen/photovoltaik-e.html

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Photovoltaics

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Solar cells are composed of various semiconducting materials.

Semiconductors become electrically conductive when supplied with light or heat.

Over 95% of all the solar cells are composed of the Si.

How Does a Solar Cell Work?

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How Does a Solar Cell Work?

The usable voltage from solar cells depends on the semiconductor material. In silicon it amounts to approximately 0.5 V.

Terminal voltage is only weakly dependent on light radiation, while the current intensity increases with higher luminosity.

A 100 cm silicon cell, for example, reaches a maximum current intensity of approximately 2 A when radiated by 1000 W/m.

The equivalent circuit of a solar cell

Photo generated current

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Characteristics of a Solar Cell

The output power of a solar cell is temperature dependent. Higher cell temperatures lead to lower output, and hence to lower efficiency. Efficiency indicates how much of the radiated quantity of light is converted into useable electrical energy. Today on the order of 15-25%

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Light Detectors

Optical detectors,

Chemical detectors,

Photoresistors or Light Dependent Resistors (LDR)

Photovoltaic cells or solar cells

Photodiodes

Phototransistors

Optical detectors that are effectively thermometers, responding to the heat by the incoming radiation, such as pyroelectric detectors, Golay cells, thermocouples and thermistors,

Cryogenic detectors are sufficiently sensitive to measure the energy of single x-ray

Charge-coupled devices (CCD),

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CCD Detectors

An image is projected by a lens on the capacitor array causing each capacitor to accumulate an electric charge proportional to the light intensity at that location.

A charge-coupled device (CCD) is an analog shift register that transports electric charges through successive capacitors, controlled by a clock signal.

CCDs are used in digital photography, digital photogrammetry, astronomy, sensors, electron microscopy, medical fluoroscopy, optical and UV spectroscopy,etc.

CCD used for ultraviolet imaging in a wire bonded package.

CCD color sensor

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CCD Detectors

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Never connect an LED directly to a battery or a power supply!
It will be destroyed almost instantly because too much current will pass through and burn it out.

LEDs must have a resistor in series to limit the current to a safe value, for quick testing purposes a 1k resistor is suitable for most LEDs if your supply voltage is 12V or less.

Remember to connect the LED the correct way!

Testing an LED

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The most popular type of tri-color LED has a red and a green LED combined in one package with three leads.

They are called tri-color because mixed red and green light appears to be yellow.

The diagram shows the organization of a tri-color LED. Note the different lengths of the three leads.

The central lead (k) is the common cathode for both LEDs, the outer leads (a1 and a2) are the anodes to the LEDs allowing each one to be lit separately, or both together to give the third color.

Tri-color LEDs

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http://www.kpsec.freeuk.com/components/led.htm

An LED must have a resistor connected in series to limit the current through the LED. The resistor value, R is given by:

Calculating an LED resistor value

VS = supply voltage
VL = LED voltage (usually 2V, but 4V for blue and white LEDs)
I = LED current (e.g. 20mA), this must be less than the maximum permitted

If the calculated value is not available, choose the nearest standard resistor value which is greater, to limit the current. Even greater resistor value will increase the battery life but this will make the LED less bright.

For example

If the supply voltage VS = 9V, and you have a red LED (VL = 2V), requiring a current I = 20mA = 0.020A,
R = (9V - 2V) / 0.02A = 350, so choose 390 (the nearest greater standard value).

R = (VS - VL) / I

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An LED must have a resistor connected in series to limit the current through the LED, otherwise it will burn out almost instantly. The resistor value, R is given by:

R = (VS - VL) / I

If you wish to have several LEDs on at the same time, connect them in series.

This prolongs battery life by lighting several LEDs with the same current as just one LED.

The power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at least another 2V for the resistor.

To work out a value for the resistor you must add up all the LED voltages and use this for VL.

Connecting LEDs in series

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Connecting LEDs in series

Example

A red, a yellow and a green LED in series need a supply voltage of at least 32V+2V=8V,

so choose a 9V battery. Adjust the resistor R to have current I=15 mA.

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Connecting LEDs in series

Example

A red, a yellow and a green LED in series need a supply voltage of at least 32V+2V=8V,

so choose a 9V battery. Adjust the resistor R to have current I=15 mA.

VL = 2V + 2V + 2V = 6V (the three LED voltages added up).

If the supply voltage VS is 9V and the current I must be 15mA = 0.015A,

Resistor R = (VS - VL) / I = (9 - 6) / 0.015 = 3 / 0.015 = 200,
so choose R = 220 (the nearest standard value which is greater).

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Connecting several LEDs in parallel with just one resistor shared between them is a bad idea.

If the LEDs require slightly different voltages only the lowest voltage LED will light and it may be destroyed by the larger current flowing through it.

If LEDs are in parallel each one should have its own resistor.

Avoid connecting LEDs in parallel!

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LED displays are packages of many LEDs arranged in a pattern, the most familiar pattern being the 7-segment displays for showing numbers (digits 0-9).

LED Displays

It is a common anode display since all anodes are joined together and go to the positive supply.

The cathodes are connected individually to resistors limiting the current through each diode to a safe value.

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Using Varicap Diode

When the junction diode is reverse biased, the insulating barrier widens reducing diode capacitance.

The barrier forms the dielectric, of variable width, of a capacitor.

The N and P type cathode and anode are the two plates of the capacitor.

In the diagram, the diode and coil form a resonant circuit.

The capacitance of the diode, and thereby the resonant frequency, is varied by means of the potentiometer controlling the reverse voltage across the varicap.

The capacitor prevents the coil shorting out the voltage across the potentiometer.

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Ideality factor (m) depends on junction gradient

Diode Capacitance as a Funcion of VD

Nanotechnology 101

Nanotechnology is the art and science of manipulating matter at the nanoscale (down to 1/100,000 the width of a human hair) to create new and unique materials and products.

Nanotechnology has enormous potential to change society.

An estimated global research and development investment of nearly $9 billion per year is anticipated to lead to:

new medical treatments and tools; more efficient energy production, storage and transmission; better access to clean water; more effective pollution reduction and prevention; and stronger, lighter materials and many other uses.

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Nanotechnology 101

So what?

The nanoscale is the scale of atoms and molecules.

At the nanoscale, scientists can start affecting the properties of materials directly, making them harder or lighter or more durable.

In some cases, simply making things smaller changes their properties:

a chemical might take on a new color, or start to conduct electricity. nanoscale particles are more chemically reactive with more surface areananotubes made of carbon, can be up to thirty times stronger than steel, yet is one sixth the weight.

http://www.nanotechproject.org/topics/nano101/introduction_to_nanotechnology/

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Nanotechnology 101

Carbon nanotubes make bicycle frames and tennis rackets lighter and stronger. Nano-sized particles of titanium dioxide and zinc oxide are used in sunscreens. Nanoscale silver is antimicrobial and prevents food stored in plastic bags from going bad. Clothes treated with nano-engineered coatings are stain-proof or static-free. Computer chips using nanoscale components are used anywhere from computers to mp3 players, digital cameras to video game consoles

Dollars and Sense

In 2007, $60 billion worth of nano-enabled products were sold.

Nanotechnology will produce an anticipated 7 million jobs in the next decade.

By 2014, $2.6 trillion in manufactured goods will incorporate nanotechnology.

nanotubes

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Future Technologies

Future technology videos

Part1: 7:00 min

Part2: 7:50 min

Part3: 7:22 min

Part4: 8:24 min

Part5: 7:30 min

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