EC6202 ELECTRONIC DEVICES AND CIRCUITS

Unit 1

Dr Gnanasekaran Thangavel

Professor and Head

Electronics and Instrumentation

Engineering

R M K Engineering College

Electronic components

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Classification

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Active components

Rely on a source of energy and can inject power into a circuit

Passive components

Can't introduce net energy into the circuit and can't rely on a

source of power

Electromechanical

can carry out electrical operations by using moving parts or by

using electrical connections

Active components

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Semiconductors

Diodes

Transistors

Integrated circuits

Optoelectronic devices

Display technologies

Vacuum tubes (valves)

Discharge devices

Power sources

Passive components

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Resistors

Capacitors

Magnetic (inductive) devices

Memristor

Networks

Transducers, sensors, detectors

Antennas

Assemblies, modules

Electromechanical

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Passive components that use piezoelectric effect:

Components that use the effect to generate or filter high frequencies

Crystal – a ceramic crystal used to generate precise frequencies (See the Modules class below for complete oscillators)

Ceramic resonator – Is a ceramic crystal used to generate semi-precise frequencies

Ceramic filter – Is a ceramic crystal used to filter a band of frequencies such as in radio receivers

Surface acoustic wave (SAW) filters

Components that use the effect as mechanical transducers.

Ultrasonic motor – Electric motor that uses the piezoelectric effects

For piezo buzzers and microphones,

UNIT I PN JUNCTION DEVICES

PN junction diode –structure, operation and V-I

characteristics, diffusion and transient capacitance -

Rectifiers – Half Wave and Full Wave Rectifier,– Display

devices- LED, Laser diodes- Zener diode characteristics-

Zener Reverse characteristics – Zener as regulator

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1. https://www.youtube.com/watch?v=OyC02DWq3mI

2. https://www.youtube.com/watch?v=d4zO39K_ce8

3. https://www.youtube.com/watch?v=AspBbh_jOuk

4. https://www.youtube.com/watch?v=UMgOG4OqBT0

5. https://www.youtube.com/watch?v=Kl8IOESVWlM

PN junction diode

Definition

“A semiconductor device with two terminals, typicallyallowing the flow of current in one direction only.

“A diode is a specialized electronic component with twoelectrodes called the anode and the cathode. They aremade with semiconductor materials such as silicon,germanium, or selenium. The fundamental property of adiode is its tendency to conduct electric current in onlyone direction.”

“A Diode is an electronic device that allows current to flowin one direction only. It is a semiconductor that consists ofa p-n junction. They are used most commonly to convertAC to DC”.

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Semiconductors and Physical Operation of

Diodes

Semiconductors

Doping

• n-type material

• p-type material

pn-Junctions

• forward, reverse, breakdown

• solar cells, LEDs, capacitance

Periodic Table of Elements

Relevant Columns: III IV V

The Silicon Atom

Nucleus:14 protons14 neutrons

10 core electrons:1s22s22p6

-

-

-

-

4 valenceelectrons

The 4 valence electrons are responsible for forming covalent bonds

Silicon CrystalEach Si atom has four nearest neighbors — one for each valence electron

0.5 nm

Two-dimensional Picture of Sinote: each line ( —) represents a valence electron

covalent bond

At T=0 Kelvin, all ofthe valence electrons are participating in covalent bonds

There are no “free”electrons, therefore no current can flow in the silicon INSULATOR

Si

Silicon at Room Temperature

For T>0 K, the silicon atomsvibrate in the lattice. This iswhat we humans sense as “heat.”

Occasionally, the vibrationscause a covalent bond to breakand a valence electron is freeto move about the silicon.

Silicon at Room Temperature

-

-

For T>0 K, the silicon atomsvibrate in the lattice. This iswhat we humans sense as “heat.”

Occasionally, the vibrationscause a covalent bond to breakand a valence electron is freeto move about the silicon.

= free electron

Silicon at Room Temperature

The broken covalent bond siteis now missing an electron.

This is called a “hole”

The hole is a missing negativecharge and has a charge of +1.

= a hole

-

+

hole

Current Flow in Silicon

*

+ -

+-

a bar of silicon

I

V

Bond breakingdue to:-heat (phonons)-light (photons)

Conductance isproportional tothe number ofelectrons and holes:Si resistancedepends on temp. and light

Some important facts

The number of electrons = the number of holes that is, n = p in pure silicon

this is called intrinsic material

High temp more electrons/holes lower resistance

Very few electrons/holes at room temperature n=1.5x1010 per cm3, but nSi = 5x1022 per cm3

n/nSi = 3x10-13 (less than 1 in a trillion Si bonds are broken

This is a SEMICONDUCTOR

Important Facts (cont.)

Band Gap: energy required to break a covalent bond and free an electron Eg = 0.66 eV (germanium)

Eg = 1.12 eV (silicon)

Eg = 3.36 eV (gallium nitride)

Metals have Eg= 0 very large number of free electrons high conductance

Insulators have Eg > 5 eV almost NO free electrons zero conductance

Doping

Intentionally adding impurities to a semiconductor to create more free electrons OR more holes (extrinsic material)

n-type material more electrons than holes (n>p)

p-type material more holes than electrons (p>n)

HOW???

Periodic Table of ElementsRelevant Columns: III IV V

n-type siliconadd atoms from column V of the periodic table

Si

P

-

Column V elements have 5 valence electrons

Four of the electrons form covalent bonds with Si, but the 5th electron is unpaired.

Because the 5th electron is weakly bound, it almost always breaks away from the P atom

This is now a free electron.

VERY IMPORTANT POINT

Si

P+

-

The phosphorus atom has donated an electron to the semiconductor (Column V atoms are called donors)

The phosphorus is missing one of its electrons, so it has a positive charge (+1)

The phosphorus ion is bound to the silicon, so this +1 charge can’t move!

The number of electrons is equal tothe number of phos. atoms: n = Nd

Periodic Table of ElementsRelevant Columns: III IV V

p-type siliconadd atoms from column III of the periodic table

Si

B

Column III elements have 3 valence electrons that form covalent bonds with Si, but the 4th

electron is needed.

This 4th electron is taken from the nearby Si=Si bond

p-type siliconadd atoms from column III of the periodic table

Si

B

Column III elements have 3 valence electrons that form covalent bonds with Si, but the 4th

electron is needed.

This 4th electron is taken from the nearby Si=Si bond

This “stolen” electron creates a free hole.

hole

VERY IMPORTANT POINT

Si

B-

+

The boron atom has accepted an electron from the semiconductor (Column III atoms are called acceptors)

The boron has one extra electron, so it has a negative charge (-1)

The boron ion is bound to the silicon, so this -1 charge can’t move!

The number of holes is equal tothe number of boron atoms: p = Na

The pn Junction

p-type n-type

anode cathode

integrated circuit diode

metalsilicon oxide

doped siliconwafer (chip)

Dopant distribution inside a

pn junction

p>>n n>>p

excess electrons diffuseto the p-type region

excess holes diffuseto the n-type region

n~0, and donor ions are exposed

Dopant distribution inside a

pn junction

excess electrons diffuseto the p-type region

excess holes diffuseto the n-type region

DEPLETION REGION:

+

p~0, and acceptor ions are exposed

p>>n n>>p

+

+

+-

-

-

-

Voltage in a pn junction

p>>n n>>p

+

+

+-

-

-

-x

charge, r(x)

x

x

electric field,E(x)

voltage,V(x)

+

~0.7 volts(for Si)

x

dxxxE0

)(1

)( r

x

dxxExV0

)()(

Zero Bias

p>>n n>>p

+

+

+-

-

-

x

voltage,V(x)

~0.7 volts(for Si)

At zero bias (vD=0), very few electrons or holes can overcome this built-in voltage barrier of ~ 0.7 volts (and exactly balanced by diffusion)

iD = 0

Forward Bias

p>>n n>>p

+

+

+-

-

-

x

voltage,V(x)

0.65 volts

As the bias (vD), increases toward 0.7V, more electrons and holes can overcome the built-in voltage barrier . iD > 0

vD

0.50 volts

0.0 volts

Reverse Bias

p>>n n>>p

+

+

+-

-

-

x

voltage,V(x)

-5 volts

As the bias (vD) becomes negative, the barrier becomes larger. Only electrons and holes due to broken bonds contribute to the diode current. iD = -Is

vD

0.0 volts

1/2Is

1/2Is

Is

Breakdown

p>>n n>>p

+

+

+-

-

-

x

voltage,V(x)

-50 volts

As the bias (vD) becomes very negative, the barrier becomes larger. Free electrons and holes due to broken bonds are accelerated to high energy (>Eg) and break other covalent bonds – generating more electrons and holes (avalanche).

vD

0.0 volts

|I| >> Is

large reverse current

Solar Cell (Photovoltaic)

p>>n n>>p

+

+

+-

-

-

x

voltage,V(x)

~0.7 volts(for Si)

Light hitting the depletion region causes a covalent bond to break. The free electron and hole are pushed out of the depletion region by the built-in potential (0.7v).

Rload

light

Iph

Light Emitting Diode (LED)

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A light-emitting diode (LED) is a two-lead semiconductor light

source. It is a p–n junction diode that emits light when activated.

When a suitable voltage is applied to the leads, electrons are able to

recombine with electron holes within the device, releasing energy in

the form of photons. This effect is called electroluminescence, and

the colour of the light (corresponding to the energy of the photon) is

determined by the energy band gap of the semiconductor.

Light Emitting Diode (LED)

p>>n n>>p

+

+

+-

-

-

x

voltage,V(x)

2.0 volts

In forward bias, an electron and hole collide and self-annihilate in the depletion region. A photon with the gap energy is emitted. Only occurs in some materials (not silicon).

vD

1.5 volts

0.0 volts

photon

Junction Capacitance

p>>n n>>p

+

+

+-

-

-

Wn=p~0

=11.9

semiconductor-”insulator”-semiconductor

The parasitic (unwanted) junction capacitance is

Cj = eA/W, where W depends on the bias voltage

A

Junction Capacitance (Cj)

The junction capacitance must be charged and discharged every time the diode is turned on and off

Transistors are made of pn junctions. The capacitance due to these junctions limits the high frequency performance of transistors remember, Zc = 1/jwC becomes a short circuit at high frequencies (Zc 0) this means that a pn junction looks like a short at high frequency

This is a fundamental principle that limits the performance of all electronic devices

HALF WAVE RECTIFIER

The Half wave rectifier is a circuit, whichconverts an ac voltage to dc voltage.The primary of the transformer isconnected to ac supply. This induces anac voltage across the secondary of thetransformer.

During the positive half cycle of the inputvoltage the polarity of the voltage acrossthe secondary forward biases the diode.As a result a current IL flows through theload resistor, RL. The forward biaseddiode offers a very low resistance andhence the voltage drop across it is verysmall. Thus the voltage appearing acrossthe load is practically the same as theinput voltage at every instant.

HALF WAVE RECTIFIER …….

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During the negative half cycle of the input voltage the polarity of

the secondary voltage gets reversed. As a result, the diode is

reverse biased.

Practically no current flows through the circuit and almost no

voltage is developed across the resistor. All input voltage

appears across the diode itself.

Hence we conclude that when the input voltage is going through

its positive half cycle, output voltage is almost the same as the

input voltage and during the negative half cycle no voltage is

available across the load. This explains the unidirectional

pulsating dc waveform obtained as output. The process of

removing one half the input signal to establish a dc level is aptly

called half wave rectification.

The output waveform

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FULL WAVE RECTIFIER

• A Full Wave Rectifier is a circuit, which converts an ac voltage into

a pulsating dc voltage using both half cycles of the applied ac

voltage. It uses two diodes of which one conducts during one half

cycle while the other conducts during the other half cycle of the

applied ac voltage.

The output waveform

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Positive cycle, D2 off, D1 conducts;

Vo – Vs + V = 0

Vo = Vs - V

Full-Wave Rectification – circuit with center-

tapped transformer

Since a rectified output voltage occurs during both positive and

negative cycles of the input signal, this circuit is called a full-

wave rectifier.

Also notice that the polarity of the output voltage for both

cycles is the same

Negative cycle, D1 off, D2 conducts;

Vo – Vs + V = 0

Vo = Vs - V

Vs = Vpsin t

V

-V

Notice again that the peak voltage of Vo is lower since Vo = Vs -

V

Vp

• Vs < V, diode off, open circuit, no current flow,Vo = 0V

Positive cycle, D1 and D2 conducts, D3 and D4 off;

+ V + Vo + V – Vs = 0

Vo = Vs - 2V

Full-Wave Rectification –Bridge Rectifier

Negative cycle, D3 and D4 conducts, D1 and D2 off

+ V + Vo + V – Vs = 0

Vo = Vs - 2V

Also notice that the polarity of the output voltage for both cycles is the same

A full-wave center-tapped rectifier circuit is shown in Fig. 3.1. Assume that for each diode,

the cut-in voltage, V = 0.6V and the diode forward resistance, rf is 15. The load

resistor, R = 95 . Determine:

peak output voltage, Vo across the load, R

Sketch the output voltage, Vo and label its peak value.

25: 1

125 V (peak voltage)

( sine wave )

SOLUTION

peak output voltage, Vo

Vs (peak) = 125 / 25 = 5V

V +ID(15) + ID (95) - Vs(peak) = 0 ID = (5 – 0.6) / 110

= 0.04 A Vo (peak) = 95 x 0.04 = 3.8V

3.8V

Vo

t

Duty Cycle: The fraction of the wave cycle over which the

diode is conducting.

EXAMPLE 3.1 – Half Wave Rectifier

Determine the currents and voltages of the half-wave rectifier circuit. Consider the half-wave rectifier circuit

shown in Figure.

Assume and . Also assume that

Determine the peak diode current, maximum reverse-bias diode voltage, the fraction of the wave cycle over

which the diode is conducting.

A simple half-wave battery charger circuit

-VR + VB + 18.6 = 0

VR = 24.6 V

- VR +

+

-

The peak inverse voltage (PIV) of the diode is the

peak value of the voltage that a diode can withstand

when it is reversed biased

Type of

Rectifier

PIV

Half Wave Peak value of the input secondary voltage, Vs (peak)

Full Wave :

Center-Tapped

2Vs(peak) - V

Full Wave: Bridge Vs(peak)- V

Example: Half Wave Rectifier

Given a half wave rectifier with input primary voltage, Vp = 80 sin t and the

transformer turns ratio, N1/N2 = 6. If the diode is ideal diode, (V = 0V), determine the

value of the peak inverse voltage.

1. Get the input of the secondary voltage:

80 / 6 = 13.33 V

1. PIV for half-wave = Peak value of the input voltage = 13.33 V

EXAMPLE 3.2

Calculate the transformer turns ratio and the PIV voltages for each type of the full wave rectifier

a) center-tapped

b) bridge

Assume the input voltage of the transformer is 220 V (rms), 50 Hz from ac main line source. The desired peak

output voltage is 9 volt; also assume diodes cut-in voltage = 0.6 V.

Solution: For the centre-tapped transformer circuit the peak voltage of the transformer secondary

is required

The peak output voltage = 9V

Output voltage, Vo = Vs - V

Hence, Vs = 9 + 0.6 = 9.6V

Peak value = Vrms x 2

So, Vs (rms) = 9.6 / 2 = 6.79 V

The turns ratio of the primary to each secondary winding is

The PIV of each diode: 2Vs(peak) - V = 2(9.6) - 0.6 = 19.6 - 0.6 = 18.6 V

Solution: For the bridge transformer circuit the peak voltage of the transformer secondary is

required

The peak output voltage = 9V

Output voltage, Vo = Vs - 2V

Hence, Vs = 9 + 1.2 = 10.2 V

Peak value = Vrms x 2

So, Vs (rms) = 10.2 / 2 = 7.21 V

The turns ratio of the primary to each secondary winding is

The PIV of each diode: Vs(peak)- V = 10.2 - 0.6 = 9.6 V

Laser diodes

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LASER — Light Amplification by Stimulated Emission of Radiation

The Laser is a source of highly directional, monochromatic, coherent light.

The Laser operates under a “stimulated emission” process.

The semiconductor laser differs from other lasers (solid, gas, and liquid lasers):

small size (typical on the order of 0.1 × 0.1 × 0.3 mm3)

high efficiency

the laser output is easily modulated at high frequency by controlling the junction current

low or medium power (as compared with ruby or CO2 laser, but is comparable to the He-Ne

laser)

particularly suitable for fiber optic communication

Important applications of the semiconductor lasers:

optical-fiber communication, video recording, optical reading, high-speed laser printing.

high-resolution gas spectroscopy, atmospheric pollution monitoring.

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Comparison between an LD and LED

Laser Diode

Stimulated radiation

narrow line width

coherent

higher output power

a threshold device

strong temperature dependence

higher coupling efficiency to a fiber

LED

Spontaneous radiation

broad spectral

incoherent

lower output power

no threshold current

weak temperature dependence

lower coupling efficiency

Laser Diode Construction

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The figure shows a simplified construction of a laser diode, which is similar to a light emitting diode (LED).

It uses gallium arsenide doped with elements such as selenium, aluminum, or silicon to produce P type and N type semiconductor materials.

While a laser diode has an additional active layer of undoped (intrinsic) gallium arsenide have the thickness only a few nanometers, sandwiched between the P and N layers, effectively creating a PIN diode (P type-Intrinsic-N type). It is in this layer that the laser light is produced.

How Laser Diode Work?

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Every atom according to the quantumtheory, can energies only within a certaindiscrete energy level. Normally, the atomsare in the lowest energy state or groundstate.

When an energy source given to the atomsin the ground state can be excited to go toone of the higher levels. This process iscalled absorption.

After staying at that level for a very shortduration, the atom returns to its initialground state, emitting a photon in theprocess, This process is calledspontaneous emission.

These two processes, absorption andspontaneous emission, take place in a

How Laser Diode Work?

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In case the atom, still in an excited state, is struck by an outside photon having

precisely the energy necessary for spontaneous emission, the outside photon is

increased by the one given up by the excited atom, Moreover, both the photons

are released from the same excited state in the same phase, This process, called

stimulated emission, is fundamental for laser action (shown in above figure).

In this process, the key is the photon having exactly the same wavelength as that

of the light to be emitted.

Amplification and Population Inversion

When favorable conditions are created for the stimulated emission, more and more

atoms are forced to emit photons thereby initiating a chain reaction and releasing

an enormous amount of energy.

This results in a rapid build up of energy of emitting one particular wavelength

(monochromatic light), travelling coherently in a particular, fixed direction. This

process is called amplification by stimulated emission.

Laser Diode Laser diode is an improved LED, in the sense that uses stimulated emission in semiconductor from

optical transitions between distribution energy states of the valence and conduction bands with

optical resonator structure such as Fabry-Perot resonator with both optical and carrier

confinements.

Laser Diode Characteristics

Nanosecond & even picoseconds response time (GHz BW)

Spectral width of the order of nm or less

High output power (tens of mW)

Narrow beam (good coupling to single mode fibers)

Laser diodes have three distinct radiation modes namely,

longitudinal, lateral and transverse modes.

In laser diodes, end mirrors provide strong optical feedback in

longitudinal direction, so by roughening the edges and cleaving

the facets, the radiation can be achieved in longitudinal

direction rather than lateral direction.

Zener Diode

A Zener diode is a type of diode that permits current not only in

the forward direction like a normal diode, but also in the reverse

direction if the voltage is larger than the breakdown voltage

known as "Zener knee voltage" or "Zener voltage".

Zener Diode - Voltage Regulator (reverse

biased)

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References1. David A. Bell ,”Electronic Devices and Circuits”, Prentice Hall of India,.

2. staff.iium.edu.my/.../L6%20and%20L7%20full%20wave%20rectifier,%20PIV.ppt

3. www.ece.neu.edu/.../eceg201/.../Semiconductors_and_Physical_Operation_of_Diodes...

4. http://www.electronics-tutorials.ws/diode/diode_3.html.

5. http://www.electronicsandyou.com/electronics-basics/diode.html

6. https://en.wikipedia.org/wiki/Light-emitting_diode

7. http://www.circuitstoday.com/half-wave-rectifiers

8. http://www.visionics.a.se/html/curriculum/Experiments/HW%20Rectifier/Half%20Wave%20Rectifi

er1.html

9. eshare.stust.edu.tw/EshareFile/2010_5/2010_5_4fc2dc4c.ppt

10. https://ece.uwaterloo.ca/~ece477/Lectures/ece477_4_0.ppt

11. https://www.elprocus.com/laser-diode-construction-working-applications/

12. www.ohio.edu/people/starzykj/network/Class/.../Lecture5%20Diode%20Circuits.ppt

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Other presentations

http://www.slideshare.net/drgst/presentations

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Thank You

Questions and Comments?

Dr Gnanasekaran Thangavel 7/19/2017