Electronics Engineering 1

Prepared by: Armando V. Barretto

Final Grade = (Q1+Q2+Q3+Q4+2FE+2PE)/8

Passing Grade=>60

References• Electronic Devices and Circuit Theory by Boylestad and Nashelsky• Principles of Electronic Devices by William D. Stanley• Electronic Principles and Applications by A. B. Bhattacharya• Electronic Circuit Analysis and Design by Donald A. Neamen• Electronics Made Simple by Henry Jacobowitz• Teach Yourself Electricity and Electronics by Stan Gibilisco• Electron Devices by Bakshi and Godse• Electronic devices and circuits: principles and applications by Deshpande• Integrated Electronics by Millman and Halkias

Grading System

Course Outline• Atomic Structure and Electron Emission • Vacuum tubes• Semiconductor Materials• Semiconductor Diode• Semiconductor Diode Circuit Analysis• Rectifiers Using Semiconductor Diodes• Clippers• Resistor- Capacitor (RC) Networks• Clampers• Voltage Multiplier Circuits• Zener Diode Applications• Bipolar Junction Transistors (BJT)• Bipolar Junction Transistor (BJT) DC Biasing• Bipolar Junction Transistor (BJT) Bias Stabilization• Bipolar Junction Transistor (BJT) Amplifier Basic Design• Bipolar Junction Transistor (BJT) Small AC signal Analysis

– Bipolar Junction Transistor (BJT) Hybrid Equivalent Model

Course Outline

– Bipolar Junction Transistor (BJT) Hybrid Model– Bipolar Junction Transistor (BJT) Z Parameter and Y Parameter Models

Atomic Structure And Electron Emission

Prepared by: Armando V. Barretto

Brief History• 1802 – John Dalton performed experiments that showed that matters consist of

elementary particles, and he suggested that all matters could be broken down into elements which is composed of particles he called atoms (Greek word for “indivisible”).

• 1897 – J.J Thomson discovered the electron and proposed a model for the structure of atoms.

• 1900 – Max Planck showed that when you vibrate atoms, such as when you heat a material, you can measure the energy in discrete units, which he called quanta.

• 1905 – Albert Einstein explained that light absorption can release electrons from atoms, a phenomenon called photoelectric effect.

• 1911 – Ernest Rutherford experimented on bombarding atoms with alpha rays and he found out that alpha particles went smoothly through the foil, and only occasional alpha particles veered away from its original path. He thought that negative electrons orbited a positive center just like planets orbit the sun.

• 1912 - Niels Bohr theorized that an atom consists of a central nucleus of positive charge around which tiny negatively charged electrons revolve in fixed orbits (Bohr’s Theory), that electrons can only orbit at a certain distance from the nucleus, and that an atom radiates energy when an electron jumps from a higher energy orbit to a lower energy orbit.

• 1919 – Ernest Rutherford identified particles of the nucleus as discrete positive chargesof matter which he called protons (from Greek word “first”). He also found proton mass at 1,836 times as great as the mass of electron.

• 1932 -James Chadwick discovered the neutron.

Atomic Structure• Atoms are the tiniest particles of elements.• An atom consists of a central nucleus of positive charge, around which

negatively charged electrons revolve.• The nucleus of an atom is made up of protons which are positively charged,

and neutrons which are electrically neutral (no charge).• The differences between elements is the number and arrangement of protons,

neutrons, and electrons in their atoms.• Each element has a certain number of electrons and protons.• An electron has a radius of about 10-15 meter and is more than twice as big as a

proton.• An electron has a mass of about 9.11 x 10-28 grams.• A proton is heavier than an electron (around 1840 times heavier than electrons)• A neutron has about the same mass as a proton.• Practically the entire weight of an atom is made up of the weights of the

protons and neutrons.• Atomic weight is the sum of the number of protons and neutrons in the

nucleus of an atom.• Atomic number is equal to the number of electrons revolving around the

nucleus or the number of protons within the nucleus.• Number of neutrons = atomic weight – atomic number

Atomic Structure• The positive charge on each proton (+1.602 x10-19 C) is equal in magnitude to

the negative charge on each electron (-1.602 x10-19 C).• The number of electrons in an atom is equal to the number of protons in the

atom.• An atom is electrically neutral in its stable state (number of electrons =

number of protons).• The orbits of electrons are arranged in “shells” about the nucleus.• Each “shell” has a definite maximum capacity of electrons.• The capacity of successive shells from the nucleus out is 2, 8, 18, 32, 18, 18,

and 2 electrons.• The outermost shell contains not more than 8 electrons.• The outermost shell determines the chemical valence and physical

characteristics of an atom. • The outermost shell is the only one from which electrons are easily dislodged

to become “free” electrons.• The number of electrons in an incomplete outermost unfilled shell is called

valence electrons.• The valence electrons determine if an atom can easily give or gain electrons,

and thus if the element could react with other elements.

Atomic Structure• Trivalent elements have three valence electrons.• Tetravalent elements have four valence electrons.• Pentavalent elements have five valence electrons.• Hydrogen has the simplest atomic structure, having an atomic number of 1

(one electron and one proton).• Some elements such as Helium are chemically inert and could not react with

other elements because they could not share electrons with other elements. Their outermost shell are completely filled up with maximum possible number of electrons.

• Elements could have different number of neutrons, but the number of electrons and protons is always the same. Differing number of neutrons result to various types of isotopes for a given element.

• Different number of neutrons for an element results to different atomic weights for the element, but each element has one particular isotope that is most often found in nature.– Example is Carbon could have an atomic weight of 12 (C12) or 14 (C14).

• Chemical compounds are formed when different elements join together to share electrons. Compounds are different from ordinary mixture of elements.

Atomic Structure• Molecules are the particles which result when atoms of elements join together

to form a chemical compound.• The natural form of elements is also its molecule. An example is two atoms of

oxygen can combine to form a molecule.

Free Electrons• Free electrons are electrons dislodged from the outer shell of an atom. • Free electrons may exist by themselves such as electrons moving from one

metal plate to another plate.• Free electrons constitute the electric current in a conductor.• Many substances contain a number of free electrons, which could move from

one atom to another atom.• Materials capable of having many free electrons, and which could carry

electric current, are called conductors.• Materials which are only capable of having very few free electrons are called

insulators. • Materials which are capable of having not so many free electrons are called

semiconductors. Semiconductors are also capable of carrying electric current.• The more free electrons there are in a material, the better it will conduct.• There are no perfect conductors or insulators.• When a battery is connected across a conductor, free electrons will move in an

orderly fashion towards the positive terminal of the battery.

Ions• An ion is an atom or molecule that has become charged or electrically

unbalanced, due to the loss or gain of electrons.• A positive ion (cation) is an atom or molecule that has lost an electron/s.• A negative ion (anion) is an atom or molecule that has gain an electron/s.• Ionization does not change the chemical properties of an atom but it produces

an electrical change.

Electron Emission• Electrons may leave a certain material through the process of electron

emission.• To enable electrons to leave a certain material, they must perform a certain

amount of work to overcome the restraining forces, and they must be imparted sufficient energy to do this work.

• The energy which could be imparted to electrons may be in the form of heat, light, electric or magnetic fields, or kinetic energy from particles colliding with the electrons.

• The four principal methods of obtaining electron emission from a certain material are:

1. Thermionic emission (primary) – a material which is usually a metal is heated to increase the kinetic energy of unbound (free) electrons, to allow them to escape the surface of the material. The higher is the temperature of the material, the higher is the

number of electrons which could escape. This is the most commonly used in vacuum tubes such as cathode ray

tubes (CRTs) and pentodes.

Electron Emission2. Photoelectric emission – a material is exposed to light radiation and

light energy (quanta) is transferred to the electrons on the material to enable them to escape the surface of the material.

3. Field emission (cold-cathode emission or antoelectronic emission ) – a material is subjected to a strong electric field (i.e., a high positive voltage) to dislodge electrons from the surface of the material. Negatively charged electrons are attracted towards the positive side

of the field. The higher is the electric field intensity, the higher is the number of

electrons which could be dislodged.4. Secondary emission – electrons are dislodged after colliding with high

speed electrons which strike a material. Kinetic energy from the high speed electrons are transferred to the

dislodged electrons. The dislodged electrons are called secondary emission electrons.

Vacuum Tubes

Prepared by: Armando V. Barretto

Vacuum Tubes• One of the most useful electronic device ever used is the vacuum tube. • Vacuum tubes are no longer widely used, but a certain type of tube which

uses more or less the same principle as the vacuum tube, is still used to a great extent. This tube is the cathode ray tube (CRT) which is used in televisions and computer monitors.

• There are many types and uses of vacuum tubes.• During 1904 to 1947, the vacuum tube was the electronic device mostly

used in electronics.• The vacuum tube diode (two elements also called Fleming tube) was

introduced by J. A. Fleming in 1904. Vacuum tube diodes can be used to convert ac voltages to dc voltages.

• The vacuum tube triode (three elements) was introduced by Lee De Forest in 1906. The triode can be used to amplify (increase the amplitude) of signals. He called it an “audion”.

• In early 1930s, the vacuum tube tetrode (4 elements) and vacuum tube pentode (5 elements) were introduced.

• On December 23, 1947, the transistor which replaces the vacuum tubes in many applications, was introduced by Walter H. Brattain and John Bardeen at Bell Telephone laboratories.

Vacuum Tube Diode• The vacuum tube diode is the simplest of all vacuum tubes, but its applications

are not the same as the others.• Below are schematic symbols and construction of a vacuum tube diode.

Vacuum Tube Diode Construction With Cathode

Used As Heater

Source: http://www.answers.com/ topic/vacuum-tube

Anode

Cathode Filament (heater)

Vacuum Tube Diode Schematic Symbol (Separate Heater)

Anode

Cathode

Vacuum Tube Diode Schematic Symbol

Vacuum Tube Diode• The vacuum tube diode has two elements (electrodes) which are:

1. Cathode (also called emitter) – is the main source of electronic emission. The cathode is heated directly (cathode is the heater) or indirectly

(using separate heating element called filament ) to induce electron emission, in the form of thermionic emission.

2. Anode (also called plate or collector) – the electrons emitted from the cathode could be attracted to the anode depending on the polarity and intensity of applied voltage between the anode and the cathode. If the anode is positive enough with respect to the cathode,

electrons which has escaped the surface of the cathode will be attracted towards the anode.

If the voltage between the anode and cathode is zero, or if the voltage of the anode is negative with respect to the cathode, electrons at the cathode will not be attracted towards the anode.

• Both electrodes are enclosed in a vacuum glass or metal, and are attached to conductors which are extended to the outer portion of the enclosure to serve as connection points to the circuit.

• The enclosure is made a vacuum to prevent the collision of electrons with other particles, and to prevent oxidation of the filament.

Vacuum Tube Diode• A relatively small voltage is applied to the filament to heat up the cathode.• A vacuum tube diode can be used as a rectifier to convert ac voltages to dc

voltages. Many electronic devices use dc voltages instead of ac voltages as power supplies.

• Below is a circuit diagram of a rectifier using a vacuum tube diode and a filter using a capacitor (C1).

t

Secondary Voltage (AC)

tRectifier Output Without Capacitor

(Pulsating DC)

Vp

Vp

AK

C1 RL

SecondaryPrimary

Transformer

220 volts ac

t

Vp

Filter Output (DC Voltage With Lower Ripple)

+

-

Electron flow

Conventional Current Flow

Vp=peak voltage of secondary

Vacuum Tube Diode• The transformer is typically used to step down the primary voltage to a lower

voltage at the secondary.• The vacuum tube diode is used to convert the ac voltage at the secondary to a

pulsating dc voltage (positive voltage with ripple).• During the positive half of the secondary voltage, the anode is positive with

respect to the cathode, and electrons at the cathode are attracted to the anoderesulting to a current flow in the direction indicated.

• The electron flow is opposite to the conventional current flow.• During the negative half of the secondary voltage, the anode is negative with

respect to the cathode and electrons at the cathode are not attracted towards the anode. There is no current flow across the diode and the output of the rectifier is 0 volt.

• The capacitor C1 is used as a filter that converts the pulsating dc voltage at the output of the rectifier to an almost pure dc voltage.

• During the positive half of the secondary voltage, the vacuum tube diode conducts and there is current flow. The capacitor is charged with the indicated polarity (positive at the top).

• During the negative half of the secondary voltage, the vacuum tube diode does not conduct and there is no current flow across the diode. The capacitor discharges through the load, thus continuing the supply of current to the load RL.

Vacuum Tube Triode• The vacuum tube triode (audion) is the simplest vacuum tube which could

be used to amplify (increase the amplitude) of signals.• Below are schematic symbols, construction, and a picture of a vacuum tube

triode. Anode

CathodeFilament (heater)

Vacuum Tube Triode Construction With Cathode

Used As Heater

Vacuum Tube Triode Schematic Symbol (Separate Heater)

Vacuum Tube Triode Source:

http://www.answers.com/topic/vacuum-tube

Source: http://www.answers.com/topic/vacuum-tube

Anode

Cathode

Vacuum Tube Triode Schematic Symbol

Control Grid

Control Grid

Vacuum Tube Triode• The vacuum tube triode has three elements (electrodes) which are:

1. Cathode (also called emitter) – is the main source of electronic emission. The cathode is heated directly (cathode is the heater) or indirectly (using

separate heating element called filament ) to induce electron emission, in the form of thermionic emission.

2. Anode (also called plate or collector) – the electrons emitted from the cathode could be attracted to the anode depending on the polarity and intensity of applied voltage between the anode and the cathode, and the voltage at the control grid. It typically has a large positive voltage relative to cathode. If the anode is positive enough with respect to the cathode, electrons which

has escaped the surface of the cathode could be attracted towards the anode depending on the polarity and intensity of the voltage at the control grid.

If the voltage between the anode and cathode is zero, or if the voltage of the anode is negative with respect to the cathode, electrons at the cathode will not be attracted towards the anode.

3. Control Grid – is used to control the electron flow from cathode to anode. It is placed between the cathode and the anode and therefore has greater

effect on the electric field within the tube. Its construction is in such a way that many electrons could pass through it

and reach the anode (assuming anode is positive relative to cathode).

Vacuum Tube Triode The control grid voltage is usually made negative with respect to the

cathode. If the control grid voltage is made less negative, more electrons will

be attracted towards the anode (assuming anode is positive relative to cathode).

If the control grid voltage is made more negative, less electrons will be attracted towards the anode (assuming anode is positive relative to cathode).

The control grid voltage, although it could be varying, is usually not made positive with respect to the cathode to prevent control grid current and distortion of the output signal.

By varying the control grid voltage, the anode current and the anode to cathode voltage can be varied to a great extent.

There is a certain negative voltage at the control grid in which the anode current becomes zero, even though the anode is positive relative to the cathode.

The smallest negative voltage between the control grid and the cathode that is capable of cutting off the anode (plate) current is called cutoff bias.

Vacuum Tube Triode• Below is a circuit wherein a vacuum tube triode is used as an amplifier.

Cc2

VAC

A

K

G

VO = Output voltage

RA

VBB

RLVs =

Source voltage

- VGG

Basic Vacuum Tube Triode Amplifier

VGC

Vi=Vs = input voltage

0 v

-VGG

0 v VsVs is superimposed on - VGG.

VACQ

0 v

VAC VAC = Unfiltered output voltage

VGC

0 v

VOVo = Filtered output voltage

Vacuum Tube Triode• -VGG is used to make the voltage at the control grid negative with respect to

the cathode. • If the control grid is made positive with respect to the cathode, electrons from

the cathode will be attracted to the control grid , anode current can reach saturation point, and tube could be damaged.

• +VBB is used to make the voltage at the anode positive relative to the cathode,so that electrons at the cathode could be attracted towards the anode.

• The input signal (Vs) is an ac signal and it adds to, or subtracts from, the supply voltage -VGG. The peak voltage of the input signal (Vs) is not made larger than -VGG to

prevent the control grid from becoming positive relative to the cathode. During the positive half of the input signal (Vs), the control grid becomes

less negative relative to the cathode. More electrons from cathode are attracted towards the anode. No electrons are attracted towards the control grid because it is still negative relative to the cathode.

During the negative half of the input signal (Vs), the control grid becomes more negative relative to the cathode. Less electrons from cathode are attracted towards the anode. No electrons are attracted towards the control grid because it is negative relative to the cathode.

Vacuum Tube Triode• The variations in electron flow from cathode to anode produces variations in

the current across RA . The variations in current flow across RA produces variations in the voltage across RA and across the anode and cathode.

• Small variations in the input signal (Vs) produces large variations in the voltage across RA and across the anode and cathode, thus amplifying the input signal.

• The voltage relationships at the output loop can be expressed as:

• The output voltage (Vo) is 1800 out of phase with input voltage (Vs).• C1 is used to filter out the dc voltage between the anode and cathode.Note:• When electrons hit the anode, secondary emissions can take place and a cloud

of electrons can be produced inside the tube. The cloud of electrons is called space charge.

• The space charge, having a negative charge, repels electrons from the cathode.

AA

AC

ARA

AA BB AC

ACAA ACRABB

R acrosscurrent current anodeI cathode and anode across voltageV

R across voltageV :whereRI-VV

VRI VVV

Vs electrons IA VAC VO

+

Vacuum Tube Tetrode• The vacuum tube tetrode is similar to a vacuum tube triode except it has an

additional electrode (screen grid) to improve the performance of the vacuum tube.

• Below are schematic symbols of a vacuum tube tetrode.

• The screen grid is placed between the anode and the control grid.• The screen grid is used to reduce the capacitance between the anode and

the control grid because the capacitance could cause unwanted oscillations in the circuit. The capacitance serves as a feedback path for signals.

• The screen grid is made positive with respect to the cathode.

Anode

CathodeFilament (heater)

Vacuum Tube TetrodeSchematic Symbol (Separate Heater)

Anode

Cathode

Vacuum Tube TetrodeSchematic Symbol

Control GridControl Grid

Screen Grid Screen Grid

Vacuum Tube Pentode• The vacuum tube pentode is similar to a vacuum tube tetrode except it has

an additional electrode (suppressor grid) to improve the performance of the vacuum tube.

• Below are schematic symbols of a vacuum tube pentode.

• The suppressor grid is placed between the anode and the screen grid. • The electrons hitting the anode produces secondary emissions and these

electrons could go to the screen grid and reduce the anode current if the suppressor grid is not present.

• The suppressor grid is usually directly connected to the cathode so that electrons due to secondary emissions will be repelled back to the anode.

Anode

CathodeFilament (heater) Vacuum Tube Pentode

Schematic Symbol (Separate Heater)

Anode

Cathode

Vacuum Tube Pentode Schematic Symbol

Control Grid Control Grid

Screen Grid Screen GridSuppressor Grid Suppressor Grid

Vacuum Tube ParametersThe following are parameters used to describe the characteristics of vacuum tube triodes, tetrodes and pentodes:• Amplification factor- is a measure of how effective is the control grid in

overcoming the electrostatic field produced by the plate, or a measure of how effective is the control grid voltage in determining the plate (anode) current, compared with how effective is the plate voltage in determining the plate (anode) current. It can be computed as:

• DC Plate Resistance – describes the opposition (resistance) of the tube to dc current flowing through the cathode and anode (dc resistance of tube). It can be computed as:

factorion amplificat

constant) Ib(with voltagegrid controlin change small voltage(anode) platein change smallconstant) Ib(with

ΔEcΔEb

resistance plate dccurrent anode voltageanode

IbEbRp

Vacuum Tube Parameters• AC Plate Resistance – is the ratio of a small change in plate voltage to

the change in plate current produced, when the control grid voltage is held constant.

• Transconductance – is the ratio of the small change in plate current to a small change in control grid voltage producing it, when the plate voltageis held constant. It is a measure of how effective is the control gridvoltage in controlling the plate current.

factorion amplificat

constant) Eb(with voltagegrid controlin change small

current anodein change smallconstant) Eb(with ΔEcΔIbgm

resistance plate dc

constant) Ecwith (current anodein change

voltageanodein change small constant) Ecwith (IbEbrp

Vacuum Tube Parameters• The amplification factor, ac plate resistance, and transconductance are

related by the following equations.

gm r

gm Ec / IbEc / Eb

IbEbr

p

p