Transistor Construction Transistor Operation Common-Base Configuration

Electronics (2)
Dr. Aly Mohamed Gaballa
Faculty of Engineering Sciences
Electronics and Communications Department

Course Description
 Reference Book
Thomas L. Floyd. Electronic Devices (2012), Ninth edition.
Grading scheme
Assignments 10 %
Quizzes 10%
Midterm Exam 30%
Final Exam 50 %
ENE 3106 Electronics (2)
ENE 3106 Electronics (2) 2 Dr. Ali M. Gaballa

 Course Materials
o Prerequisite: ENE 2204
o Multi-stage bipolar transistors amplifiers: small signal amplifier at :
low, mid, and high frequencies .
o Multi-stage unipolar transistor amplifiers, frequency response, Large
signal amplifiers.
o Class A, Class B, class AB, and Class C power amplifiers. Push-pull
amplifiers.
o Differential and operational amplifiers, flip-flops circuits and wave
shaping, introduction to Super-conductivity, introduction to magnetic
and insulation materials.
Course Description

Bipolar Junction Transistor (BJT)
Chapter (1)
Transistor Bias circuits
Chapter (2)
Power Amplifiers
Chapter (3)
Unipolar Transistor Amplifiers
Chapter (4)
Operational Amplifiers
Chapter (5)
 Course Outlines
Course Description
 Course Materials
o Multi-stage Bipolar Transistors Amplifiers: Small Signal Amplifier at :Low, Mid,
and High Frequencies .
o Multi-stage Unipolar Transistor Amplifiers, Frequency Response, Large Signal
Amplifiers.
o Class A, Class B, Class AB, And Class C Power Amplifiers. Push-pull Amplifiers.
o Differential and Operational Amplifiers, Flip-flops Circuits and Wave Shaping,
Introduction to Super-conductivity, Introduction to Magnetic and Insulation
Materials.

4–1 Bipolar Junction Transistor (BJT) Structure
4–2 Basic BJT Operation
4–3 BJT Characteristics and Parameters
4–4 The BJT as an Amplifier
4–5 The BJT as a Switch
4–6 The Phototransistor
Transistor Bias circuits
5–1 The DC Operating Point
5–2 Voltage-Divider Bias
5–3 Other Bias Methods
Power Amplifiers
6–1 Amplifier Operation
6–2 Transistor AC Models
6–3 The Common-Emitter Amplifier
6–4 The Common-Collector Amplifier
6–5 The Common-Base Amplifier
6–6 Multistage Amplifiers
6–7 The Differential Amplifier
Course Description

Special – Purpose Op -Amp Circuits
14–1 Instrumentation Amplifiers
14–2 Isolation Amplifiers
14–3 Operational Trans-conductance Amplifiers (OTAs)
14–4 Log and Antilog Amplifiers
14–5 Converters and Other Op-Amp Circuits
Operational Amplifiers
12–1 Introduction to Operational Amplifiers
12–2 Op-Amp Input Modes and Parameters
12–3 Negative Feedback
12–4 Op-Amps with Negative Feedback
12–5 Effects of Negative Feedback on Op-Amp Impedances
12–6 Bias Current and Offset Voltage
12–7 Open-Loop Frequency and Phase Responses
12–8 Closed-Loop Frequency Response Basic Op-Amp Circuits
13–1 Comparators
13–2 Summing Amplifiers
13–3 Integrators and Differentiators
Course Description

 Why Semiconductors?
o Semiconductors: They are here, there, everywhere and in anything “intelligent”
 Definition
o Electrical elements refer to:
(Resistor (R), Capacitor (C), Inductor (L), Transformer, Voltage Source and Curent
Source.),
o Electronic elements refer to:
Diode Transistors, FET, MOSFET Thyristors, Opto-isolators, Operational Amplifiers,
Power Electronics,
Course Description
o Computers, Laptops
o Cell phones
o CD players
o TV Remotes
o Satellite Dishes
o Fiber Networks
o Traffic Signals, Car taillights
o Air Bag
 Silicon (Si) MOSFETs, ICs, CMOS
 Si ICs, GaAs FETs, BJTs
 AlGaAs and InGaP laser diodes, Si photodiodes
 Light emitting diodes (LEDs)
 InGaAs MMICs (Monolithic Microwave ICs)
 InGaAs P laser diodes, pin photodiodes
 GaN LEDs (green, blue) InGaAsP LEDs (red)
 Si MEMs, Si ICs

Course Description
 Semiconductor devices are widely used

Chapter (1)

Chapter (1) Bipolar Junction Transistor (BJT)
 Definition : Transistors are semiconductor devices that act as either electrically
controlled switches or amplifier controls.
 What are the function of transistor
 Transistor: Transfer resistor
Introduction
 BJT was invented in 1948 at Bell Telephone Laboratories

Amplifier
O/P signal
I/P signal
DC power
 Amplification is the process of linearly increasing the amplitude of an electrical signal and
is one of the major properties of a transistor
BJT Applications
 Amplifiers

 Why do we need to Amplifier? Linear Analog Amplifier
BJT Applications
 Amplifiers

 Switches
o A transistor can be operated as an electronic switch in cutoff and saturation
BJT Applications

NPN BJT switch circuit
Use relay to separate the control circuit from the high current/voltage electrical circuit
BJT Applications
 Switches

 Transistor to Drive the Motor
o A transistor can also used to drive and
regulate the speed of the DC motor in a
unidirectional way by switching the transistor
in regular intervals of time.
o the DC motor is also an inductive load so we
have to place a freewheeling diode across it to
protect the circuit.
o By switching the transistor in cutoff and
saturation regions, we can turn ON and OFF
the motor repeatedly.
o It is also possible to regulate the speed of the
motor from standstill to full speed by
switching the transistor at variable
frequencies. We can get the switching
frequency from control device or IC like
microcontroller.
Control the speed of motor using Pulse Width Modulation
The duty cycle of input digital signal controls the DC level applied to the motor
BJT Applications
 Switches

 Digital Logic
Not Gate AND Gate OR Gate
BJT Applications
 Design of digital logic and memory circuits

o An H-bridge is a transistor-based circuit capable of driving motors both clockwise
and counter-clockwise.
BJT applications
 Switches

 The BJT (bipolar junction transistor) is constructed with three regions: base, collector,
and emitter.
 The BJT has two pn junctions, the base-emitter junction and the base-collector
junction..
 The base region is very thin and lightly doped compared to the collector and emitter
regions.
Chapter (1) Bipolar Junction Transistor (BJT) Bipolar Junction Transistor Structure

 Standard BJT (bipolar junction transistor) symbols.
o The two types of bipolar junction transistor are the npn and the pnp.
Chapter (1) Bipolar Junction Transistor (BJT) Bipolar Junction Transistor Structure

Review: Diode Operation
1 2 2
3 4

Basic BJT Operation
 Biasing

 Operation
Chapter (1) Bipolar Junction Transistor (BJT) Basic BJT Operation

 Operation
Chapter (1) Bipolar Junction Transistor (BJT) Basic BJT Operation
 IB: dc base current
 IE: dc emitter current
 IC: dc collector current
 IE=IC+IB
o Transistor Currents
 Current in a BJT consists of both free electrons and holes, thus the term bipolar.

BJT Characteristics and Parameters
 The dc current gain of a transistor is the ratio of the dc collector current (IC) to the dc base
current (IB) and is designated dc beta (βDC).
 Transistor dc bias circuits.
 Find the relation between α and ß

 BJT Circuit Analysis
o Three transistor dc currents and three dc voltages can be identified.
 IB: dc base current
 IE: dc emitter current
 IC: dc collector current
 VBE: dc voltage at base with respect to emitter
 VCB: dc voltage at collector with respect to base
 VCE: dc voltage at collector with respect to emitter
 Transistor DC Model
Chapter (1) Bipolar Junction Transistor (BJT) BJT Characteristics and Parameters

o Since the emitter is at ground (0 V), by Kirchhoff’s voltage law, the voltage across RB is
o Also, by Ohm’s law,
o The voltage at the collector with respect to the grounded emitter
o Since the drop across RC is
o The voltage at the collector with respect to the emitter can be written as
o The voltage across the reverse-biased collector-base junction is

 Solution

 Some Important Rules
o Rule 1
 For an npn transistor, the voltage at the collector VC must be greater than the voltage at the
emitter VE .
 For pnp transistors, the emitter voltage must be greater than the collector.
o Rule 2
 For an npn transistor, there is a voltage drop from the base to the emitter of 0.7 V.
 For a pnp transistor, there is a - 0.7V rise from base to emitter.
 In terms of operation, this means that the base voltage VB of an npn transistor must be at least
0.7 V greater than the emitter voltage VE; otherwise, the transistor will pass an emitter-to-
collector current.
 For a pnp transistor, VB must be at least 0.7 V less than VE; otherwise, it will not pass a
collector-to emitter current.

 Collector Characteristic Curves
o Input Circuit
o Output Circuit

o Output Circuit

 DC Load Line

 active mode – used for amplification
 cutoff and saturation modes – used for switching.
 Simplified Structure and Modes of Operation

 Example: Determine whether or not the transistor in Figure below is in saturation. Assume VCE(sat) =
0.2 V.

 DC Models (npn)
BJT Characteristics and Parameters

 Example: Consider the circuit shown in Figure below. We wish to analyze this circuit to
determine all node voltages and branch currents. We will assume that β is specified to be 100.

Typical dependence of b on IC and on temperature in a modern integrated-circuit npn silicon transistor
intended for operation around 1 mA.

 Maximum Transistor Ratings
o The maximum ratings are given for collector-to-base voltage, collector-to-emitter voltage,
emitter-to-base voltage, collector current, and power dissipation
o The product of VCE and IC must not exceed the maximum power dissipation. Both VCE and IC
cannot be maximum at the same time.
o If VCE is maximum, IC can be calculated as
o If IC is maximum, VCE can be calculated by rearranging the previous equation as follows:

 Derating PD(max)
PD(max) is usually specified at 25°C. For higher temperatures, PD(max) is less. Datasheets often give
derating factors for determining PD(max) at any temperature above 25°C. For example, a derating
factor of 2 mW/°C indicates that the maximum power dissipation is reduced 2 mW for each degree
Celsius increase in temperature.

The BJT as an Amplifier
o Amplification is the process of linearly increasing the amplitude of an electrical signal and is one
of the major properties of a transistor
o To operate as an amplifier, the base-emitter junction must be forward-biased and the
base-collector junction must be reverse-biased. This is called forward-reverse bias.

The BJT as a Switch
o The second major application area is switching applications. When used as an electronic switch,
a BJT is normally operated alternately in cutoff and saturation. Many digital circuits use the
BJT as a switch.
o Switching Operation
o Conditions in Cutoff (the base-emitter junction is not forward-biased)
o Conditions in Saturation (the base-emitter junction is forward-biased)

The Phototransistor
o In a phototransistor, base current is produced by incident light.
o A phototransistor can be either a two-lead or a three-lead device.
o An opto-coupler consists of an LED and a photodiode or phototransistor.
o Opto-couplers are used to electrically isolate circuits.

Transistor Categories

Chapter (1) Bipolar Junction Transistor (BJT) Transistor Categories

Summary of Bipolar Junction Transistors
o Currents And Voltages
o Symbols

o Switching
o Amplification

o Key Formulas

Summary of BJT Circuits at DC

Transistor Construction Transistor Operation Common-Base Configuration

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