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Electronic Circuits 10CS
Dept. of CSE, SJBIT 1
ELECTRONIC CIRCUITS
Subject Code: 10CS32 I.A. Marks : 25 Hours/Week : 04 Exam Hours: 03 Total Hours : 52 Exam Marks: 100
PART - A UNIT – 1 7 Hours
Transistors, UJTs, and Thyristors: Operating Point, Common-EmitterConfiguration, Thermal Runaway, Transistor Switch, Unijunction Transistors, SCR.
UNIT – 2 6 Hours Field Effect Transistors: Bipolar Junction Transistors versus Field Effect Transistors, Junction Field Effect Transistors, Metal Oxide Field Effect Transistors, Differences between JFETs and MOSFETs, Handling MOSFETs, Biasing MOSFETs, FET Applications, CMOS Devices, Insulated Gate Bipolar Transistors (IGBTs)
UNIT – 3 6 Hours Optoelectronic Devices: Introduction, Photosensors, Photoconductors, Photodiodes, Phototransistors, Light-Emitting Diodes, Liquid Crystal Displays, Cathode Ray Tube Displays, Emerging Display Technologies, Optocouplers
UNIT – 4 7 Hours Small Signal Analysis of Amplifiers: Amplifier Bandwidth: General Frequency Considerations, Hybrid h-Parameter Model for an Amplifier, Transistor Hybrid Model, Analysis of a Transistor Amplifier using complete h- Parameter Model, Analysis of a Transistor Amplifier Configurations using Simplified h- Parameter Model (CE configuration only), Small-Signal Analysis of FET Amplifiers, Cascading Amplifiers, Darlington Amplifier, Low-Frequency Response of Amplifiers (BJT amplifiers only).
PART – B UNIT - 5 6 Hours Large Signal Amplifiers, Feedback Amplifier: Classification and characteristics of Large Signal Amplifiers, Feedback Amplifiers: Classification of Amplifiers, Amplifier with Negative Feedback, Advantages of Negative Feedback, Feedback Topologies, Voltage-Series (Series-Shunt) Feedback, Voltage-Shunt (Shunt-Shunt) Feedback, Current-Series (Series- Series) Feedback, Current-Shunt (Shunt- Series)Feedback.
Electronic Circuits 10CS
Dept. of CSE, SJBIT 2
UNIT - 6 7 Hours Sinusoidal Oscillators, Wave-Shaping Circuits: Classification of Oscillators, Conditions for Oscillations: Barkhausen Criterion, Types of Oscillators, Crystal Oscillator, Voltage-Controlled Oscillators, Frequency Stability. Wave- Shaping Circuits: Basic RC Low-Pass Circuit, RC Low-Pass Circuit as Integrator, Basic RC High-Pass Circuit, RC High-Pass Circuit as Differentiator, Multivibrators, Integrated Circuit (IC) Multivibrators.
UNIT - 7 7 Hours Linear Power Supplies, Switched mode Power Supplies: Linear Power Supplies: Constituents of a Linear Power Supply, Designing Mains Transformer; Linear IC Voltage Regulators, Regulated Power Supply Parameters. Switched Mode Power Supplies: Switched Mode Power Supplies, Switching Regulators, Connecting Power Converters in Series, Connecting Power Converters in Parallel.
UNIT - 8 6 Hours Operational Amplifiers: Ideal Opamp versus Practical Opamp, Performance Parameters, Some Applications: Peak Detector Circuit, Absolute Value Circuit, Comparator, Active Filters, Phase Shifters, Instrumentation Amplifier, Non-Linear Amplifier, Relaxation Oscillator, Current-To- Voltage Converter, Voltage-To-Current Converter, Sine Wave Oscillators.
Text Book:
- Anil K Maini, Varsha Agarwal: Electronic Devices and Circuits, Wiley, 2009. (4.1, 4.2, 4.7, 4.8, 5.1 to 5.3, 5.5, 5.6, 5.8, 5.9, 5.13, 5.14, 6.1, 6.3, 7.1 to 7.5, 7.10 to 7.14, Listed topics only from 8, 10.1, 11, 12.1, 12.2, 12.3, 12.5, 13.1 to 13.6, 13.9, 13.10, 14.1, 14.2, 14.6, 14.7, 15.1, 15.5 to 15.7. 16.3, 16.4, 17.12 to 17.22)
Reference Books:
- Jacob Millman, Christos Halkias, Chetan D Parikh: Millman‟s Integrated Electronics – Analog and Digital Circuits and Systems, 2nd Edition, Tata McGraw Hill, 2010.
- R. D. Sudhaker Samuel: Electronic Circuits, Sanguine-Pearson
- Electronic Circuits 10CS
- Dept. of CSE, SJBIT
- Unit – 1: Transistor, UJT‟s, and Thyristors - 1.1 Operating Point - 1.2 The Common Emitter (CE) Configuration - 1.3 The Transistor as a Switch - 1.4 Silicon-Controlled Rectifiers, or SCRs - 1.5 The Gate Turn-Off Thyristors (GTO) - 1.6 Recommended Questions
- Unit – 2: Bipolar Junction Transistors.................................................................................. - 2.1 Bipolar junction transistor (BJT) - 2.2 The Field Effect Transistor - 2.3 The Junction Field Effect Transistor - 2.4 Comparison of connections between a JFET and a BJT.............................................. - 2.5 JFET Amplifier - 2.6 CMOS - 2.7 Recommended Questions
- Unit – 3: Photodiodes - 3.1 Photodiodes - 3.2 PN Photodiode - 3.3 PIN Photodiode - 3.4 Schottky Photodiode - 3.5 Phototransistors - 3.6 Light-Emitting Diodes (LED) - 3.7 Cathode Ray Tube Displays - 3.8 Emerging Display Technologies - 3.9 Optocouplers - 3.10 Recommended Questions
- UNIT – 4: Small Signal Analysis of Amplifiers - 4.1 Basic FET Amplifiers - 4.2 THE MOSFET AMPLIFIER - 4.3 Small-Signal Equivalent Circuit - 4.4 Problem-Solving Technique: MOSFET AC Analysis - 4.5 Basic Transistor Amplifier Configurations - 4.6 The Source-Follower Amplifer
- Dept. of CSE, SJBIT - 4.7 Input and Output impedance - 4.8 The Common-Gate Configuration - 4.9 The Three Basic Amplifier Configurations: Summary and Comparison - 4.10 Recommended Questions
- Unit – 5: Large Signal Amplifiers - 5.1 Classification of Large Signal Amplifiers................................................................. - 5.2 Large signal Amplifier Characteristics - 5.3 Feedback Amplifiers - 5.4 Stability of Gain Factor - 5.5 Feedback Topologies - 5.6 Recommended Questions
- UNIT – 6: Sinusoidal Oscillators - 6.1 Principles of oscillators - 6.2 Phase shift Oscillator - 6.3 Band Pass Oscillators............................................................................................... - 6.4 Wien Bridge Oscillator - 6.5 Colpitts and Hartley Oscillators - 6.6 Piezoelectric Crystal Oscillators............................................................................... - 6.7 Recommended Questions
- UNIT – 7: Linear Power Supplies, Switched mode Power Supplies - 7.1 Regulated power supply - 7.2 POWER SUPPLY FILTER - 7.3 Fixed Positive Linear Voltage Regulators - 7.4 The Regulated Dual Voltage DC Power Supply - 7.5 Recommended Questions
- UNIT – 8: Operational Amplifier....................................................................................... - 8.1 Operational Amplifier (Op-Amp) - 8.2 Ideal Op-Amp - 8.3 Applications of Opamp - 8.4 Instrumentation Amplifier - 8.5 Relaxation Oscillator - 8.6 Current-to-Voltage Converter - 8.7 Voltage-to-Current Converter - 8.8 Exercise Problems
Electronic Circuits 10CS
Dept. of CSE, SJBIT 5
Unit – 1: Transistor, UJT’s, and Thyristors
In the Diode tutorials we saw that simple diodes are made up from two pieces of semiconductor material, either silicon or germanium to form a simple PN-junction and we also learnt about their properties and characteristics. If we now join together two individual signal diodes back-to-back, this will give us two PN-junctions connected together in series that share a common P or N terminal. The fusion of these two diodes produces a three layer, two junctions, and three terminal devices forming the basis of a Bipolar Junction Transistor , or BJT for short.
1.1 Operating Point
Operating Regions
The pink shaded area at the bottom of the curves represents the "Cut-off" region while the blue area to the left represents the "Saturation" region of the transistor. Both these transistor regions are defined as:
1. Cut-off Region
Here the operating conditions of the transistor are zero input base current (IB), zero output collector current (IC) and maximum collector voltage (VCE) which results in a large depletion layer and no current flowing through the device. Therefore the transistor is switched "Fully- OFF".
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Dept. of CSE, SJBIT 7
Then we can define the "saturation region" or "ON mode" when using a bipolar transistor as a switch as being, both junctions forward biased, IB > 0.7V and IC = Maximum. For a PNP transistor, the Emitter potential must be positive with respect to the Base.
Then the transistor operates as a "single-pole single-throw" (SPST) solid state switch. With a zero signal applied to the Base of the transistor it turns "OFF" acting like an open switch and zero collector current flows. With a positive signal applied to the Base of the transistor it turns "ON" acting like a closed switch and maximum circuit current flows through the device.
An example of an NPN Transistor as a switch being used to operate a relay is given below. With inductive loads such as relays or solenoids a flywheel diode is placed across the load to dissipate the back EMF generated by the inductive load when the transistor switches "OFF" and so protect the transistor from damage. If the load is of a very high current or voltage nature, such as motors, heaters etc, then the load current can be controlled via a suitable relay as shown.
Transistor
Transistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage. The transistor's ability to change between these two states enables it to have two basic functions: "switching" (digital electronics) or "amplification" (analogue electronics). Then bipolar transistors have the ability to operate within three different regions:
- Active Region - the transistor operates as an amplifier and Ic = β.Ib
- Saturation - the transistor is "fully-ON" operating as a switch and Ic = I(saturation)
- Cut-off - the transistor is "fully-OFF" operating as a switch and Ic = 0
Typical Bipolar Transistor
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The word Transistor is an acronym, and is a combination of the words Transfer Varistor used to describe their mode of operation way back in their early days of development. There are two basic types of bipolar transistor construction, PNP and NPN, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made.
The Bipolar Transistor basic construction consists of two PN-junctions producing three connecting terminals with each terminal being given a name to identify it from the other two. These three terminals are known and labeled as the Emitter ( E ), the Base ( B ) and the Collector ( C ) respectively.
Bipolar Transistors are current regulating devices that control the amount of current flowing through them in proportion to the amount of biasing voltage applied to their base terminal acting like a current-controlled switch. The principle of operation of the two transistor types PNP and NPN, is exactly the same the only difference being in their biasing and the polarity of the power supply for each type.
Bipolar Transistor Construction
The construction and circuit symbols for both the PNP and NPN bipolar transistor are given above with the arrow in the circuit symbol always showing the direction of "conventional current
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more importantly "load" resistance (RL) to "input" resistance (Rin) giving it a value of "Resistance Gain". Then the voltage gain (Av) for a common base configuration is therefore given as:
Common Base Voltage Gain
Where: Ic/Ie is the current gain, alpha (α) and RL/Rin is the resistance gain.
The common base circuit is generally only used in single stage amplifier circuits such as microphone pre-amplifier or radio frequency (Rf) amplifiers due to its very good high frequency response.
1.2 The Common Emitter (CE) Configuration
In the Common Emitter or grounded emitter configuration, the input signal is applied between the base, while the output is taken from between the collector and the emitter as shown. This type of configuration is the most commonly used circuit for transistor based amplifiers and which represents the "normal" method of bipolar transistor connection. The common emitter amplifier configuration produces the highest current and power gain of all the three bipolar transistor configurations. This is mainly because the input impedance is LOW as it is connected to a forward-biased PN-junction, while the output impedance is HIGH as it is taken from a reverse-biased PN-junction.
The Common Emitter Amplifier Circuit
In this type of configuration, the current flowing out of the transistor must be equal to the currents flowing into the transistor as the emitter current is given as Ie = Ic + Ib. Also, as the load resistance (RL) is connected in series with the collector, the current gain of the common emitter transistor configuration is quite large as it is the ratio of Ic/Ib and is given the Greek symbol of Beta, (β). As the emitter current for a common emitter configuration is defined as Ie = Ic + Ib,
Electronic Circuits 10CS
Dept. of CSE, SJBIT 11
the ratio of Ic/Ie is called Alpha, given the Greek symbol of α. Note: that the value of Alpha will always be less than unity.
Since the electrical relationship between these three currents, Ib, Ic and Ie is determined by the physical construction of the transistor itself, any small change in the base current (Ib), will result in a much larger change in the collector current (Ic). Then, small changes in current flowing in the base will thus control the current in the emitter-collector circuit. Typically, Beta has a value between 20 and 200 for most general purpose transistors.
By combining the expressions for both Alpha, α and Beta, β the mathematical relationship between these parameters and therefore the current gain of the transistor can be given as:
Where: "Ic" is the current flowing into the collector terminal, "Ib" is the current flowing into the base terminal and "Ie" is the current flowing out of the emitter terminal.
Then to summarize, this type of bipolar transistor configuration has a greater input impedance, current and power gain than that of the common base configuration but its voltage gain is much lower. The common emitter configuration is an inverting amplifier circuit resulting in the output signal being 180o^ out-of-phase with the input voltage signal.
The Common Collector (CC) Configuration
In the Common Collector or grounded collector configuration, the collector is now common through the supply. The input signal is connected directly to the base, while the output is taken from the emitter load as shown. This type of configuration is commonly known as a Voltage Follower or Emitter Follower circuit. The emitter follower configuration is very useful for impedance matching applications because of the very high input impedance, in the region of hundreds of thousands of Ohms while having a relatively low output impedance.
The Common Collector Transistor Circuit
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Then to summarize, the behavior of the bipolar transistor in each one of the above circuit configurations is very different and produces different circuit characteristics with regards to input impedance, output impedance and gain whether this is voltage gain, current gain or power gain and this is summarized in the table below.
Bipolar Transistor Characteristics
The static characteristics for a Bipolar Transistor can be divided into the following three main groups.
Input Characteristics:- Common Base - ΔVEB / ΔIE Common Emitter - ΔVBE / ΔIB
Output Characteristics:- Common Base - ΔVC / ΔIC Common Emitter - ΔVC / ΔIC
Transfer Characteristics:- Common Base - ΔIC / ΔIE Common Emitter - ΔIC / ΔIB
With the characteristics of the different transistor configurations given in the following table:
Characteristic Common Base
Common Emitter
Common Collector Input Impedance Low Medium High Output Impedance Very High High Low Phase Angle 0 o^180 o^0 o Voltage Gain High Medium Low Current Gain Low Medium High Power Gain Low Very High Medium
In the next tutorial about Bipolar Transistors , we will look at the NPN Transistor in more detail when used in the common emitter configuration as an amplifier as this is the most widely used configuration due to its flexibility and high gain. We will also plot the output characteristics curves commonly associated with amplifier circuits as a function of the collector current to the base current.
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The NPN Transistor
In the previous tutorial we saw that the standard Bipolar Transistor or BJT, comes in two basic forms. An NPN (Negative-Positive-Negative) type and a PNP (Positive-Negative-Positive) type, with the most commonly used transistor type being the NPN Transistor. We also learnt that the transistor junctions can be biased in one of three different ways - Common Base , Common Emitter and Common Collector. In this tutorial we will look more closely at the "Common Emitter" configuration using NPN Transistors with an example of the construction of a NPN transistor along with the transistors current flow characteristics is given below.
An NPN Transistor Configuration
(Note: Arrow defines the emitter and conventional current flow, "out" for an NPN transistor.)
The construction and terminal voltages for an NPN transistor are shown above. The voltage between the Base and Emitter ( VBE ), is positive at the Base and negative at the Emitter because for an NPN transistor, the Base terminal is always positive with respect to the Emitter. Also the Collector supply voltage is positive with respect to the Emitter (VCE). So for an NPN transistor to conduct the Collector is always more positive with respect to both the Base and the Emitter.
NPN Transistor Connections
Then the voltage sources are connected to an NPN transistor as shown. The Collector is connected to the supply voltage VCC via the load resistor, RL which also acts to limit the maximum current flowing through the device. The Base supply voltage VB is connected to the Base resistor RB, which again is used to limit the maximum Base current.
Electronic Circuits 10CS
Dept. of CSE, SJBIT 16
The values of Beta vary from about 20 for high current power transistors to well over 1000 for high frequency low power type bipolar transistors. The value of Beta for most standard NPN transistors can be found in the manufactures datasheets but generally range between 50 - 200.
The equation above for Beta can also be re-arranged to make Ic as the subject, and with a zero base current ( Ib = 0 ) the resultant collector current Ic will also be zero, ( β x 0 ). Also when the base current is high the corresponding collector current will also be high resulting in the base current controlling the collector current. One of the most important properties of the Bipolar Junction Transistor is that a small base current can control a much larger collector current. Consider the following example.
Example No
An NPN Transistor has a DC current gain, (Beta) value of 200. Calculate the base current Ib required to switch a resistive load of 4mA.
Therefore, β = 200, Ic = 4mA and Ib = 20μA.
One other point to remember about NPN Transistors. The collector voltage, ( Vc ) must be greater and positive with respect to the emitter voltage, ( Ve ) to allow current to flow through the transistor between the collector-emitter junctions. Also, there is a voltage drop between the Base and the Emitter terminal of about 0.7v (one diode volt drop) for silicon devices as the input characteristics of an NPN Transistor are of a forward biased diode. Then the base voltage, ( Vbe ) of a NPN transistor must be greater than this 0.7V otherwise the transistor will not conduct with the base current given as.
Where: Ib is the base current, Vb is the base bias voltage, Vbe is the base-emitter volt drop (0.7v) and Rb is the base input resistor. Increasing Ib, Vbe slowly increases to 0.7V but Ic rises exponentially.
Example No
An NPN Transistor has a DC base bias voltage, Vb of 10v and an input base resistor, Rb of 100kΩ. What will be the value of the base current into the transistor.
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Therefore, Ib = 93μA.
The Common Emitter Configuration
As well as being used as a semiconductor switch to turn load currents "ON" or "OFF" by controlling the Base signal to the transistor in ether its saturation or cut-off regions, NPN Transistors can also be used in its active region to produce a circuit which will amplify any small AC signal applied to its Base terminal with the Emitter grounded. If a suitable DC "biasing" voltage is firstly applied to the transistors Base terminal thus allowing it to always operate within its linear active region, an inverting amplifier circuit called a single stage common emitter amplifier is produced.
One such Common Emitter Amplifier configuration of an NPN transistor is called a Class A Amplifier. A "Class A Amplifier" operation is one where the transistors Base terminal is biased in such a way as to forward bias the Base-emitter junction. The result is that the transistor is always operating halfway between its cut-off and saturation regions, thereby allowing the transistor amplifier to accurately reproduce the positive and negative halves of any AC input signal superimposed upon this DC biasing voltage. Without this "Bias Voltage" only one half of the input waveform would be amplified. This common emitter amplifier configuration using an NPN transistor has many applications but is commonly used in audio circuits such as pre- amplifier and power amplifier stages.
With reference to the common emitter configuration shown below, a family of curves known as the Output Characteristics Curves , relates the output collector current, (Ic) to the collector voltage, (Vce) when different values of Base current, (Ib) are applied to the transistor for transistors with the same β value. A DC "Load Line" can also be drawn onto the output characteristics curves to show all the possible operating points when different values of base current are applied. It is necessary to set the initial value of Vce correctly to allow the output voltage to vary both up and down when amplifying AC input signals and this is called setting the operating point or Quiescent Point, Q-point for short and this is shown below.
Single Stage Common Emitter Amplifier Circuit
Output Characteristics Curves of a Typical Bipolar Transistor
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Then, the collector or output characteristics curves for Common Emitter NPN Transistors can be used to predict the Collector current, Ic, when given Vce and the Base current, Ib. A Load Line can also be constructed onto the curves to determine a suitable Operating or Q-point which can be set by adjustment of the base current. The slope of this load line is equal to the reciprocal of the load resistance which is given as: -1/RL
Then we can define a NPN Transistor as being normally "OFF" but a small input current and a small positive voltage at its Base (B) relative to its Emitter (E) will turn it "ON" allowing a much large Collector-Emitter current to flow. NPN transistors conduct when Vc is much greater than Ve.
In the next tutorial about Bipolar Transistors , we will look at the opposite or complementary form of the NPN Transistor called the PNP Transistor and show that the PNP Transistor has very similar characteristics to their NPN transistor except that the polarities (or biasing) of the current and voltage directions are reversed.
The PNP Transistor
The PNP Transistor is the exact opposite to the NPN Transistor device we looked at in the previous tutorial. Basically, in this type of transistor construction the two diodes are reversed with respect to the NPN type giving a Positive-Negative-Positive configuration, with the arrow which also defines the Emitter terminal this time pointing inwards in the transistor symbol.
Also, all the polarities for a PNP transistor are reversed which means that it "sinks" current as opposed to the NPN transistor which "sources" current. The main difference between the two types of transistors is that holes are the more important carriers for PNP transistors, whereas electrons are the important carriers for NPN transistors. Then, PNP transistors use a small output base current and a negative base voltage to control a much larger emitter-collector current. The construction of a PNP transistor consists of two P-type semiconductor materials either side of the N-type material as shown below. A PNP Transistor Configuration
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(Note: Arrow defines the emitter and conventional current flow, "in" for a PNP transistor.)
The construction and terminal voltages for an NPN transistor are shown above. The PNP Transistor has very similar characteristics to their NPN bipolar cousins, except that the polarities (or biasing) of the current and voltage directions are reversed for any one of the possible three configurations looked at in the first tutorial, Common Base, Common Emitter and Common Collector.
PNP Transistor Connections
The voltage between the Base and Emitter ( VBE ), is now negative at the Base and positive at the Emitter because for a PNP transistor, the Base terminal is always biased negative with respect to the Emitter. Also the Emitter supply voltage is positive with respect to the Collector ( VCE ). So for a PNP transistor to conduct the Emitter is always more positive with respect to both the Base and the Collector.
The voltage sources are connected to a PNP transistor are as shown. This time the Emitter is connected to the supply voltage VCC with the load resistor, RL which limits the maximum current flowing through the device connected to the Collector terminal. The Base voltage VB which is biased negative with respect to the Emitter and is connected to the Base resistor RB, which again is used to limit the maximum Base current.
To cause the Base current to flow in a PNP transistor the Base needs to be more negative than the Emitter (current must leave the base) by approx 0.7 volts for a silicon device or 0.3 volts for a germanium device with the formulas used to calculate the Base resistor, Base current or Collector current are the same as those used for an equivalent NPN transistor and is given as.
Generally, the PNP transistor can replace NPN transistors in most electronic circuits, the only difference is the polarities of the voltages, and the directions of the current flow. PNP transistors can also be used as switching devices and an example of a PNP transistor switch is shown below.
