2. BASIC ELECTRONICS
COURSE OBJECTIVES:
To understand the characteristics of diodes and transistor configurations.
2.To understand the design concepts of biasing of BJT and FET.
3.To understand the design concepts of feedback amplifiers and
oscillators.
4. To study the design concepts of OP Amp and data converters
characteristics of FETs, MOSFETs and study IC fabrication techniques.
MATRUSRI
ENGINEERING COLLEGE
3. BASIC ELECTRONICS
MATRUSRI
ENGINEERING COLLEGE
COURSE OUTCOMES:
On successful completion of this course, the students will be able to:
1.Study and analyse the rectifier and regulator circuits.
2.Study and analyse the performance of BJTs, FETs on the basis of their
operation and working.
3.Ability to analyse and design oscillator circuits.
4.Ability to analyse different logic gates and multivibrator circuits.
5.Ability to analyse different data acquisition systems.
4. UNIT-III
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Feedback concepts: Types of negative feedback-modification of gain ,
bandwidth , input and output impedances-applications
Oscillators : RC phase shift ,Wien bridge , LC and Crystal oscillators
(Qualitative treatment only).
OUTCOMES:
Analyse the importance of positive and negative feedback
mechanisms.
Understand & Analyse General Characteristics & applications of
Negative Feedback Amplifiers.
Analyse effect of negative feedback on Input & Output Resistance of
various amplifiers.
Able to understand conditions for a circuit to work as an oscillator.
Understand & Analyse the Qualitative analysis of RC, LC & Crystal
Oscillators.
5. MATRUSRI
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OUTCOMES:
Analyse the importance of positive and negative feedback
mechanisms.
Understand & Analyse General Characteristics &
applications of Negative Feedback Amplifiers.
Analyse effect of negative feedback on Input & Output
Resistance of various amplifiers.
MODULE-I
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CONTENTS:
Importace of Feedback concepts
Types of negative feedback
modification of gain , bandwidth , input and output
impedances
applications
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Introduction
• Feedback plays an important role in electronic circuits where some part
of the output is fed back to the input through a feedback network. So at
the input side there is source and feedback signals.
• When the source signal is in phase with feedback signal, it is called as
positive feedback.
• When the source signal is out of phase with feedback signal, it is called
as negative feedback.
• Negative feedback employed in amplifying the signals and positive
feedback is employed in oscillator circuits.
• An oscillator is an electronic circuit which employs a positive feedback
where the source signal and feedback signal both are in phase.
• These oscillators are used to generate oscillations which can be sine or
triangular or rectangular waves.
7. VOLTAGE AMPLIFIER:
Here the output voltage is proportional to input voltage and at both i/p
and o/p of circuis we have thevenin circuits
Vo = AVVi , RL>> Ro, Ri>>RS
Classification of Amplifiers
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8. CURRENT AMPLIFIER
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In current amplifier, o/p current is directly proportional to input
current. It maintains Norton equivalent circuit at both i/p and o/p.
Io = AIII , RL<<Ro, Ri<<RS
9. TRANS CONDUCTANCE AMPLIFIER
In trans conductance amplifier the o/p current depends on i/p voltage, it
has thevenin equivalent at i/p and Norton equivalent t o/p.
IL = GMVi , RL<<Ro, Ri>>RS
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10. TRANS RESISTANCE AMPLIFIER
In this amplifier, o/p voltage depends on i/p current, at i/p it has Norton
equivalent and o/p it has thevenin equivalent.
VO=RMII RL>>Ro, Ri>>RS
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11. BLOCK DIAGRAM OF FEEDBACK AMPLIFIER
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sampling network
A sampling network samples some part of the output signal
and connected to input through feedback network. Depending
on type sampling quantity, we have two types, they are
a) Voltage sampling b) Current Sampling
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Mixer or Comparator :
It is used to connect the feedback signal at the input circuit.
There are two types of mixing circuits.
1. Series Mixing 2. Shunt Mixing
14. Classification of negative feedback amplifiers
Based on Sampling network and mixer, negative feedback
amplifiers are classified into
1) Voltage Series Feedback Amplifier
2) Voltage Shunt Feedback Amplifier
3) Current Series Feedback Amplifier
4) Current Shunt Feedback Amplifier
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General Characteristics of Negative Feedback Amplifiers
Transfer Gain
Gain of an amplifier without feedback is A = Xo/Xi
Gain of an amplifier with feedback is Af = Xo/Xs
The output of mixer is Xi = Xs – Xf
Xs = Xi + Xf
Af = Xo/ (Xi+Xf)
= (Xo/Xi)/(1+Xf/Xi) = A/(1+Xf/Xo*Xo/Xi)
24. MATRUSRI
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OUTCOMES:
Able to understand conditions for a circuit to work as an
oscillator.
Understand & Analyse the Qualitative analysis of RC, LC
& Crystal Oscillators.
MODULE-II
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CONTENTS:
Introduction
Classifications of Oscillators
Circuit Analysis of a General Oscillator
Conditions for Oscillation: Barkhausen- Criteria
RC , LC Oscillators
Crystal Oscillator
Applications of Oscillators
25. MATRUSRI
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INTRODUCTION
Oscillator is a circuit/ electronic system that produce a continuous
signal/waveform on its output with only the dc supply voltage as an input.
The output voltage can be either sinusoidal or non sinusoidal depending on
the type of oscillator.
• It comprises active and passive circuit elements and sinusoidal produces
repetitive waveforms at the output without the application of a direct
external input signal to the circuit.
• It converts the dc power from the source to ac power in the load. A
rectifier circuit converts ac to dc power, but an oscillator converts dc
noise signal/power to its ac equivalent.
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Difference between an amplifier and an oscillator
Need of an Oscillator:
An oscillator circuit is capable of producing ac voltage of desired
frequency and waveshape.
To test performance of electronic circuits, it is called signal generator.
It can produce square, pulse, triangular, or sawtooth waveshape.
High frequency oscillator are used in broadcasting.
Microwave oven uses an oscillator.
Used for induction heating and dielectric heating.
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Using Positive Feedback
•The gain with positive feedback is given as
•By making 1 – Aβ = 0, or Aβ = 1, we get gain as infinity.
• This condition (Aβ = 1) is known as Barkhausen Criterion of oscillations.
• It means you get output without any input !
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Conditions for Oscillation
•Phase shift around the feedback loop must be 0o or 360o
•Voltage gain, Acl, around the closed feedback loop (loop gain)
must equal 1 (unity) – The voltage gain around the closed
feedback loop (Acl) is the product of amplifier gain (Av) and the
attenuation (B) of the feedback circuit
Acl = Av B
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Start-Up Conditions
•For oscillation to begin, Acl around the positive feedback loop
must be greater than 1so that the output voltage can build up
to a desired level.
•Then Acl decrease to 1 and maintains the desired magnitude
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Wherefrom comes the starting voltage ?
• Each resistor is a noise generator.
• The feedback network is a resonant circuit giving maximum
feedback voltage at frequency f0, providing phase shift of 0°
only at this frequency.
• The initial loop gain Aβ > 1.
• The oscillations build up only at this frequency.
• After the desired output is reached, Aβ reduces to unity.
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CLASSIFICATIONS OF OSCILLATORS
Oscillators are classified based on the type of the output waveform.
• If the generated waveform is sinusoidal or close to sinusoidal (with a
certain frequency) then the oscillator is said to be a Sinusoidal
Oscillator.
• If the output waveform is non-sinusoidal, which refers to square/saw-
tooth waveforms, the oscillator is said to be a Relaxation Oscillator.
• An oscillator has a positive feedback with the loop gain infinite.
Feedback-type sinusoidal oscillators can be classified as LC (inductor-
capacitor)(Hartley ,Colpitts Oscillator) and RC (resistor-capacitor)
oscillators ( RC phase shift Oscillator, Wien bridge Oscillator).
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• A phase shift oscillator has a single amplifier where output
is connected to a feedback network which consists of 3
sections of RC networks connected in a ladder type with
each section producing 600 phase shift.
• So ,all the 3 sections of the network produces 1800 phase
shift and the output of this feedback is applied to the input
of the amplifier.
• As the amplifier produces 1800 phase shift and feedback
n/w also producing 1800 .the total phase shift around the
loop is 3600 which satisfies barkhausen condition to
generate oscillations.
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A wein bridge oscillator consists of a two stage amplifier
where theo/p of the amplifier is applied to a feedback
network which has series RC and parallel RC networks which is
leag-lag network. A two stage amplifier introduces a phase
shift of 00 or 3600 and a feedback network also introduce 00
phase shift due to lead-lag nature of the circuit. So, total
phase shift around the circuit is 00 which satisfies barkhausen
condition to generate the oscillations.
f = 1/2πRC
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LC Oscillators
• Consider a charged capacitor placed across a inductor which has a
electrostatic energy.
• After sometime the capacitor discharges in clockwise direction and
generates flow of current which magnetizes the inductor.
• So, electrostatic energy is converted into magnetic energy and when
there is maximum magnetic energy the electrostatic energy is 0.
• After some time the magnetic energy collapses by generating current
which charges the capacitor in opposite polarity.
• Under maximum electrostatic energy there is no magnetic energy. This
process is repeated and generates oscillations.
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Frequency Stability of an Oscillator
For an oscillator, the freq of oscillations must be constant. The
measure of ability of an oscillator to maintain the desired frequency
as precisely as possible for long time is called “Frequency Stability of
an Oscillator”
The following are the factors which affects the stability of an
oscillator.
1) Due to changes in temperature the values of a component of a
tank circuit (LC Circuit) gets affected. So changes in the values of an
inductor and capacitor due to change in temp is the main cause of
deviation in the frequency.
2) Due to changes in temp, the parameters of a active devices like
BJT, FET gets affected.
3) The variation in power supply is another factor affecting the
frequency.
4) The changes in the atmosphere conditions, aging and unstable
transistor parameters affect the frequency
5) The capacitive affect in the transistor and stray capacitances
effects the capacitances of tank circuits and hence the frequency
49. MATRUSRI
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Long Answer Questions
1. Draw Hartley Oscillator circuit and explain its principle of operation
and derive its frequency of operation and condition for maintenance
of oscillation.
2. What are the types of feedback amplifiers? Explain the negative
feedback amplifier and obtain its closed loop gain?
3. Draw the circuit diagram of RC phase shift oscillator using BJT and
derive the expression for frequency of oscillations?
4. What are the disadvantages of negative feedback? Explain how the
input and output impedances of an amplifier are effected by the
negative feedback.
5. Explain Wien bridge oscillator with its circuit diagram? Derive
frequency of oscillation and β for the circuit.
6. What are the four different types of negative feedbacks employed in
feedback amplifiers and show these by block diagrams along with
input and output connections.
