Title font size 44 - Welcome to IARE | IARE, Best ...Small Signal Analysis Of A JunctionTransistor....
Transcript of Title font size 44 - Welcome to IARE | IARE, Best ...Small Signal Analysis Of A JunctionTransistor....
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ELECTRONIC CIRCUIT ANALYSIS
(AEC004)
B.TECH IV semester ECE(AUTONOMOUS-R16)
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UNIT ISINGLE STAGE AMPLIFIERS
AND FREQUENCY RESPONSE
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Classification ofAmplifiers
Type of Signal
Based on No.of
Stages Type of
Configuration
Classification based on Frequency of
conduction angle Operation
Small Signal
Large Signal
Single Stage
Multistage
Common Emitter
Common Base
Common Collector
Class AAmplifier Direct Current (DC)
Class B Amplifier Audio Frequencies (AF)
Class AB Amplifier Radio Frequencies (RF)
VHF, UHF and SHFClass C Amplifier Frequencies
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Different Regions Of Operation
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Transistor Voltage specifications For Various Operating Regions
Condition forActive & Saturation Regions
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TransistorBiasing
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CE, CC, & CBAmplifiers
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H-Parameters Representation Of AnAmplifier
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Hybrid model of CE, CC, & CBAmplifiers
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Small Signal Analysis Of A Junction Transistor
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Small signal analysis of transistor amplifier
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Steps for ac analysis of a transistor circuit
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Design Problem
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Approximate H-Model For CE Amplifier
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Approximate H-Model For CC Amplifier
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Approximate H-Model For CB Amplifier
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Design Problem
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Miller ’s Theorem
Millers theorem is used to simplify the analysis of a
circuit
whenever there is a feedback connection in the circuit
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Analysis Of CEAmplifierWith Unbypassed RE
RE is added to stabilize the gain of the amplifier
RE acts as a feedbackresistor
The overall gain will reduce with unbypassedRE
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AC Equivalent Circuit For CE Amplifier with RE Splittedusing dual of Miller ’s Theorem
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h-Parameter Equivalent Circuit (Exact Analysis)
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h-Parameter Equivalent Circuit (Approximate Analysis)
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Design Parameter
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Design Problems
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HIGH FREQUENCY RESPONSE OF AMPLIFIER
UNIT-II
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The hybrid-π common emitter transistor model
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common emitter short circuit current gain
• The transistors high frequency capability can be known, if is CE S.C forward. Current transfer ratio or current gain is found as function of frequency.
• As RL is socket the approximate. High frequency model becomes as shown in
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1
e
i
h fA
fj
f
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• With a resistive load connected in the output, the high frequency sq ckt of a CE transistor amplifier is shown in fig (a) by using miller’s theorem the ckt of fig (a) can be modified as described below.
• From fig (a) the voltage gain
current gain with resistive load
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• Fig (a) high frequency eq ckt with resistive load since the impedance at the i\p gets decreased by a factor (1-A) the capacitance will be increased by a factor of (1-A) or if .
• The capacitance that is to be included in the o\p ckt will not make any significant change in the performance and may be neglected. This result in the modified eq ckt of fig (b)
• The total i\p capacitance between B & E is
m LA g R
1 1m L
A g R
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1 1
1
1
1
( )S b b b e
S fe
RR
R h
1| |
s s BR R R
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1 12
fe
b e b e
hf
r C
T
fe
ff
h
alpha, beta cut-off frequencies
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• fTis defined as the frequency at which the s.c CE current gain has a magnitude of unity
T fef h f
gain bandwidth product
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• All the resistance components in the hybrid-pi model can be obtained from the h parameters in CE configuration.
1.Transistor Transconductance (gm)= |IC| / VT
2.The Input Conductance (gb1
e )= gm / hfe
3.The Feedback Conductance (gb1
c ) = hre gb1
e
4.The Base Spreading Resistance (rb1
b) = hie - rb1
e
5. The Output Conductance (gce)= hoe-(1+hfe) gb1
c
• There are basically two types of capacitances in pn junction diode i.e. one is junction capacitance and other is diffusion capacitance
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• The active mode BJT has one forward biased pn junction and one reverse biased pn junction. in case of npn BJT the capacitances associated with pn junctions are labeled as
1.Cµ =junction capacitance associate with reversed biased CBJ
2. Cje = junction capacitance associate with forward biased EBJ
3. Cde=diffusion capacitance associate with forward biased EBJ
• The diffusion capacitance and junction capacitance associated with forward biased EBJ are appeared parallel and can be combined as Cπ = Cje + Cde
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MULTI STAGE AMPLIFIERS AND TUNED AMPLIFIERS
UNIT-III
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Need For Cascading
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Block diagram of 2-Stage Cascade Amplifier
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Gain
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Coupling Schemes
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RC coupling
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Transformer coupling
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Direct coupling
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Frequency Response of 2-Stage RC CoupledAmplifier
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Single Tuned Amplifier
•Uses one parallel tuned circuit as the load IZI in each stage and all
these tuned circuits in different stages are tuned to the same
frequency. To get large Av or Ap, multistage amplifiers are used. But
each stage is tuned to the same frequency, one tuned circuit in one
stage.
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Single Tuned Capacitive Coupled Amplifier
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Single Tuned Amplifier
•Uses one parallel tuned circuit as the load IZI in each stage and all
these tuned circuits in different stages are tuned to the same
frequency. To get large Av or Ap, multistage amplifiers are used. But
each stage is tuned to the same frequency, one tuned circuit in one
stage.
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Equivalent circuit of Single Tuned Capacitive
Coupled Amplifier
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Equivalent circuit of Single Tuned Capacitive Coupled Amplifier(applying Miller's Theorem)
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Simplified equivalent circuit
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Simplified output circuit
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Tapped Single Tuned Capacitance Coupled Amplifier
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Equivalent circuit of Tapped Single Tuned Capacitance
Coupled Amplifier
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Single Tuned Transformer Coupled or Inductively Coupled Amplifier
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Single Tuned Transformer Coupled or Inductively Coupled Amplifier
(b)Simplified circuit(a)Equivalent circuit
©Equivalent circuit
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Double Tuned Amplifier
• It uses two inductively coupled tuned circuits, for each stage of the amplifier. Both the tuned circuits are tuned to the same frequency, two tuned circuits in one stage, to get sharp response.
• It provides larger 3-db band width than the single tuned amplifier. Therefore Gain x Bandwidth product is more.
• It provides gain - frequency curve having steeper sides and flatter top.
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Double tuned amplifier circuit
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Stagger Tuned Amplifier
•This circuit uses number of single tuned stages in cascade.
The successive tuned circuits are tuned to slightly different
frequencies.
Variation of Av with f
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UNIT-IV
Feedback Amplifiers & Oscillators
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CLASSIFICATION OF AMPLIFIERS
• Amplifiers can be classified broadly as,
• I. Voltage amplifiers.
• 2. Current amplifiers.
• 3. Transconductance amplifiers.
• 4. Transresistance amplifiers.
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VOLTAGE AMPLIFIER
This circuit is a 2-port network and it represents an amplifier (see in Fig 7.1).Suppose Ri» Rs, drop across Rs is very small.
Equivalent circuit of voltage amplifiers.
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CURRENT AMPLIFIER
•An ideal current amplifier is one which gives output current proportional to input current and•the proportionality factor is independent ofRs and RL.
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TRANSCONDUCTANCE AMPLIFIERIdeal Transconductance amplifier supplies output current which is proportional
to input voltageindependently of the magnitude of Rs and RL.
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TRANS RESISTANCE AMPLIFIERIt gives output voltage Vo proportional to Is, independent of Rs a. RL. For
ideal amplifiers
Rj =0, Ro=O
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GENERALIZED BLOCKSCHEMATIC
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Introduction To Feedback
• The process of injecting a fraction of output energy of some
device back to the input is known as feedback.
• some of the short comings(drawbacks) of the amplifier circuit
are:
1.Change in the value of the gain due to variation in
supplying voltage, temperature or due to components.
2.Distortion in wave-form due to non linearities in the
operating characters of the amplifying device.
3.The amplifier may introduce noise (undesired signals)
• The above drawbacks can be minimizing if we introduce
feedback
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basic types of feedback in amplifiers
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Positive feedback
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Negative feedback.
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CLASSIFACTION OF FEEDBACK AMPLIFIERS
voltage series feedback. Voltage shunt Feedback
Current Shunt Feedback Current Series Feedback
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EFFECT OF NEGATIVE FEEDBACK ON TRANSFER GAIN
REDUCTION IN GAIN
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INCREASE IN BANDWIDTH
REDUCTION IN DISTORTION
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FEEDBACK TO IMPROVE SENSITIVITY
FREQUENCY DISTORTION
BAND WIDTH
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REDUCTION OF NOISE
TRANSFER GAIN WITH FEEDBACK
Consider the generalized feedback amplifier
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LOOP GAIN
Return Ratio
βA = Product of feedback factor β and amplification factor A is called as
Return Ratio.
Return Difference (D)The difference between unity (1) and return ratio is called as Return difference.
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CLASSIFACTION OF FEEDBACK AMPLIFIERS
There are four types of feedback,
1. Voltage series feedback.2. Voltage shunt feedback.
3. Current shunt feedback.4. Current series feedback
voltage series feedback. Voltage shunt Feedback
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Current Series FeedbackCurrent Shunt Feedback
EFFECT OF FEEDBACK ON INPUT RESISTANCE
Voltage shunt Feedback Current Shunt Feedback
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Current shunt feedback.
Equivalent circuit.
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CURRENT SERIES FEEDBACK VOLTAGE SHUNT FEEDBACK
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OSCILLATORS
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There are two types of oscillators circuits:
I. Harmonic Oscillators 2. Relaxation Oscillators
PERFORMANCE MEASURES OF OSCILLATOR CIRCUITS:
Stability: Amplitude stability:
Output Power: Harmonics:
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BARKHAUSEN CRITERION
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R - C PHASE-SHIFT OSCILLATOR
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A GENERAL FORM OF LC OSCILLATOR CIRCUIT
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- Aβ must be positive, and at least unity in magnitude. Than XI and X2 must have the same sign.
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(a) Colpitts oscillator (b) Hartely oscillator circuit
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Wien bridge oscillatorcircuit.
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CRYSTAL OSCILLATORS
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UNIT-V
LARGE SIGNAL AMPLIFIERS
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Transistor Audio Power Amplifier
• A transistor amplifier which raises the power level of the signals that have audio frequency range is known as transistor audio power amplifier.
• A transistor that is suitable for power amplification is generally called a power transistor.
• The typical power output rating of a power amplifier is 1W or more.
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Factors to be considered in large signal
amplifiers:
• Output power
• Distortion Operating
• region Thermal
• considerations
• Efficiency
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Difference Between Voltage and Power
Amplifiers
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Performance Quantities of Power Amplifiers
(i) Collector efficiency
The ratio of a.c. output power to the zero signal power (i.e. d.c. power) supplied by the
battery of a power amplifier is known as collector efficiency.
(ii) Distortion
The change of output wave shape from the input wave shape of an amplifier is known as
distortion.
(iii) Power dissipation capability
The ability of a power transistor to dissipate heat is known as power dissipation
capability.
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Classification of Power Amplifiers
•Class A: It is one, in which the active device conducts for the full 360°.•Class B: Conduction for 180 °.•Class C: Conduction for < 180°.•Class AB :Conduction angle is between 180°. and360°.•Class D: These are used in transmitters because their efficiency is high: 100%.•Class S:Switching regulators are based on class'S' operation.
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Class A power amplifier
•If the collector current flows at all times during the full cycle of the signal,
the power amplifier is known as class A power amplifier.
•If the Q point is placed near the centre a/the linear region a/the dynamic
curve, class A operation results. Because the transistor will conduct for
the complete 360 , distortion is low for small signals and conversion
efficiency is low.
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Types of class-A power Amplifiers
1. Series fed
There is no transformer in the circuit. RL is in series with V cc. There is DC power drop across RL. Therefore efficiency = 25% (maximum).
2. Transformer coupled
• The load is coupled through a transformer. DC drop across the primary of the transformer is
negligible. There is no DC drop across RL. Therefore efficiency = 50% maximum.
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Series Fed class-A power Amplifier
Fig.(a)Series fedClass A power amplifier circuit Fig.(b)Transter curve
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Transformer Coupled class-A power Amplifier
Fig.(a)Transformer Coupled Class A power amplifier circuit Fig.(b)Transfer curve
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Class B power amplifier
• If the collector current flows only during the positive half-cycle of the input signal,
it is called a class B power amplifier.
•For class B operation the Q point is set near cutoff. So outputpower will be
more and conversion efficiency is more. Conduction is only for 180
Transfer curve
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Types of class-B power Amplifiers
• Push-Pull Amplifier
The standard class B push-pull amplifier requires a centre
tapped transformer
• Complimentary Symmetry Circuits
(Transformer Less Class B PowerAmplifier)
Complementary symmetry circuits need only one phase
They don't require a centre tapped transformer.
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Advantages & Disadvantages of Class B power Amplifier
Advantages1.More output power; efficiency = 78.5%. Max.2.Efficiency is higher. Since the transistor conducts only for 180°, when it is not conducting, it will not draw DC current.3.Negligible power loss at no signal. Disadvantages:
4.Supply voltage V cc should have good regulation. Since if Vcc changes, the operating point changes (Since Ic changes).Therefore transistor may not be at cut off.
5.Harmonic distortion is higher. (This can be minimized by pushpull connection).
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Class B Push-Pull Amplifier
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Complimentary Symmetry Circuits (Transformer Less Class B Power Amplifier)
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Differences between class-A & B power
Amplifiers
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Heat Sinks
•The metal sheet that serves to dissipate the additional heat
from the power transistor is known as heat sink.
•The purpose of heat sinks is to keep the operating temperature
of the transistor low, to prevent thermal breakdown.
•Almost the entire heat in a transistor is produced at the
collector-base junction. If the temperature exceeds the
permissible limit, this junction is destroyed and the transistor
is rendered useless.
•Most of power is dissipated at the collector-base junction.
This is because collector-base voltage is much greater than the
base-emitter voltage, although currents through the two
junctions are almost the same.
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High Power Transistor Type.
• re TO-3 and TO-66 types. These are diamond shaped. For
power transistors, usually, the ease itself in the collector
convention and radiation
• Finned aluminium heat sinks yield the best heat transfer per
unit cost.
Fin-type heat sink Power transistor heat sink