**Electronic Circuit Analysis – ECA Questions and Answers pdf :-**

### Course syllabus: (JNTU) :-

**UNIT-1: Single Stage Amplifiers :-**

Classification of Amplifiers—Distortion in Amplifiers, Analysis of CE, CC, and CB Configuration with simplified Hybrid Model, Analysis of CE amplifier with Emitter resistance and Emitter follower, Millers theorem and its dual, Design of single stage RC Coupled Amplifier using BJT.

**UNIT-II: Multi stage Amplifiers :-**

Analysis of cascaded RC Coupled BJT Amplifiers, Cascode Amplifiers, Darlington Pair, Different Coupling Schemes used in Amplifiers—RC Coupled Amplifier, Transformer Coupled Amplifier, Direct Coupled Amplifier.

**UNIT-III: BJT Amplifiers—Frequency Response :-**

Logarithms, Decibels, General Frequency Response Considerations, Frequency response of BJT Amplifier, Analysis at Low Frequency & High Frequency response of Amplifier, Effect of Coupling & bypass Capacitors. The hybrid pi-Common Emitter Transistor Model. CE Short circuit current Gain, Current Gain with Resistive load, Single Stage CE Transistor Amplifier Response, Gain Bandwidth Product. Emitter follower at higher Frequencies.

**UNIT-IV: MOS Amplifiers :-**

Basic Concepts on MOS Amplifiers, MOS Small signal Model, Common Source Amplifier with resistive load. Diode Connected load for MOS Small Signal Model. Current Source load for MOS Small Signal Model. Source Follower of MOS Amplifiers, Common Gate Stage Cascode Amplifiers. Common gate Stage folded Cascade Amplifier. Cascade Amplifier & their Frequency Response.

**UNIT-V: Feedback Amplifiers :-**

Concepts of Feed Back Amplifiers. Classification of Feed Back Amplifiers, General characteristics of Negative Feed Back Amplifiers. Effect of Feed Back on Amplifier Characteristics, Voltage Series, Voltage Shunt Feedback Configurations. Current Series & Current shunt Feedback Configurations. Illustrative Problems.

**UNIT-VI: Oscillators :-**

Classification of Oscillators, Conditions of Oscillations in Oscillators. RC Phase shift Oscillator, Generalized Analysis of LC Oscillators. Wien-Bridge & crystal oscillators. Stability of Oscillators.

**UNIT-VII: Large Signal Amplifiers :-**

Classification, Class A Large Signal Amplifiers, Transformer Coupled Class A Audio Power Amplifiers, Efficiency of Class A Amplifiers, Class B Amplifier, Efficiency of Class B Amplifiers, Class-B Push-Pull Amplifier, Complimentary Symmetry Class B Push Pull Amplifier, Distortion in Power Amplifiers, Thermal Stability and Heat Sinks.

**UNIT-VIII: Tuned Amplifiers :-**

Introduction, Q-Factor, Small Signal Tuned Amplifiers, Effect of Cascading Single Tuned Amplifiers on Band width, Effect of cascading Double Tuned Amplifiers on Bandwidth, Stagger Tuned Amplifiers, Stability of Tuned Amplifiers.

**1. Relevant Syllabus for GATE & IES :-**

**Amplifiers:** single-and multi-stage, feedback, and power Amplifiers. Frequency response of amplifiers.

**Oscillators:** Classification of Oscillators, RC Phase shift Oscillator, Wien-Bridge & crystal oscillators. Stability of Oscillators.

**Large Signal & Tuned Amplifiers:** Class A Large Signal Amplifiers Class-B Push-Pull Amplifier, Distortion in Power Amplifiers, Thermal Stability and Heat Sinks. Small Signal Tuned Amplifiers, Stagger Tuned Amplifiers, Stability of Tuned Amplifiers.

**Course Text Books and References:**

1. Integrated Electronics—by Jacob Millman and Christos C Halkias, 1991

2. Electronic Circuit Analysis–by S Salivahanan & N Suresh Kumar,2010

3. Design of Analog CMOS Integrated Circuits- Beehzad Razavi, 2008, TMH.

**Reference Books:**

Electronic Devices and Circuit Theory—Robert l. Boylestad, Louis Nashelsky, 2008 PE.

Principles of Electronic Circuits – S.G.Burns and P.R.Bond, Galgotia Publications, 2nd edn.., 1998.

Electronic Circuit Analysis—K, Lal Kishore, 2004, BSP.

Electronic Devices and Circuits – Dr. K. Lal Kishore, B.S. Publications, 2nd Edition, 2005.

5. Electronic Devices and Circuits- David A,Bell—5 ed. Oxford University Press.

**Reference books For Gate :-**

–> Electronic devices and circuits by Millman and Halkias

–> Integrated Electronics by Millman and Halkias

–> Electronic devices and circuits by Boylestad and Nashelsky

–> Microelectronics by Millman and Grabel

**QUESTION BANK :-**

**UNIT-I**

1. a) For the CB amplifier circuit, compute RIN and ROUT if C1 is

i) Connected ii) not connected. The h-parameters of the transistor in CE Configuration

Are listed as: hie = 2.1KΩ, hfe = 81, hoe = 1.66 μMhos and hre is negligibly small.

b) Reason out the causes and results of Phase & Frequency distortions in transistor amplifiers.

2. (a) For the CE circuit, estimate A i, Av, Ri & Ro using reasonable approximations.

The h parameters for the transistor are given as hfe = 100, hie = 2k, hre is negligible

and hoe = 10.5 mhos.

(b) Draw the circuit diagram of Emitter follower and derive the equation for Voltage & current gains.

3. For the amplifier circuit with partially un bypassed emitter resistance, calculate the voltage gain with R4 in place and with R4 shorted. Consider hie = 1.1KΩ, hfe = 100, hre & hoe are negligibly small. Assume R1 and R2 to be 100KΩ and 22 KΩ respectively.

4. For the common emitter amplifier, draw the AC and DC load lines. Determine the peak-to-peak output voltage for a sinusoidal input voltage of 30mV peak-to-peak. Assume C1, C2 and C3 are large enough to act as short circuit at the input frequency. Consider hie = 1.1KΩ, hfe = 100, hre & hoe are negligibly small.

5. Draw the simplified hybrid model for the CC circuit and derive expressions for input Resistance, output resistance voltage gain and current gain.

**UNIT-II**

1. a) Differentiate between direct and capacitive coupling of multiple stages of amplifiers.

b) With the help of a neat circuit diagram, describe the working of a cascade amplifier.

c) What are merits & demerits of a cascade amplifier over a Common Emitter amplifier?

2. a) With the help of circuit diagram and equivalent circuit of a Darlington amplifier

Generate the expression for the overall input impedance of the pair.

b) Develop a generalized expression for overall current gain (AIS) when two transistor

Stages with ROUT2 < RL, ROUT1 > RIN2, RIN1> RS and individual voltage gains are AV1, AV2.

3. a) Derive expressions for overall voltage gain and overall current gain of a two-stage

RC coupled amplifier.

b) List out the special features of Darlington pair and cascade amplifiers.

**UNIT-III**

1. a) Derive the expressions for hybrid Π conductance, gce, and gbb’ of a transistor.

b) Explain how hybrid Π parameters, gm and gce vary with Ic, Vce and temperature.

c) Compute the overall lower cut-off frequency of an identical two stage cascade of

Amplifiers with individual lower cut-off frequency given as 432 Hz.

2. a) A transistor amplifier in CE configuration is operated at high frequency with the following specifications. fT=6MHz, gm=0.04,hfe =50, rbb’ =100 Ω, Rs =500 Ω , Cb’c =10pF, RL=100 Ω.

Compute the voltage gain, upper 3dB cut-off frequency, and gain bandwidth product (GBW)

b) Derive an expression for the overall higher cut-off frequency of a two stage amplifier

With identical stages of individual higher cut-off frequency, fH.

3. a) Discuss the effect of emitter bypass capacitor and input & output coupling capacitors on

The lower cut-off frequency if numbers of amplifiers are cascaded.

b) Describe how an emitter follower behaves at high frequencies.

4. a) A transistor has fα = 8MHz, and β=80.when connected as an amplifier, it has stray capacitance of 100pF at the output terminal. Calculate its upper 3dB frequency when Rload is i) 10KΩ ii) 100KΩ.

b) Discuss the effect of coupling capacitors of a CE amplifier on the overall frequency response of the amplifier.

5. (a) Explain why the upper 3-dB frequency for current gain is not the same as fH for voltage gain.

(b) A Silicon PNP transistor has an f= 400MHz. What is the base thickness?

(c) In terms of what parameters is the high frequency response of a CE stage obtained?

**UNIT-IV**

1. a) Discuss the effect of different type of loads to a common source MOS amplifier.

b) Differentiate between cascade and folded cascade configurations.

2. Derive the equation for voltage gain of a Common Source FET amplifier.

3. (a) Sketch the circuit of a CS amplifier. Derive the expression for the voltage gain at low

Frequencies. What is the maximum value of voltage gain?

(b) The FET shown in figure 5 has the following parameters: IDSS = 5.6mA & VP = –

4V. If Vi = 10V and VO.

4. Derive an expression for voltage gain of a common source FET amplifier with and without source resistance included in the circuit.

5. (a) Why a FET cannot be explained with h-parameters?

(b) Derive an expression for Trans – conductance using FET model.

**UNIT-V**

1. a) An amplifier has a gain of 50 with negative feedback. For a specified output voltage, if the input required is 0.1V without feedback and 0.8V with feedback, Compute β and open loop gain.

b) Through the block schematics, show four types of negative feedback in amplifiers.

c) List the advantages of negative feedback in amplifiers.

2. a) The β and the open loop gain of an amplifier are -10% and -80 respectively. By how much % the closed loop gain changes if the open loop gain increases by 25%?

b) Compare the characteristics of feedback amplifiers in all the four configurations.

c) Reason out why 2 stages are required to implement current shunt feedback.

3. (a) What are the characteristics of an amplifier that are modified by negative feedback?

(b) Draw the four types of feedback amplifiers naming them.

(c) Define sensitivity & De-sensitivity factors in feedback Amplifiers.

4. (a) Discuss about the types of negative feedback amplifiers giving the effect of each type of feedback on the parameters of the amplifier.

(b) What sort of feedback is employed in a CE amplifier with unbypassed emitter resistor? Discuss its analysis in detail.

5. Derive an expression for the transfer gain of a feedback amplifier.

**UNIT-VI**

1. (a) Derive an expression for frequency of oscillation of a RC phase-shift oscillator using

a FET.

(b) In a Hartley oscillator L2 = 0.04 mH and C = 0.004 µF. If the frequency of oscillation

is 150 KHz, and Neglect mutual inductance.

2. a) Differentiate between RC and LC type oscillators.

b) Derive the expression for frequency of oscillation in a Hartley Oscillator.

c) State Barkhausen Criterion for Oscillations

3. a) Substantiate the requirement of positive feedback in amplifier for oscillations. Relate the requirement to Barkhausen Criterion.

b) With the help of neat circuit diagram, explain how sustained oscillations are obtained in RC phase shift BJT based oscillator. Derive the expression fo frequency of oscillation

4. a) Differentiate between RC and LC type oscillators.

b) Derive the expression for frequency of oscillation in a Hartley Oscillator.

c) State Barkhausen Criterion for Oscillations

5. starting from the description of a generalized oscillator, derive the expression for

Frequency of oscillation in a colpits oscillator.

**UNIT-VII**

1. a) A single stage class A amplifier Vcc=20V, VCEQ =10V, ICQ =600mA, RL=16 Ω. The ac

output current varies by 300mA, with the ac input signal. Find ±

i) The power supplied by the dc source to the amplifier circuit.

ii) AC power consumed by the load resistor.

iii) AC power developed across the load resistor.

iv) DC power wasted in transistor collector.

v) Overall efficiency

vi) Collector efficiency.

b). List the advantages of complementary-symmetry configuration over push pull

configuration.

2. a) Derive the expression for maximum conversion efficiency for a simple series fed Class A power amplifier.

b) What are the drawbacks of transformer coupled power amplifiers?

c) A push pull amplifier utilizes a transformer whose primary has a total of 160 turns

and whose secondary has 40 turns. It must be capable of delivering 40W to an 8Ω

load under maximum power conditions. What is the minimum possible value ofVcc?

3. a) With the help of a suitable circuit diagram, show that the maximum conversion

efficiency of a class B power amplifier is 78.5%.

b) Explain how Total harmonic distortion can be reduced in a Class B push-pull

configured amplifier.

4. a) State the merits of using push pull configuration? Describe the operation of class B

push pull amplifier and show how even harmonics are eliminated.

b) A single ended class A amplifier has a transformer coupled load of 8 Ω. If the

transformer turns ratio is 10, find the maximum power output delivered to the

load. Take the zero signal collector current of 500mA.

5 (a) what is push-pull configuration and how does this circuit reduce the harmonic

Distortion?

(b) For a class B amplifier providing a 20V peak signal to a 16 load operates on a

power supply of Vcc = 30V. Determine the input power, output power and

circuit efficiency.

**UNIT-VIII**

1. a) Derive the expressions for Bandwidth and Q-factor of single tuned, capacitively coupled amplifiers. List the assumptions made for the derivation.

b) What is stagger tuning? Suggest possible applications.

2. a) Derive an expression for the bandwidth of a synchronous tuned circuit.

b) Discuss the necessity of stabilization circuits in tuned amplifiers.

3. a) List possible configurations of tuned amplifiers.

b) Derive an expression for bandwidth of a capacitive coupled tuned amplifier in CE

configuration. Make necessary assumptions and mention them.

4. Describe the following briefly:

a) Stagger Tuned Amplifiers – Operation and comparison with synchronous tuning

b) Heat Sinks for tuned power amplifiers.

5. (a) Compare Neutralisation and Unilaterlisation methods of tuned amplifiers.

(b) What are the limitations of stagger tuned amplifiers?

(c) What happens when no. of stages is increased in single tuned cascaded amplifiers?

**Other Important Questions :-**

**Other Important Questions :-**

1. (a) Using the h-parameter model, derive expressions for current gain, input

Impedance, voltage gain and output impedance of a CE amplifier.

(b) The h-parameters of a transistor are hfe=50, hie=1.1KΩ, hre=2.5×10-4,hoe=24μA/V.

Calculate AI, AV, Ap, AVS, Ri and Ro

2. If six identical RC coupled amplifiers are cascaded each having f1 = 100 Hz, determine

the overall f1(n).

3. State Miller’s theorem. Explain its significance in transistor circuit analysis.

4. Using the approximate h-parameter model, derive expressions for current gain, voltage gain, input resistance and output admittance of a CE amplifier with resistor in emitter circuit.

5. Derive the theoretical expressions for f1(n) and f2(n) when n-stages of Identical amplifiers are cascaded.

6. (a) Explain the effect of coupling capacitor and bypass Capacitor in two stage RC

Couple Amplifier

(b) When 2-stages of identical CE Amplifiers are cascaded, obtain the expressions for

Overall Voltage gain, current gain and power gain.

7. For a given single stage amplifier, f2 = 100 KHz, if 8 stages are cascaded. Determine the Overall Cut-off frequency f2.

8. Draw the circuit diagram of CB amplifier circuit and its h-parameter equivalent circuit. List out the characteristics of a CB amplifier.

9. Classify amplifier circuits based on frequency range, type of coupling, power delivered and Signal handled.

10. Write a short note on Bandwidth of Amplifier.

11. Draw the circuit diagram of two Stage Transformers coupled Amplifier and explains its working.

12. Comparison between RC Coupled, Transformer Coupled and Direct Coupled Amplifiers.

13. Draw the equivalent hybrid –pi circuit for the calculation of the short circuit CE current gain. Derive the same

14. Derive the expression for FT and Fβ of CE amplifier using HF Model (hybrid – pi model).

15. Draw the hybrid – pi model for a transistor in the CE configuration. Derive the hybrid-pi Conductance in CE configuration.

16. Sketch CS amplifier using JFET and draw its small signal equivalent circuits.

17. Derive the expression for Av,Ri and Ro for CD JFET amplifier.