EC6401 Electronic circuits II anna university question papers regulation 2013 unit wise EC6401 Electronic circuits II with anna university previous questions regulation 2013 unit wise for 2nd year ece department The questions are segregated unit wise, from past 8 university question papers.

1. EC6401- Electronic circuits -II
Anna University Question Paper (R-2013) all unit wise from 2015 to 2017
-V.U.Dharani kumar, A.P, ECE
PART-A
Unit 1
1. The voltage gain without negative feedback is 40dB. What is the new voltage gain if 3% negative
feedback is introduced? NOV/DEC 17, APR/MAY 15
2. A multipole amplifier having a first pole at 1MHz and an open-loop gain of 100dB is to be
compensated for closed-loop gains as low as 20dB by an introduction of a non-dominant pole. At
what frequency must the pole be placed? NOV/DEC 17
3. What is the effect of negative feedback on noise and bandwidth of an amplifier?
APR/MAY 17, NOV/DEC 16, MAY/JUN 16
4. Mention the three networks that are connected around the basic amplifier to implement feedback
concept? APR/MAY 17
5. An amplifier has an open loop gain of 1000 and a feedback ratio of 0.04. if the open loop gain
changes by 10% due to temperature, find the % change in gain of the amplifier with feedback?
NOV/DEC 16
6. Calculate the voltage gain and output voltage of a negative feedback amplifier with A=120,
β=0.05, and Vs=75mV? MAY/JUN 16
7. A negative feedback amplifier has a bandwidth of 250kHz and de-sensitivity factor of 4. What is
the bandwidth of the basic amplifier without feedback? NOV/DEC 15
8. Draw the magnitude and phase angle plot of three stage amplifier? NOV/DEC 15
9. List out the properties of negative feedback amplifier? APR/MAY 15
Unit 2
1. Give any two examples of high and low frequency oscillators? NOV/DEC 17
2. State Barkhausen criterion? NOV/DEC 17, APR/MAY 17, APR/MAY 15
3. How Barkhausen criterian are satisfied in Twin –T oscillator? NOV/DEC 15
4. In an Hartley oscillator, if L1=0.2 mH, L2=0.3mH and C=0.003µF. Calculate the frequency of
oscillations? APR/MAY 17
5. What are the factors which affect the frequency stability of an oscillator? NOV/DEC 16
6. What are the merits and demerits of an RC phase shift oscillator? NOV/DEC 16, MAY/JUN 16
7. Sketch feedback circuit of Colpitts oscillator. Calculate the value of the equivalent series
capacitance required if it uses an inductance of 100mH and is to oscillate at 40kHz. MAY/JUN 16
8. The quartz crystal has Cm=1pF, Ls=3H, Cs=0.05pF and Rs=1k. Calculate the series and parallel
resonant frequency? NOV/DEC 15
9. Write the feedback factor expression for BJT transistor based Wein Bridge Oscillator? APR/MAY 15
Unit 3:
1. What is the use of transformer in tuned amplifier circuit? NOV/DEC 17
2. Determine the bandwidth of two stage synchronous tuned amplifier. Assume the bandwidth of
individual stages is 200kHz. NOV/DEC 17, APR/MAY 15

2. 3. A tuned circuit has a resonant frequency of 1600kHz and a bandwidth of 10kHz. What is the value
of its Q factor? APR/MAY 17
4. An inductor of 250µH has Q=300 at 1 MHz. Determine Rs and Rp of the inductor. APR/MAY 17
5. List out some advantages of double tuned amplifier. NOV/DEC 16
6. Define Q factor of the capacitor. NOV/DEC 16
7. What is the effect of Q on the resonance circuit? MAY/JUN 16
8. Draw the ideal response and actual response of tuned amplifiers? MAY/JUN 16
9. A 3µH coil used in tuned amplifier tunes to 1050kHz has Rs=50Ω. If the load resistance of the
amplifier is RL=5K. Calculate the loaded and unloaded Q of the tank circuit. NOV/DEC 15
10. What is meant by neutralization? NOV/DEC 15
11. Draw the small signal model of the single tuned amplifier. APR/MAY 15
Unit 4
1. What is the role of commutation capacitor in bistable multivibrator? APR/MAY 15, MAY/JUN 16, NOV/DEC 17
2. Differentiate between clipper and clamper? APR/MAY 15, NOV/DEC 17
3. Why do we call astable multivibrator as free-running multivibrator? APR/MAY 17
4. How can a Schmitt trigger act as a zero crossing detector? APR/MAY 17
5. What are the different types of multivibrator? NOV/DEC 16
6. Mention the uses of Schmitt trigger circuit? NOV/DEC 16
7. An RC low pass circuit has R=1.5kΩ and C=0.2µF. What is the rise time of the output when
excited by a step input? MAY/JUNE 16,
8. Define rise time of a switching transistor? NOV/DEC 15
9. Draw the hysteresis characteristics of the Schmitt trigger circuit? NOV/DEC 15
UNIT 5:
1. Design a second order HPF with identical RC section. Assume the gain is 3, f= 35kHz, C=0.01
microfarad? NOV/DEC 17
2. Differentiate between monostable and astable multivibrator? NOV/DEC 17
3. State any two applications of pulse transformer? APR/MAY 17
4. Determine voltage and current time base circuit? APR/MAY 17
5. Draw the millers circuit to activate the sweep NOV/DEC 16
6. What is intrinsic stand-off ratio and mention its range? NOV/DEC 16
7. What are the different methods used for generation of ramp waveforms? MAY/JUNE 16
8. Give the applications of blocking oscillators? MAY/JUNE 16
9. Application of voltage and current time base circuit? NOV/DEC 15
10. Determine the frequency of oscillation of an UJT relaxation oscillator. Assuming Re=10.7k, Ce=0.22µF and
intrinsic stand-off ratio =0.56. NOV/DEC 15
11. Design an RC circuit to generate an output voltage V0, with a slope error of 20% ans sweep time of 20µs
and sweep voltage of 2V. APR/MAY 15
12. Draw the schematic diagram of free running blocking oscillator. APR/MAY 15

3. PART-B
Unit-1
1. Identify the nature of feedback in below figure let Rc1=3kΩ, Rc2=500Ω, RE=50Ω, Rs=Rf=1.2kΩ, hfe=50,
hie=1.1kΩ, hre=hoe=0. Determine the overall voltage gain (Avf) and overall current gain (Aif).
13m NOV/DEC 17, APR/MAY 15
2. Consider a three pole feedback amplifier with a loop gain given by
Determine the frequency of dominant pole to stabilize the feedback system. Assume the phase margin is at-
least 45o
. 13m NOV/DEC 17, APR/MAY 15
3. Draw the block diagram of current series feedback amplifier and derive an expression for input resistance,
voltage gain and output resistance. Part C (9) NOV/DEC 17, APR/ MAY 17, NOV/DEC 16
4. Draw a two stage voltage series feedback amplifier and its basic amplifier. Derive for Av and Avf with
equivalent circuit. Part C (9) NOV/DEC 17, APR/MAY 15
5. Sketch the block diagram of a feedback amplifier and derive the expressions for gain with positive
feedback and with negative feedback? 9m APR/MAY 17
6. An amplifier has voltage gain with feedback as 100. If the gain without feedback changes by 20% and the
gain with feedback should not vary more than 2%, determine the values of open loop gain A and feedback
ratio β. 4m APR/MAY 17
7. Draw the circuits of voltage shunt feedback amplifiers and derive the expressions for input impedance,
voltage gain and output resistance? 10m APR/MAY 17,
8. Write about the Nyquist criterion for stability of feedback amplifiers? 3m APR/MAY 17
9. Identify feedback topology for the network shown below, which have Rs =600 Ω , hie=5k Ω, hfe=80, RL=2k
Ω, RB=40k Ω. Calculate Av, Rif, Avf, Rof and R’
of. 13m NOV/DEC 16
10. Draw the circuit diagram of a single stage common emitter amplifier that uses emitter current feedback.
Analyse the circuit and derive equations for gain, input and output impedance with feedback.
16m MAY/JUNE 16

4. 11. With the help of neat schematic, discuss the classification of feedback amplifiers. Discuss quantitatively,
the effect of topology of a feedback amplifier on input and output resistance. Also derive the expression for
input and output resistance of shunt-series feedback amplifier. 16m MAY/JUNE 16
12. Draw the basic amplifier of the feedback amplifier shown below. With equivalent circuit of basic amplifier,
derive for its transfer gain and hence find its loop gain: 6m NOV/DEC 15
13. Identify the feedback topology. Find the open and closed loop gain of the circuit given. Assume
hie1=hie2=2K, hfe1=hie2=100. 10 NOV/DEC 15
14. Explain in detail the stability of three pole amplifier. 6 NOV/DEC 15
15. Given the loop gain function T(f)=β(100)/(1+jf/105
)3
, determine the stability of the amplifier for β=0.2 and
β=0.02. 10 NOV/DEC 15
Unit 2:
1. Draw Wein bridge oscillator using BJT, explain and derive the condition for oscillation.13 NOV/DEC 17, NOV/DEC 15
2. In colpitts oscillator C1=1µF and C2=0.2 µF. If the frequency of oscillation is 10kHz, find the value of
inductor. Also find the required gain for sustained oscillations? 3m NOV/DEC 17, APR/MAY 15
3. Draw Hartley oscillator using FET, explain and derive the condition for oscillation? 13m NOV/DEC 17, APR/MAY 15
4. With neat sketch, explain the principle of operation of a Colpitt’s oscillator. Obtain the equation for the
frequency of operation of the circuit? 13m APR/MAY 17, NOV/DEC 15
5. Sketch the circuit of a phase shift oscillator and explain its design approach? 10m APR/MAY 17

5. 6. In a colpitts oscillator, the value of the inductor and capacitors in the tank circuit are L=40mH, C1=100pF
and C2=500pF. Find the frequency of oscillations. 3m APR?MAY 17
7. Derive the general form of frequency of oscillations for LC oscillator with suitable diagram? 16m NOV/DEC 16
8. Enumerate the following: franklin and Armstrong oscillator? 16m NOV/DEC 16, APR/MAY 15
9. Explain the principle of operation of Armstrong oscillator with a neat diagram? 8m MAY/JUNE 16
10. Discuss the operation and principles used in Twin-T oscillators? 8m MAY/JUNE 16
11. Discuss briefly the principles of oscillations in crystals and draw the equivalent circuit, impedance
frequency graph of crystals and give expression or its series and parallel resonant frequency? 8m MAY/JUNE 16
12. Discuss the frequency stability of crystal oscillator? 8m MAY/JUNE 16
13. Design a clap oscillation to generate 12kHz sine wave BJT amplifier with a gain of -110. Given
gm=30mA/V, hfe=150. Draw the designed circuit, Vec=20V 8 NOV/DEC 15
14. Draw RC phase shift oscillator using BJT, explain and derive the condition for oscillation? 10 APR/MAY 15
15. Compare colpitts and clap oscillator. 2 APR/MAY 15
Unit 3:
1. Explain single tuned amplifier and derive for gain and resonant frequency? 13 NOV/DEC 17, NOV/DEC 15, APR/MAY 15
2. Explain the stability of tuned amplifiers using neutralization techniques 9 NOV/DEC 17
3. Explain stagger tuned amplifier with frequency response? 4,6 NOV/DEC 17, APR/MAY 15
4. A tank circuit having a 5mH coil with resistance 22Ω and C=1nF is connected as load to a single tuned
amplifier with R0=10K. Calculate loaded and unloaded Q factor. Part C 6 NOV/DEC 17
5. Draw the circuit of class C tuned amplifier and explain its operation with relevant waveforms. Discuss also
its frequency response. (8) APR/MAY 17, NOV/DEC 15, APR/MAY 15
6. With a neat diagram, explain the Hazeltine method of neutralization. (8)APR/MAY 17, NOV/DEC 16, NOV/DEC 15, APR/MAY 15
7. Draw the circuit of a double-tuned amplifier and explain its operation. Sketch the nature of frequency-gain
characteristics and write the expression for 3-dB bandwidth. (13) APR/MAY 17
8. Design a tuned amplifier using FET to have f0=1MHz, 3 dB bandwidth is to be 10kHz and maximum gain
is to be -10. FET has gm=5mA/V and rd= 10kΩ. Part c 8 APR/MAY 17
9. Discuss the effect of cascading single tuned amplifier on bandwidth. (13) NOV/DEC 16
10. Derive the efficiency of class C tuned amplifier (6) NOV/DEC 16, NOV/DEC 15
11. Consider the design of an IF amplifier for FM radio receiver. Using two synchronously tuned stages with
f0= 10.7MHz and 3 –dB of each stage so that the overall bandwidth is 200kHz. Using 3 µH inductors find
C and R for each stage. 4 APR/MAY 15
Unit 4:
1. Explain the operation of Schmitt trigger with a neat diagram and relevant input and output waveforms?
13m NOV/DEC 17, MAY/JUNE 16
2. Consider the collector coupled monostable multivibrator whose components and supply voltages are
indicated in the below circuit, calculate the voltage levels (VB2,VC2,VC1,VB1) of the waveforms during (t=0-
,0 and T) periods in the graph below. Also find the overshoot voltage δ. Assume silicon transistor having
hfe=50, Vσ=0.7V, VΫ(cut-in)=0.5V and input resistance, 200 Ω. 13m NOV/DEC 17, APR/MAY 15

6. 3. With the help of neat diagram, explain the working of emitter coupled astable multivibrator? 6m NOV/DEC 17
4. Draw the astable multivibrator circuit using BJT to generate a pulse waveform 0-10V at 5KHz with 50%
duty cycle? Part C 6m NOV/DEC 17
5. Design a astable multivibrator circuit to generate a pulse waveforms at 40% duty cycle at 20kHz using
Vcc=10V, hfe=220, Ic(sat) =2mA. Part C 15m APR?MAY 17
6.
7. Sketch a transistor switching circuit and its collector –current response wave form for a pulse input, for
such a circuit, explain the following terms:
i) Delay time,
ii) Turn-on time
iii) Storage time
iv) Fall time
v) Turn-off time. 10m APR/MAY 17, NOV/DEC 15
8. An inductor of 250µH has Q=300 at 1MHz. Determine Rs and Rp of the inductor? 3m APR?MAY 17
9. With a neat circuit diagram and necessary wave forms, explain bistable multivibrator operation.
13m APR?MAY 17
10. Design a saturated collector coupled astable multivibrator for the following specification. Output voltage
12V peak. Output to be positive pulse, the duration is 10µs. The time between pulses to be 20µs, for the
BJT hfe=100, ICBO=0, Ic(on)=1mA, assume VCE(SAT)=0.2V. 16m NOV/DEC 16
11. Explain the operation and working principle of monostable multivibrator with necessary diagram?
16m NOV/DEC 16
12. Explain the following
i) Positive clamper. 5m MAY/JUNE 16
ii) Negative clamper. 5m MAY/JUNE 16
iii) RC differentiator. 6m MAY/JUNE 16
13. Explain clipper and clamper circuit with input and output waveforms. 8 NOV/DEC 15
14. Explain the working of collector coupled astable multivibrator. 16 NOV/DEC 15
Unit V
1. Explain the working principle of voltage time base (sweep) generator in detail? 7 NOV/DEC 17, APR/MAY 15
2. Explain the working principle of current time base (sweep) circuit? 6, 10 NOV/DEC 17, NOV/DEC 15, APR/MAY 15

7. 3. With suitable circuit and waveform diagrams, explain the working of UJT saw tooth generator?
13 NOV/DEC 17, APR/MAY 17, NOV/DEC 16, APR/MAY 15
4. Explain the working principle of free running blocking oscillator? 7 NOV/DEC 17
5. Draw the circuit of an astable blocking oscillator with base timing. Sketch the waveforms of collector
voltage, base voltage and magnetizing current. Explain the operation of the oscillator covering one full
cycle, along with necessary equations. Also, mention the advantages and disadvantages of this oscillator.
(13) APR/MAY 17
6. Analyse free running blocking oscillator with base timing using necessary circuit diagram, waveforms and
with advantages and disadvantages. (13) NOV/DEC 16, NOV/DEC 15
7. Define three errors that characterize the performance of time base generators. 6 NOV/DEC 15
8. Explain in detail about monostable blocking oscillator with base timing. 8 APR/MAY 15