Download EC6401-EC II -model exam

LOYOLA – ICAM
COLLEGE OF ENGINEERING ANDTECHNOLOGY (LICET)
Loyola Campus, Nungambakkam , Chennai – 34
Branch: ECE
Date: 06-04-2015
Semester: IV
Time: 1.00 – 05.00 pm (3 Hrs)
MODEL EXAM
ELECTRONIC CIRCUITS II (EC6401)
Part-A (Answer all the questions)
(10x2=20)
1. Define sensitivity and Desensitivity of gain in feedback amplifiers.
2. An amplifier has a voltage gain of 1000. With negative feedback, the voltage gain reduces to 10.
Calculate the fraction of the output that is feedback to the input.
3. What are the advantages and disadvantages of RC phase shift oscillators?
4. Crystal oscillators possess high degree of frequency stability – justify
5. Define ‘Q’ of tank circuit.
6. A tuned amplifier has its maximum gain at a frequency of 2 MHz and has a bandwidth of 50 kHz.
Calculate the Q-factor.
7. State the role of commutating capacitors in Bistable multivibrator.
8. Draw a circuit of a RC integrator and mention the condition under which the circuit behaves as a
integrator.
9.
10.1
10.
List the different methods available for generation of Ramp waveforms.
What is a blocking oscillator?
Part-B (Answer all the questions)
(5x16=80)
11.a (i) Draw the circuits of voltage shunt and current series feedback amplifiers and
Derive the expressions for input impedance Rif .
(10)
(ii) Discuss Nyquist criterion for stability of feedback amplifiers, with the help of
Nyquist plot and Bode plot.
(6)
(OR)
b i)what is the effect of negative feedback on the bandwidth and the distortion of a
amplifier.
ii) A negative feedback is used to reduce the noise from the amplifier by 80%. What
must be the % negative feedback to accomplish this, if the amplifier voltage gain is 100?
(10)
12. a. Draw the circuit diagram and explain the working of Twin T oscillator. Also derive
the expression for frequency of oscillation.
(OR)
b. Explain weinbridge oscillator, derive its frequency of oscillation and its gain.
13. a. (i) Draw the circuit diagram and the equivalent circuit of a capacitor-coupled single tuned amplifier
and explain its operation. Derive the equations for voltage gain and for 3-dB bandwidth. Sketch
also the frequency response of the amplifier.
(12)
(ii) A single tuned transistor amplifier is used to amplify modulated RF carrier of 600kHz and
bandwidth of 15 kHz. The circuit has total output resistance Rt = 20 kΩ and output-capacitance
Co = 50 pF. Calculate the values of inductance and capacitance of tuned circuit.
(4)
(OR)
b. Explain i) Class C amplifiers and efficiency of class C tuned amplifier (ii) Narrow
band neutralization
14 a. i) Draw the circuit of the collector coupled transistor astable multivibrator. Explain
the operation and mention the disadvantages of the circuit.
ii) Design an astable multivibrator circuit to generate a 1KHz square wave. The
supply voltage is 5V and the collector current is to be 2mA. Assume hfe=70.
(OR)
b. Calculate the component vales of a monostable multivibrator developing an output
pulse of 140 s duration. Assume hfemin=20, Ic(sat) = 6mA,Vcc=6V, Vbb= -1.5V.
Draw the circuit for monostable multivibrator with calculated values.
15 a. With neat circuit diagram explain the working of a mono stable blocking oscillator using emitter
timing. Draw the equivalent circuit. Also derive the expression for pulse width.
(OR)
b. i) With a neat diagram explain a circuit for generating sweep using UJT. Obtain the
expression for sweep period and frequency.
(10)
ii) In a simple UJT circuit the resistance and capacitance are 100 K ohms and
0.4microfarad. The ratio of peak point voltage to supply voltage is 0.57. find the
frequency of sweep.
(6)