H.T.No.
Code No: EC2529 GEC-R17
II B.Tech II Semester Supplementary Examinations, April 2021
ANALOG CIRCUITS
(Electronics and Communication Engineering)
Time: 3 Hours Max. Marks: 60
Note: Answer one question from each unit.
All questions carry equal marks.
6 × 10 = 60M
UNIT-I
1. Analyze the CS amplifier with source degeneration resistance to find the expressions for Rin,
Rout, Av and Gv. (10M)
(OR)
2. In the circuit shown in figure, vsig is a small sine wave signal with zero average. The transistor
β is 100. (i) Find the value of RE to establish a dc emitter current of about 0.5 mA, (ii) Find RC
to establish a dc collector voltage of about +5V, (iii) draw the small-signal equivalent circuit
of the amplifier and determine its overall voltage gain for R L= 10 kΩ and the transistor
r0 = 200 kΩ. (10M)
UNIT-II
3. Derive the expression for common emitter short-circuit current gain. (10M)
(OR)
4. Sketch the frequency response characteristics of MOS cascode configuration and derive the
expression for bandwidth. (10M)
UNIT-III
5. Explain the large-signal operation of MOS differential pair and derive the expressions for
instantaneous drain currents. (10M)
(OR)
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6. a) What causes the common-mode gain in MOS differential amplifiers? (4M)
b) A BJT current mirror is having matched transistors with β= 100. If IREF = 3 mA, find (i)
the output current Io and (ii) the current transfer ratio. (6M)
UNIT-IV
7. a) Find (i) the closed-loop gain and (ii) effect of finite open-loop gain when the op-amp is
under the non-inverting configuration. (7M)
b) Draw the circuit of an op-amp weighted summer. (3M)
(OR)
8. Derive the expressions for centre frequency and quality factor of a tuned amplifier. (10M)
UNIT-V
9. a) Use the appropriate topology to provide a negative feedback to current amplifier and
derive the expressions for input resistance, output resistance, and current gain. (6M)
b) A negative-feedback amplifier has a closed-loop gain Af = 100 and an open-loop gain
A = 104. What is the feedback factor β? If a manufacturing error results in a reduction of A
to103, what closed-loop gain results? What is the percentage change in Af corresponding
to this factor of 10 reduction in A? (4M)
(OR)
10. For the circuit shown in figure, break the loop at node X and find the loop gain. For R = 10
kΩ, find C and Rf to obtain sinusoidal oscillations at 10 kHz. (10M)
UNIT-VI
11. a) Define power conversion efficiency. (2M)
b) For the Class A output stage, VCC=20 V, VCEsat =0.2 V, VBE=0.7 V and constant, and β is
very high. Find (i) the value of R that will establish a bias current sufficiently large to
allow the largest possible output signal swing for RL=5 kΩ and (ii) determine the resulting
output signal swing. (8M)
(OR)
12. a) Explain the need of heat sink in a power amplifier. (4M)
b) A power transistor is specified to have a maximum junction temperature of 130°C. When
the device is operated at this junction temperature with a heat sink, the case temperature is
found to be 90°C. The case is attached to the heat sink with a bond having a thermal
resistance θCS = 0.5°C/W and the thermal resistance of the heat sink θSA = 0.l°C/W. If the
ambient temperature is 30°C what is the power being dissipated in the device? What is the
thermal resistance of the device, θJC from junction to case? (6M)
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