Original filename: analog.pdf
Title: EXAMINATION PAPER
Author: Staff Use
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Health, Engineering and
Engineering and Science
(PLEASE LIST ALL CODES AND TITLES
PLEASE MARK THE CAMPUS/S
WHERE EXAM WILL BE SAT
Systems and Applications 2D
FOR WHICH THIS PAPER IS TO BE USED)
DURATION OF EXAMINATION
THIS EXAMINATION COUNTS FOR
+ 15 MINUTES READING TIME
OF THE ASSESSMENT IN THIS SUBJECT.
EXAMINATION PAPERS DETAILS
TOTAL NUMBER OF PAGES (including this one)
NUMBER OF QUESTIONS
NUMBER OF QUESTIONS TO BE ATTEMPTED
SPECIAL INSTRUCTIONS TO CANDIDATES
Use a separate answer booklet for each
EXAMINATION MATERIAL PERMITTED TO BE USED BY CANDIDATES :
Section A: Analogue Electronics, Text Book “Microelectronic Circuits”, Sedra & Smith.
Section B: Digital Electronics, Two A4 pages (sides) of written material.
Section C: Energy Conversion, Two A4 pages (sides) of written material.
EXAMINATION MATERIAL SUPPLIED BY STUDENT ADMINISTRATION
COMPUTER MULTIPLE CHOICE ANSWER SHEET
CAN THE EXAM PAPER BE RELEASED TO STUDENTS
CAN THE EXAM PAPER BE RELEASED TO LIBRARY
(Examiner/s must be available on this number for duration of this examination)
VEF2004 Systems and Applications 2D (Section A, B & C)
IMPORTANT INSTRUCTIONS TO STUDENTS
SECTION A IS THE ANALOGUE ELECTRONCS SECTION
SECTION B IS THE DIGITAL ELECTRONICS SECTION
SECTION C IS THE ENERGY CONVERSION SECTION
Please use a separate answer booklet for each section.
SECTION A: Analogue Electronics
Question A1. (Frequency Response) (20 Marks)
An MOSFET common-source amplifier
has Rin = 2 MΩ, gm = 4 mA/V, ro = 100 kΩ,
RD = 10 kΩ, Cgs = 2 pF. And Cgd = 0.5 pF. The amplifier is fed from a voltage source with
internal resistance of 500 kΩ and is connected to a 10-kΩ load.
a) Draw the circuit and label all components
b) Find the overall mid-band gain AM
c) Find the upper 3-dB frequency fH.
d) If we want to double fH what is the most appropriate components to be change.
Question A2 (Differential Amplifier) (20 Marks)
Figure-1 is a BJT differential amplifier using transistors with = 100 and VA = 100 V.
a) Find the differential gain and the differential input resistance
b) Find the common-mode gain
Question A3 (Amplifier stability) (20 Marks)
An op amp designed to have a low-frequency gain of 105 and high-frequency response
dominated by a single pole at ω = 100 rad/s, acquires, through a manufacturing error, a pair of
additional poles at ω = 10,000 rad/s.
a) At what frequency does the total phase shift reach 180o?
b) At this frequency, for what value of β, assumed to be frequency independent?
SECTION B: Digital Electronics
Please see the separate pdf file for the Digital part of the exam.
SECTION C: Energy Conversion
Question 1 (10 marks)
Consider the magnetic structure shown in Figure 1. Find the current in the 50-turn winding to
set up a flux density of 0.8T in the structure, assuming that the relative permeability of the
core material is 2000. Use the concept of reluctance in your solution.
Figure 1: Magnetic structure for Question 1.
Question 2 (20+10=30 marks)
A 15kVA 2300V/230V transformer is to be tested to determine its excitation branch
components, its series impedances, and its voltage regulation. The following data have been
taken from the primary side of the transformer:
a) Find the equivalent circuit of this transformer referred to the high voltage side (primary)
and draw the equivalent circuit diagram;
b) Determine the efficiency of the transformer at full load with a lagging power factor of 0.8.
Question 3 (20 marks).
a) How many methods can be used for speed control of a DC motor?
b) The armature resistance of a 220 V shunt motor is 2. At no load, the line current is 2.4 A
at rated voltage. The field current is 0.8 A, and the speed is 1440 rpm. Find the motor
speed when the line current increases to 12.8 A, the field current remaining the same.
Assume that armature reaction does not affect the field flux.
c) The counter emf of a shunt motor is 227V, the field resistance is 160, and the field
current is 1.5A. The line current is 36.5 A. Find the armature resistance. If the line current
during starting must be limited to 60A, how much starter resistance must be added in
series with the armature?
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