ece 1231 sem 1 04/05
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INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIAEND OF SEMESTER EXAMINATION
SEMESTER I, 2004/2005 SESSIONKULLIYY H OF ENGINEERING
Programme : ENGINEERING Level of Study : UG 1
Time : 3:00 pm - 06:00 pm Date : 08/10/2004
Duration : 3 Hrs
Course Code : ECE 1312 Section(s) : 4
Course Title : Electronics
This Question Paper Consists of Six (6)Printed Pages (Including Cover Page) With
Five (5)Questions.
INSTRUCTION(S) TO CANDIDATESDO NOT OPEN UNTIL YOU ARE ASKED TO DO SO
! Total marks of this examination is 100.! This examination is worth 40%of the total assessment.
! Answer all 5 (Five)questions.
Any form of cheating or attempt to cheat is a serious offencewhich may lead to dismissal
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+
vo
+
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vi
2.2 k!2.2 k!2.2 k!
Ideal
diodes
1
2
Q.1 [20 marks]
(a) Sketch the output vo and determine the dc level of the output for the network
shown in Fig. 1(a). Assume that vi= 100 sin(!t). (10 marks)
Fig. 1(a)
(b) What are the maximum and minimum values of Vi, to operate a Zener diode of VZ
= 20 V and IZ (max)= 60 mA. See Fig. 1(b). (10 marks)
220 !
VZ= 20 V 1.2 k!IZM= 60 mA
Fig. 1(b)
vi vo
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+
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Electronics ECE 1312
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Q.2 [20 marks]
(a) Find the values of IBQ, ICQ, VCEQand sketch the dc load line for the circuit shown in
Fig. 2. Assume that #= 100, VBE= 0.7V and ICOhas negligible effect on IC.
(10 marks)
Fig. 2
(b) Compute the voltage gain Av, input impedance Zi, current gain Ai, power gain G,and output impedance Zo for the amplifier shown in Fig. 2. (Assume, r"= 631 !
and the transistor is operating in the active region) (10 marks)
2 k!
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+15 V
500 !
C1
1 k!
1 k!
10 k!
5 k!
C2
C3
RS
R1
R2
RC
RE
RL
+
vin
+
vo
vs
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Q.3 [20 marks]
(a) The MOSFET in Fig. 3has Vto= 1 V, K = 0.25 mA/V2, #= 0. Determine the Q-
point values (VGSQ, IDQand VDSQ) of the given circuit. (10 marks)
Fig. 3
(b) Find the input impedance Zi, output impedance Zo and voltage gain Av for theamplifier in Fig. 3. (Assume gm= 1.77 mS and rd= $!) (10 marks)
100 !
C1
4.7 k!
2.7 k!
3 M!
1 M!
C2
C3
R
R1
R2
RD
RS
RL
+
vin
+
vo
vs 10 k!
+20 V
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Q.4 [20 marks]
(a) Derive an expression for feedback gain GFbased on the amplifier shown in Fig. 4.
(10 marks)
Fig. 4
(b) Calculate GFin each of the following cases and comment on the results.
(10 marks)
G H
1. 500 0.2
2. 5000 -0.01
3. 10 0.08
4. 100 0.01
5. 1000 -0.05
VS V1
VF
VoG
H
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Q.5 [20 marks]
(a) Draw the small signal mid-frequency ac equivalent circuit for the amplifier with
feedback bias shown in Fig. 5. Use Miller theorem to give the expressions for Riand Ro. (10 marks)
Fig. 5
(b) Write True/False (Wrong answer bears negative mark): (10 marks)
1. When the anode is more positive than the cathode of a diode, the condition is
called reverse bias.
2. A semiconductor material has a negative temperature coefficient of resistancewhich means that as temperature increases, the resistance increases.
3. A p-type semiconductor has more valence-band holes than valence band
electrons.
4. A forward bias causes a large depletion region in a p-n junction offers a largeresistance and therefore only permits a small current.
5. Leakage or reverse current is the extremely small current passes through the p-n
junction due to minority carriers.
6. Covalent bond is electrons shared by two neighboring atoms, which form a
recombined electron-hole pair.
7. Conduction band is an energy band in which electrons can move freely within amaterial.
8. When an electron goes from the valence band to the conduction band, it generates
an electron-hole pair.
9. In n-type semiconductor, the electrons are called minority carriers and the Fermi
level lies above the middle of the band gap.
10. At a p-n junction theres an attractive force between the electrons of the n-type
material and the holes of the p-type material.
+VCC
vs
RS C1
RF
C2
RL
vin
vo
+
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