Questions - International Islamic University Malaysia

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Electronics
ECE 1312
INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA
END OF SEMESTER EXAMINATION
SEMESTER I, 2014/2015 SESSION
KULLIYYAH OF ENGINEERING
Programme
: ENGINEERING
Level of Study
: UG 1
Time
: 2:30 pm - 5:30 pm
Date
: 05/01/2015
Duration
: 3 Hours
Section(s)
:1-9
Course Code : ECE 1312
Course Title
: Electronics
This question paper consists of eight (8) printed pages (including cover page) with five (5)
questions.
INSTRUCTION(S) TO CANDIDATES
DO NOT OPEN UNTIL YOU ARE ASKED TO DO SO
ο‚·
ο‚·
ο‚·
Total mark of this examination is 100.
This examination is worth 50% of the total assessment.
Answer ALL FIVE questions.
Any form of cheating or attempt to cheat is a serious offence which
may lead to dismissal.
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Electronics
ECE 1312
Q.1 [20 marks]
(a) State two characteristics for each conventional pn-junction diode and Ziner diode.
( 4 marks)
(b) Design a full-wave center-tapping rectifier circuit for a desired peak output current,
𝐼𝐿 = 125 mA with a transformer feed as shown in Fig. 1(b). Assume that the transformer primary
is connected with a 220 V(rms) main supply line and the circuit diode cut-in voltage VΞ³ = 0.65 V
and π‘Ÿπ‘“ = 10 Ξ©. (Hint: determine the transformer turns ratio).
(6 marks)
Fig. 1(b).
(c) Repeat question Q.1 (b) using the ideal diode model (VΞ³ = 0 V and π‘Ÿπ‘“ = 0 Ξ©).
(3 marks)
(d) Derive the output voltage 𝑣0 for the input voltage 𝑣i = 𝑉M sin(Ο‰t) of the ideal diode clamper
circuit is as shown in Fig. 1(d).
(3 marks)
Fig. 1(d)
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ECE 1312
(e) Sketch the output voltage waveform for the circuit in Fig. 1 (d) by analyzing the circuit for the
input triangular voltage waveform as shown in Fig. 1(e).
(4 marks)
Fig. 1(e).
Q.2 [20 marks]
(a) A common emitter BJT circuit is designed as shown in Fig. 2(a). The output load line and
defined Q-point of the circuit is shown in Fig. 2(a). Determine the required values of 𝑉CC , 𝑅C
and 𝑅B . Assume that 𝑉BE (on) = 0.7 V.
(6 marks)
Fig. 2(a)
(b) The voltage transfer characteristic and its BJT circuit are shown in Fig. 2(b). Find the value of the
resistor, RB by assuming VI = 1.9 V. Given the valus of VBE(on) = 0.7 V and Ξ² = 120.
RB
Fig. 2(b)
3
(6 marks)
Electronics
ECE 1312
(c) What is the purpose of biasing?
(2 marks)
(d) For the biasing circuit shown in Fig. 2(d), RB = 250 k, RC = 5 k and VCC = 10 V. By assuming
that VBE(on) = 0.7 V and Ξ² = 30, calculate IBQ, ICQ, and VCEQ.
(6 marks)
Fig. 2(d)
Q. 3 [20 marks]
(a) Give two differences between common emitter and common collector amplifier circuits.
(2 marks)
(b) A common collector circuit is shown in Fig. 3 (b),
i.
ii.
iii.
iv.
Determine the DC collector current.
Prove that the circuit is biased in forward-active mode.
Draw the small-signal equivalent circuit.
Find the input resistance 𝑅𝑖 and voltage gain 𝐴𝑣 = 𝑣0 /𝑣𝑠 .
Assume that the transistor parameters are; β = 110, VBE (on) = 0.7 V and VA = ∞.
Fig. 3 (b)
4
(4 marks)
(2 marks)
(2 marks)
(6 marks)
Electronics
ECE 1312
(c) A common-emitter circuit is shown in Fig. 3(c), the transistor parameters are, Ξ² = 110,
VBE(on) = 0.65 V, ICQ = 0.2 mA and VCEQ = 3.2 V. Assume that, RS = 1 kΩ, RE = 2.5 kΩ,
RC = 13 kΩ and ro = ∞.
i.
ii.
Calculate the small-signal transistor parameters, rΟ€ and gm.
Draw the small-signal equivalent circuit.
(2 marks)
(2 marks)
Fig. 3(c)
Q.4 [20 marks]
(a) A common source amplifier is designed as shown in Fig. 4(a). Consider the MOSFET parameters
are, 𝑉𝑇𝑁 = 1.8 V, 𝐾𝑛 = 0.15 mA/V 2, π‘”π‘š = 0.77 mA/V and  = 0.
i.
Verify that the MOSFET is working in the saturation region. Assuming that VGS = VDS.
(3 marks)
ii. Draw the small signal equivalent circuit.
(3 marks)
iii. Determine the value of the voltage gain, 𝐴𝑣 = 𝑣0 /𝑣𝑖
(4 marks)
Fig. 4(a)
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Electronics
ECE 1312
(b)
i.
Design the common drain amplifier circuit as shown in Fig. 4(b) for voltage gain
Av = v0 ⁄vi = 0.925. The parameters of the MOSFET are, gm = 4 mA/V and
ro = 50 k.
(4 marks)
ii.
Draw the small signal equivalent circuit
(2 marks)
iii. Determine the effect of voltage gain if RS = ο‚₯
(4 marks)
Fig. 4(b)
Q. 5 [20 marks]
(a) Compare four differences between BJT and MOSFET.
(4 marks )
(b) Design an n-channel MOSFET circuit shown in Fig. 5(b) to fulfill a set of conditions
as 𝐼𝐷𝑄 = 0.6 mA and 𝑉𝐷𝑆𝑄 = 3.5 V. Given that the transistor parameters are
𝐾𝑛′ = 120 ΞΌA/V2, (π‘Šβ„πΏ) = 8 and 𝑉𝑇𝑁 = 1.5 V
(8 marks )
Fig. 5(b)
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Electronics
ECE 1312
(c) Design the non-inverting amplifier as shown in Fig. 5(c) with a voltage gain of 25 by
determining the value of resistance 𝑅1 .
(2 marks)
Fig. 5(c)
(d) A summing amplifier is shown in Fig. 5(d) with a feedback resistance, RF = 10 kΩ. Design
the circuit to produce a specific output signal, such that 𝑣0 = (1.25 βˆ’ 2.5 cos πœ”π‘‘) V. Assume
that the input signals are, 𝑣𝐼1 = βˆ’1.0 V and 𝑣𝐼2 = 0.5 cos πœ”π‘‘ V.
(6 marks)
Fig. 5(d)
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Electronics
ECE 1312
Some Useful Equations
For pn-junction diode:
I D ο€½ I s (e
vD
VT
ο€­ 1)
For BJT:
I CQ
gm ο€½
r ο€½
ro ο€½
VT
 VT
I CQ
VA
I CQ
For NMOSFET:
I D ο€½ Kn [2 VGS ο€­ VTN  VDS ο€­ VDS ]
2
I D ο€½ K n VGS ο€­ VTN 
2
ro ο€½
1
I DQ 
g m ο€½ 2 K n I DQ
Kn ο€½
W n Cox
2L
𝐾𝑛′ π‘Š
𝐾𝑛 =
βˆ™
2 𝐿
8
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