Electronics ECE 1312

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

END OF SEMESTER EXAMINATIONSEMESTER 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

Course Code : ECE 1312 Section(s) : 1 - 9

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

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,I L=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 V γ = 0.65 V and r f=10 Ω. (Hint: determine the transformer turns ratio). (6 marks)

Fig. 1(b).

(c) Repeat question Q.1 (b) using the ideal diode model (Vγ = 0 V and r f=0 Ω). (3 marks)

(d) Derive the output voltage v0for the input voltage vi=V M sin (ωt ) of the ideal diode clamper circuit is as shown in Fig. 1(d). (3 marks)

Fig. 1(d)

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Electronics 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 V CC , RC and RB. Assume that V BE (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 β = 120. (6 marks)

RB

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Electronics ECE 1312

Fig. 2(b)(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 β = 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. Determine the DC collector current. (4 marks)

ii. Prove that the circuit is biased in forward-active mode. (2 marks)iii. Draw the small-signal equivalent circuit. (2 marks)iv. Find the input resistance Riand voltage gain A v=v0/ vs. (6 marks)

Assume that the transistor parameters are; β = 110, VBE (on) = 0.7 V and VA = ∞.

Fig. 3 (b)

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Electronics ECE 1312

(c) A common-emitter circuit is shown in Fig. 3(c), the transistor parameters are, β = 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. Calculate the small-signal transistor parameters, rπ and gm. (2 marks)ii. Draw the small-signal equivalent circuit. (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, V TN=1.8 V , K n=0.15 mA /V 2, gm=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, A v=v0/ v i (4 marks)

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Electronics ECE 1312

Fig. 4(a)

(b)

i. Design the common drain amplifier circuit as shown in Fig. 4(b) for voltage gainAv=v0 / v i=0.925. The parameters of the MOSFET are, gm = 4 mA/V andro = 50 k. (4 marks)

ii. Draw the small signal equivalent circuit (2 marks)

iii. Determine the effect of voltage gain if RS = (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 I DQ=0.6 mA and V DSQ=3.5 V. Given that the transistor parameters are

Kn' =120μA/V2, ( W

L ) = 8 andV TN = 1.5 V (8 marks )

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Electronics ECE 1312

Fig. 5(b)

(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=¿ V. Assume that the input signals are, v I 1=−1.0 V and vI 2=0.5 cos ωt V. (6 marks)

Fig. 5(d)

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Electronics ECE 1312

Some Useful Equations

For pn-junction diode:

For BJT:

For NMOSFET:

K n=Kn

'

2∙ W

L

8

I D=I s(e

v D

V T −1)

gm=I CQ

V T

r π=β V T

I CQ

ro=V A

I CQ

I D=Kn [2 (V GS−V TN ) V DS−VDS2 ]

I D=Kn (V GS−V TN )2

ro=1

I DQ λ

gm=2√ Kn I DQ

Kn=Wμn Cox

2 L

Electronics ECE 1312

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