Electronic Final Exam Paper

Topics: Bipolar junction transistor, Diode, P-n junction Pages: 6 (1105 words) Published: April 25, 2013
Programme Time Duration : ENGINEERING : 2:30 pm - 5:30 pm : 3 Hrs Section(s) : 3 Level of Study Date : UG 1 : 24/10/2005

Course Code : ECE 1312 Course Title : Electronics

This Question Paper Consists of Eight (8) Printed Pages (Including Cover Page) With Six (6) Questions. INSTRUCTION(S) TO CANDIDATES


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Total marks of this examination is 100. This examination is worth 40% of the total assessment. This examination consists of two parts. You are required to answer all questions from part A and choose any 3 (three) questions from part B.

Any form of cheating or attempt to cheat is a serious offence which may lead to dismissal.

Electronics Part A (Answer all questions)

ECE 1312

Q.1 [10 marks] 1. A PN junction is forward biased when: a. the applied potential causes the N-type material to be more positive than the P-type material b. the applied potential causes the N-type material to be more negative than the P-type material c. both materials are at the same potential d. all of the above e. none of the above 2. Which of the following circuits is used to change the dc reference of a signal without changing the shape of the signal? a. a clipper b. a clamper c. a voltage multiplier d. a voltage divider e. none of the above 3. The circuit shown in Fig.1. is a : a. series clipper b. shunt clipper c. series clamper d. shunt clamper e. all of above Fig.1. 4. The maximum reverse bias potential that can be applied to a Zener diode before it enters the Zener region is called the: a. threshold voltage b. peak inverse voltage c. barrier voltage d. depletion voltage e. none of the above 5. In the Zener region, the current can increase a lot and the voltage across the diode _________. a. can increase a lot b. is almost constant c. is almost constant d. can increase a lot e. none of the above


Electronics 6. Bipolar junction transistor (BJT) is commonly used as : a. the primary component in amplifiers b. shunt clipper circuits c. the primary component in rectifiers d. series clamper circuits e. all of above 7. When a BJT operates in the cut-off region: a. b. c. d. e. base-emitter junction forward biased reversed biased forward biased reversed biased none of the above and and and and base-collector junction reversed biased forward biased forward biased reversed biased

ECE 1312

7. The emitter stabilized bias circuit shown in Fig.2. uses a silicon transistor, RB = 120kΩ, RC =1 kΩ and RE = 500 Ω and VCC = 15V. The base current is: a. 89.0 mA b. 89.0 µA c. 0.199 mA d. 0.199 µA e. none of the above

Fig.2. 8. The maximum current in a JFET is defined as IDSS and occurs when VGS is equal to ________. a. zero volts b. pinch-off voltage c. a small positive voltage d. greater than pinch-off voltage e. none of the above 10. The Enhancement MOSFET can operates in: a. the depletion mode only b. the enhancement mode only c. the depletion mode and enhancement mode d. none of the above



ECE 1312

Q.2 [10 marks] (a) Draw the transfer characteristic of a p-channel JFET defined by IDSS = 10 mA and VP = 6V, consider at least 4 points. Use the graph paper provided. (4 marks) (b) Sketch a PN junction, showing the charges stored in the depletion region. Also, sketch the hole and electron concentrations against distance across the junction. (4 marks) List two main differences between bipolar junction transistors (BJTs) and field effect transistors (FETs). (2 marks)


Part B [Answer any 3 (THREE) questions.] Q.3 [20 marks] (a) Determine the output voltage of an Op-Amp for input voltages of Vi1=150 µV and Vi2= 140 µV. The CMRR of the amplifier is 100 and the differential gain Ad is 4000. Given 1 Vcm ⎞ ⎛ the relation between CMRR and Vo = AdVd ⎜1 + ⎟. ⎝ CMRR Vd ⎠ (6 marks) (b) Derive the output voltage Vo, for the ideal Op-Amp...
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