UNIVERSITY EXAMINATIONS: 2020/2021
EXAMINATION FOR THE DEGREES OF BACHELOR OF SCIENCE
IN INFORMATION SECURITY & FORENSICS
BISF 1208: SEMICONDUCTORS AND DIGITAL ELECTRONICS
FULLTIME/ PART TIME/DISTANCE LEARNING
DATE: DECEMBER, 2021 TIME: 2 HOURS
INSTRUCTIONS: Question ONE IS COMPULSORY, Choose TWO OTHER Questions
i. Two ways of ionizing an atom
ii. Two advantages of silicon over germanium diodes
(b) Define the following with respect to semiconductors:
i. Covalent bond
ii. Drift current
(c) With the aid of a labelled diagram, describe the formation of depletion layer at the
(d) Figure 1 shows a diagram of an N- type material of resistance 2 KΩ connected
across a 15V d.c supply.
i. Redraw the diagram showing the direction of electrons and holes inside the
ii. Taking the electronic charge, e=1.6 X 10-19 C, determine the
I. Current through the material
II. Number of electrons passing through a given point per second
N- TYPE MATERIAL
III. Electrical energy expended if the current is maintained for
(e) Draw the circuit of a common collector configuration of a transistor amplifier.
(a) Define the following
i. Transistor biasing
ii. Transistor saturation
iii. Feedback current
(b) Figure 2 shows a circuit diagram of an amplifier using the collector base feedback
Taking β=50 and Vbe=0.7V, determine the:
i. Base current Ib;
ii. Collector current Ic:
iii. Collector emitter voltage, Vce
(c) Sketch the transfer characteristic curve for a common emitter transistor.
(a) State three(3) advantages and disadvantages of FETs.
(b) Using a diagram of a CMOS voltage multiplier circuit:
i. Explain its operation
ii. Sketch the output wave form, when subjected to sinusoidal wave form at the input
iii. State three applications of this circuit
(a) Draw a well labelled diagram of half wave regulated power supply and explain the
function of each component used
(b) A full wave bridge rectifier is supplied from a transformer whose secondary voltage is
i. Peak value of the secondary voltage:
ii. DC voltage of the rectifier output;
iii. Ripple factor.
(a) State three:
i. Components of sinusoidal wave.
ii. Biasing methods of bipolar junction transistor (BJT)
(b) A sinusoidal wave of 50Hz with maximum voltage of 10V for a period of 2nS.
i. Its instantaneous voltage
ii. Time t when frequency shifted to 100Hz
iii. Its instantaneous voltage at t=2µs in (b)ii above