# BCT 1305  SEMICONDUCTORS AND DIGITAL LOGIC KCA Past Paper

UNIVERSITY EXAMINATIONS: 2014/2015
ORDINARY EXAMINATION FOR THE BACHELOR OF SCIENCE
IN INFORMATION COMMUNICATION TECHNOLOGY
BCT 1305 SEMICONDUCTORS AND DIGITAL LOGIC
DATE: APRIL, 2015 TIME: 2 HOURS
INSTRUCTIONS: Answer Question ONE and any other TWO

QUESTION ONE
a) Use neat diagrams to show the difference between digital signals and analogue
signals [4 marks]
b) List four advantages of digital systems [4 marks]
c) Use circuit symbols to represent OR and XNOR logic gates [4 marks]
d) Explain the operation of the NAND logic gate. Include the circuit diagram and truth
table [4 marks]
e) Using atomic theory briefly explain the doping process [6 marks]
f) Complete the table below [6 marks]

g) Use two’s complement to solve the problem below
10001(2) – 101 (2) [2 marks]
QUESTION TWO
a) Define the term combinational logic [3 marks]
b) Explain the DeMorgans principle [2 marks]
i) Draw the truth table showing the three inputs and two outputs. [5 marks]
ii) Minimise the resulting expressions using Boolean algebra. [5 marks]
iii) Draw the logic circuit [5 marks]
QUESTION THREE
a) Give the difference between SOP and POS [4 marks]
b) Minimise the following using the K-map to generate the minimum SOP
i) F(ABCD)=(1,2,3,4,,8,9,12,13,14,15) [4 marks]
ii) F(ABCD)=(1,3,6,8) d(2,5,7,12,13,14,15) [4 marks]
iii) F(ABCD)=(2,3,5,6,9) d(10,11,12,13,14,15) [4 marks]
c) Show the implementation of the circuit in Q3 b)i above [4 marks]
QUESTION FOUR
a) Explain the operation of sequential circuits [4 marks]
b) Show the truth table and symbols for XOR and NAND gates [4 marks]
c) Show the circuit and operation of a D flip flop [8 marks]
d) Give two applications of sequential circuits [4 marks]
QUESTION FIVE
a) List two common semiconductor materials [2 marks]
b) Explain the terms forward biasing and reverse biasing. Use suitable diagrams
[8 marks]
c) Using a voltage diagram explain the signal levels that generate logic levels [5 marks]
d) With the aid of suitable diagrams discuss n-type doping [5 marks]

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