GITAM University 2006 B.E Electronics & Tele-Communication Engineering DIGITAL ELECTRONICS - Question Paper

College of Engineering
Gandhi Institute of Technology and Management, Visakhapatnam
(Affiliated to Andhra University)

B.E.(Electronics and Communications Engineering)
Second Year 2nd Semester exams 2005-2006
(Autonomous Stream)

EC 221: Digital Circuits and Systems

Time: three Hours Max. Marks: 60


1. Answer ques. No. one ( Part – A) and any 4 of the remaining 7 (Part – B)
2. All parts of a ques. must be answered in 1 place, otherwise they will not be valued.
3. Figures in the right hand margin indicate marks allotted.

PART – A

1. Answer the subsequent in 1 or 2 phrases each (10x2=20)

a) Determine the base of the numbers in every case for the subsequent operations to be accurate.
i) 62/5 = 12 ii) 24+17 = 40
b) Simplify the subsequent Boolean expressions to a minimum number of literals.


c) Realize a 3 input NOR gate using 2 input NOR gates only.
d) Realize the full adder circuit using half adder circuits and logic gate.
e) Specify the size of a ROM that will accommodate the truth table for a BCD – to seven-segment decoder with an enable input.
f) Draw the 4:1 multiplexer realization of a full subtractor.
g) Draw the circuit of CMOS NAND gate.
h) Write the excitation Table of S-R flip-flop.
i) Draw the state diagram of T flip-flop.
j) What is meant by dynamic hazards in Asynchronous sequential circuits?


PART – B


ans any 4 of the subsequent. If you attempt more than 4 questions, only the 1st 4 in order will be valued


2. a) A eight bit data is encoded using Hamming code and is then transmitted. The received bit stream is 000011101010. obtain the fault in the code and accurate it. elaborate the data bits? (5)
b) Express the subsequent function in product of maxterms.
F(u,v,w,x) = v'x+u'x+vx
(5)

3. a) Obtain essential prime implicants for the subsequent function using tabulation method
f (A, B,C,D) = Sm (0,2,3,4,5,7,8,9,13,15) (5)
b) Obtain simplified POS expression for the subsequent function using K-map
f (A, B,C,D) = Sm (0, 1, 2,6, 8,10,11,12) (5)

4. a) Explain carry look ahead adder. (5)
b) Implement a PLA structure for a full adder (5)

5. a) Draw the circuit of DTL NAND gate and discuss. (5)
b) What is Race around problem? discuss methods to avoid it. (5)

6. a) Design Modulus – 13 asynchronous counter with JK – Flip flops. (5)
b) Design a detector to detect the sequence 11011 with overlap. (5)

7. a) A sequential circuit with 2 D flip-flops, DA and DB; 2 inputs x and y; and 1 output z is specified by the subsequent next state and output formula.
D(A[t+1]) = x'y+D(A)
D(B[t+1]) = x'D(B)+D(A)
Z = D(B)
i) Draw the logic diagram of the circuit.
ii) Draw the corresponding state diagram. (6)
b) What are the main differences ranging from synchronous and asynchronous sequential circuits? (4)

8. a) Find a circuit that has no static hazards and implements the Boolean function.
F(u,v,w,x) = S(0,2,6,7,8,10,12) (6)
b) Define fundamental – mode operation. (2)
c) Explain the difference ranging from stable and unstable states. (2)

Earning:   Approval pending.