VTU Previous Exam Papers BE CS 3rd Semester Logic Design December 2010

VTU Previous Exam papers BE CS 3rd Semester

Logic Design December 2010


Note: Answer any FIVE full questions, selecting at least TWO questions from each part.


1. Draw the logic circuit whose Boolean equation is Y = A + B + C , use only NAND gates.

b. Find the minimal sum and minimal product using Karnaugh map. f(a,b,c,d) = ^m(6,7,9,10,13) + d(l,4,5,ll)

c. Find the prime implicants for the following function using Quine Mccluskey      method: f(a,b,c, d) = m(l,2,8,9,l 0,12,13,14)


2 a. Implement the following function using a 8 : 1 multiplexer


b. Describe the working principle of a 3 : 8 decoder. Realize the following Boolean expressions using the 3 : 8 decoder : F, (A, B, C) = £ m(l,2,3,4) F2 (A, B, C) = £ m(3,5,7)           (06 Marks)

c. What is PLA? How does PLA differ from PAL?

d. Write HDL code for a 4 to 1 Mux considering any model.


3 a. How is 2’s complement representation used to perform subtraction? Give an example.

b. Show how two 7483 can be used to add/subtract two 8 bit numbers. Draw a neat diagram and explain its working.

c.   Design a 2 bit fast adder. Give its implementation using gates.


4 a. Calculate the clock cycle time for a system that uses a clock, that has a frequency of:

i)10 MHz                   ii) 6 MHz                  iii) 750 KHz

b. With a neat block diagram, explain the working of a Master-Slave JK flip flop. Also write its truth table.                                                                                                                                (07‘Marks)

c.   Explain the function of the circuit shown here with the state transition diagram.



5 a. Draw the logic diagram of a 4 bit serial in serial out shift register using JK flip flop and explain its working with an example.

b. Give the HDL code for a shift register of 5 bits constructed using D flip flops.

c. Construct a mod 8 asynchronous counter and write the truth table and draw waveforms.

d. Design a mod 4 synchronous counter using a -ve edge triggered JK flip flop. Draw the state transition diagram.                                                                                                      (06 Marks)


6 a. For the following state transition diagram, design equations for Moore model and generate the circuit diagram.


Fig.Q6 (a)

b. Design an asynchronous sequential logic circuit for state transition diagram shown below: tot\


30\ I o 1)

       Fig.Q6 (b)

c.   How does state transition diagram of a Moore machine differ from Mealy machine?

7 a. Draw a binary ladder network for a digital input 1000 and obtain its equivalent circuit.

b.   Explain the concept of “successive approximation” of a A/D converter.

c. In a 8 bit counter type A/D converter driven by 500 KHz clock, find :

i) Conversion time

ii) Average conversion time

iii) Maximum conversion time.


8 a. Explain the working of CMOS NAND, NOR gates.

b. Explain with a neat diagram, working of a 2 input NAND gate TTL with

totempole output.

c. Explain how transistor acts as a switch. Define power dissipation and propagation delay time.


Leave a Comment