# VTU Previous Year Question Papers EC 3rd Semester

# Logic design July 2008

**Note : Answer any FIVE full questions, choosing at least two from each part.**

**PART-A**

1 a. What are universal gates? Implement the following function using universal gates only ((A + B)c)d

b. Simplify the following using K – map F(A, B, C, D) ~ ABC + AD + BD + CD + AC + a5 .

c. What are the drawbacks of k-map? Simplify the following expression using Quine – Me Clusky Method. F(A, B, C, D) = S(l,2,8,9,l 0,12,13,14).

2 a. Show that using a 3 – to – 8 decoder and multi -input OR gate. The following Boolean expressions can be realized. F_{1}(A,B,C) = £m(0,4,6), F_{2}(A,B,C)= £111(0,5), F_{3},(A,B,C)= Em(l,2,3,7).

b. Design Decimal – to – BCD encoder?

c. What are the different types of PLD’s and implement the 7 – segment decoder using PLA?

d. Write a verilog code for 4 : 1 multiplexer using case statement.

3 a. i) Perform 8 – bit addition of the decimal numbers – 28 and + 15 in 2’s complement.

ii) Perform 8 – bit subtraction of the decimal numbers – 28 and + 65 in 2’s complement.

b. i) Find the binary addition of (7510)io and (538)io using 16 – bit numbers

ii) Find the binary subtraction of (2QO)io and (125)io using 8 – bit numbers.

c. Explain the binary Adder – subtracted circuit with an example.

4 a. What is Schmitt trigger? Explain Schmitt trigger transfer characteristic.

b. Explain the different types of flip fops along with their truth table. Also explain the race-around condition in a flip flop,

c. Differentiate between combinational circuit and sequential circuit.

**PART-B**

5 a. Explain a 4 -bit serial input shift registers in detail and give its timing diagram.

b. Design a mod – 5 synchronous up counter using JK flip flop.

6 a. Explain Moore model with state synthesis table and also obtain the circuit diagram for Moore model.

b. Design an asynchronous sequential logic circuit for state transition diagram shown in Fig.

Q 6(b).

7 a. What is a binary ladder? Explain the binary ladder with a digital input of 1000.

b. Explain a 2 – bit simultaneous A/D converter.

8 a. With a circuit diagram, explain the operation of the CMOS NAND gate.

b. Explain a 2 – input NAND gate TTL with Totem – pole output with a neat