# VTU Previous Exam papers BE CS 3rd Semester

# Logic Design May/June 2010

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

**PART-A**

1 a. Simplify the given Boolean function by using K-map method and express it in SOP form. Realise logic circuit by using NAND gates only. f(A,B,C, D) = (m(7, 9, 10, 11, 12, 13, 14, 15))

b. Simplify following Boolean function by using K-map method in POS form: f (A, B, C, D) = ^{m}(0,1,2,3,4,5,7)

c. Find prime implicants for the Boolean expression by using Quine McClusky method, f (A, B, C, D) = ]T (1,3,6,7,8,9,10,12,14,15) + d(l 1,13)

2 a. Define decoder. Draw logic diagram of 3:8 decoder with enable input.

b. Implement the given Boolean function by using 8:1 multiplexer. f(A,B,C,D) = ]T(0,l, 3,5,7,11,12,13,14)

c. With a neat diagram, explain the decimal to BCD encoder.

3 a.What are the three different models for writing a module body in verilog HDL? Give example for any one model.

b. With truth table and a neat logic diagram, explain full adder implementation.

c. Explain how IG 7483 can be used as 4 bit adder/subtractor.

4 a. With transfer characteristic, explain how Schmitt trigger converts a random waveform into a rectangular waveform.

b. Explain basic S.R flip-flop by using NOR gate. What is the drawback of S~R flip-flop? How J-K flip-flop is obtained from S-R flip-flop?

c. Find out characteristic equations of J-K flip-flop and D flip-flop.

**PART-B**

5 a. Explain any two types of shift register with waveforms. How Johnson counter is obtained from shift register?

b. Design Mod-6 synchronous counter by using J-K flip-flop. Give excitation table of J-K flip-flop, state diagram and state transition table.

6 a. Differentiate between Moore and Mealy model of synchronous sequential

circuit.

b. Reduce the state transition diagram of Mealy model by row elimination method and implication table method. State transition diagram. r

Fig. Q6 (b)

7 a. Explain with neat diagram, R-2R ladder type 4 bit D to A converter. Find out analog output if input is 1100 and T- +5 volts. For 10 bit DAC if full scale output is 10.24 volts, what is resolution? (10 Marks)

b. Explain with a neat diagram, successive approximation type DAC.

8 a. With a neat circuit diagram, explain the operation of a two input TTL NAND gate with tolem pole output.

b. Explain with a neat diagram, CMOS inverter.

c. Explain CMOS characteristics.