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End-Term Examination

Fourth Semester [B.Tech] - May 2005

Paper Code : ETEC – 206 Subject : Digital Circuits and Systems

Time : 3 Hours

Maximum Marks : 75

Note : Attempt any 5 questions in all.

Q1

( a )

Simplify the following Boolean function:

z = ( (A+B)' + B' )'

5

( b )

 Explain DeMorgan's laws.

5

( c )

Show the logic diagram of boolean function of Q.1 a using NAND gates.

5

Q2

( a )

Give one word answer to the following:

  1. A digital circuit that performs the inverse operation of a decoder.
  2. A combinational circuit that receives binary information from one of 2n input lines and directs it to a single output line.
  3. A combinational circuit that performs the arithmetic addition of two bits.
  4. A code that can support only one bit change.
  5. A sequential circuit that suffers from race around condition.

5

( b )

 Design a 2 to 4 decoder using NAND gates.

5

( c )

 Compare digital signals with Analog signals, clearly stating their merits and demerits.

5

Q3

( a )

 What is the simplified boolean equation for the Karnaugh map of the figure given below:
     VX YZ      00 01 11 10
00     1  
01        
11   1 1 1
10 1 1 1 1

5

( b )

 Draw the equivalent logic circuit of the simplified equation.

5

( c )

 Implement a 4 to 16 decoder using ROM.

5

Q4

( a )

Justify the following statements:

  1. Hamming code can be used to detect & correct multiple bit parity errors.
  2. DRAM is faster than SRAM.
  3. Packing density of CMOS logic is higher to bipolar logic.
  4. 555 timer is a digital device.
  5. Wire ANDing is possible with TTL devices.

10

( b )

 Explain the functioning of Mod-8 ripple counter.

5

Q5

( a )

 Differentiate between:
  1. PAL and PLA devices.
  2. EPROM and EAROM.
  3. NMOS and PMOS logic families.
  4. Astable and Monostable multivibrators.
  5. Synchronous and Asynchronous counters.

5x3

Q6

( a )

Find the dual of hte followin gexpressions
( x y' + y z + x y' z) x y z

3

( b )

 What is the cannonical form of logic expression? Explain minterms and maxterms.

4

( c )

 What is a mod-5 counter. How it is designed. How a decade counter can be realized using mod-5 counter.

8

Q7

( a )

 Explain the function of a multiplexer. Give an example of multiplexer IC.

5

( b )

 What is the difference betweeen n-bit register and n-bit latch.

4

( c )

 What is a flip-flop. Explain how an S-R flip flopis realized by employing:
(i) NOR gates    (ii) NOR gates

6

Q7

Write short notes on any three of the following:

5 x 3

( a )

 Memory organization

( b )

 Content Addressable Memory

( c )

 Code convertors

( d )

 Comparators

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