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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: A digital circuit that performs the inverse operation of a decoder. A combinational circuit that receives binary information from one of 2n input lines and directs it to a single output line. A combinational circuit that performs the arithmetic addition of two bits. A code that can support only one bit change. 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: Hamming code can be used to detect & correct multiple bit parity errors. DRAM is faster than SRAM. Packing density of CMOS logic is higher to bipolar logic. 555 timer is a digital device. Wire ANDing is possible with TTL devices. 10 ( b ) Explain the functioning of Mod-8 ripple counter. 5

 Q5 ( a ) Differentiate between: PAL and PLA devices. EPROM and EAROM. NMOS and PMOS logic families. Astable and Monostable multivibrators. 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