# RGPV Exams Questions Papers IV SEM – Digital Circuit & systems – June -2008

B.E. (Fourth semester) EXAMINATION,JUNE, 2008

(Common for EC/EE/EX Engg.)

(DIGITAL CIRCUIT AND SYSTEM)

Note:     Attempt any five questions. All question carry equal marks.

1   (a) Convert the following:

(i) (27.125)10= (  )8=(  )2        (ii) (237)8=(   )10

(iii) (249)10=(  )16= (  )2          (iv) (20.305)­10=(  )BCD

(b)  Prove the following using De Morgen’s  theorem:

(A+B)(C+D) =(A+B)+ (C+D)

And hence that one OR-AND configuration is equivalent to NOR- NOR configuration. Realize  the

logical equation above using  :

(i) OR and gates      (ii) Only NOR gates

2   (a) Minimize the following logic function using K-map and realize using NAND gates:

F1(A,B,C,D)=?m(1,3,5,8,9,11,15)+d(2, 13)

(b) Design a full adder and derive the expressions for output and realize it with NAND gates.

3   (a) Explain the operation of look ahead carry generator.

(b) Explain the working of a 4-bit parallel binary adder.

4.   (a) Explain the working of Schmitt trigger square wave generator .

(b) Explain the operation of the RTI  NOR gate.

5.   (a) Explain a Synchronous 4-bit up-down counter.

(b) What is shift register? How a word is stored in a serial shift resister?

6.  (a) Explain ROM and its working . How is different from PLA.

(b)  Implement the given Boolean function with 8×1 multiplexer:

F(ABCD)=?m(0,3,5,6,8,9,10,12,15)

7   (a) Draw the block diagram of successive approximation A to D converter and explain its operation.

(b) Design BCD to excess-3 code converter circuit and draw the logic diagram.

8     Write short notes on any two of the following :

(i) BCD adder  (ii) Astable multavibrator     (iii) Decoder and encoder   (iv) Sample and hold circuit

(v)  TTL circuits