Digital Electronics July-2011

UNIT – I

1. (a) Find the radix of the given number system.

(i)  (23)x +(12)8 =(1B)16

(ii) (110)x + (15)x = (29)x

(b) List the major advantages of digital electronics over analog electronics.

(c) What is the advantages of using Gray code ? Explain any one area of its application with the help of a block diagram.,

OR

1. (a) Realize the following expressions :

(i)   Y = (abc + bc)c using NOR gates only

(ii) Y = (AB + BC)C using NAND gates only

(b) What is reflective code? With the help of an example explain the difference between reflective and sequential code.

(c) A seven bit hamming code is received as 1101011 is the received code correct? If not then find the correct code which was transmitted.

UNIT – II

2. (a) Why CMOS IC’s are preferred for battery operated function?

(b) Explain the role of diode D in the output circuit of totem – pole output gate. What will happen if it is removed from the circuit?

(c) Compare different parameters of TTL and CMOS logic families.

OR

2 (a) What parameters have to be taken care while driving a CMOS gate by a TTL gate ?

(b) Why ECL family is the fastest logic family? Explain.

(c) Explain the interfacing concept of TTL gate driving a CMOS gate with equal power supply voltage.

UNIT-III

3. (a) Minimize the following equation using K – map. Realize the output equation using NAND gates only.

Y = M 0,M 2,M 4,M 6,M 7

(b) Find the minimal expression using Quine-Mc Cluskey method. f (A,B,C,D) = ]jjT w (1,5,6,12,13,14) + ti(2,4)

(c) Design a digital circuit which accepts inputs between 0 to 9 and generates logic T if the input is an odd number and ‘O’ if the input is even number.

(d) If W(.4,S,C,Z)) w(0,1,2,3,4,6,7,10,11,12,15)   X(A, B,C, m (0,1,2,5,6,9,10,11,12,13,14)

Find Y = W and realize the output equation using NAND gates only.

UNIT – IV

4 (a) Explain in easy steps how a full subtractor can be implemented using 4:1 multiplexers.

(b) Implement 3 – input OR and Ex OR gate using 2 : 1 multiplexers.

OR

4. (a) With the help of neat circuit diagram explain the experimental setup of BCD to seven segment decoder process using 7447 IC. Explain how leading zero’s are eliminated in multi-digit display.

(b) Explain in easy steps how a full adder can be implemented using 1:4 demultiplexers. _

UNIT – V

5. (a) With the help of an excitation table explain how a D – flip – flop can be converted into T flip – flop.

(b) What is a ring counter ? Where it is used ? If in a 4 – bit ring counter due to false triggering an extra bit is initiated in the ring, say 1001. Explain how this extra bit will be eliminated from the ring counter.

OR

5. (a) With the help of an excitation table, explain how a 3 – bit synchronous up counter can be designed using T – flip – flops.

(b) With the help of simple circuit diagram explain the difference in working of asynchronous and synchronous counter.