MULTIPLEXERS - COMBINATIONAL CIRCUITS

1. Implementation of  8x1 MUX using 2x1 MUX

 Needs 7 nos of 2x1 MUX to implement 8x1 MUX.

2. The output the following circuit is

 Input I0 = 0 , I1=1, I2 = 1 ,I3=0

F = Minterms(1,2)

F = P'Q + PQ' = P XOR Q

3. Without any additional circuitry an 8x1 MUX can be used to obtain  All the functions of 3 variables and some but not all the function of 4 variables.

4.The minterms of the following circuit are

F = Minterms (1,3,4,11,12,13,14,15)

5. Find the function implemented in the following circuit.

S = Minterm (1,2,4,7)
C = Minterm (3,5,6,7)

The  function implements Full Adder

6. The below diagram implement two bit by two bit binary multiplier

 7. A 4 variable logic circuit can be designed using 

• a 16x1 MUX
• a 8x1 MUX and an inverter
• 2 8x1 MUX and 1 2x1 MUX    

8. How many 2:4 Decoders are needed to design 4:16 decoder ?

9. Add the two BCD number : 1001+0100 = 1101 (> 9), so add 6 to the result obtained as the maximum value in BCD is 9.

1101+0110 = 0001 0011 (13)

10. A 3 digit decimal number requires 12 bits for representation in the conventional BCD format,

because 1 digit needs 4 bit , so 3 digit needs 3 x 4 = 12 bits.

Note : Maximum value of BCD is 9, the bits required to represent is 4 bit (1001).

11. Delay for 128 bit carry look ahead adder is 16 

12.A 2x1 MUX needs can be realised using AND,OR and NOT gate.

13 Delay for 128 bit Ripple carry adder is 256. 

14. XS3 code equivalent of 0110 (6) is 1001 (6+3=9)

15.The following logic diagram shows the structure of

Gray to Binary Converter.