## Combinational-Circuits

Question 1 |

In the following truth table, V = 1 if and only if the input is valid.

What function does the truth table represent?

Priority encoder | |

Decoder | |

Multiplexer | |

Demultiplexer |

Question 1 Explanation:

It is a 2

^{2}× 2 encoder. The inputs have priorities. So, it is a priority encoder.Question 2 |

The amount of ROM needed to implement a 4 bit multiplier is

64 bits | |

128 bits | |

1 Kbits | |

2 Kbits |

Question 2 Explanation:

To implement a 4-bit multiplier we need to store all the possible combinations of 2

Hence option D is the answer.

^{4}x 2^{4}inputs and their corresponding 8 output bits. The total ROM size needed = 2^{8}x 8 bits = 2^{11}bits = 2 Kbits.Hence option D is the answer.

Question 3 |

A circuit outputs a digit in the form of 4 bits. 0 is represented by 0000, 1 by 0001, ..., 9 by 1001. A combinational circuit is to be designed which takes these 4 bits as input and outputs 1 if the digit ≥ 5, and 0 otherwise. If only AND, OR and NOT gates may be used, what is the minimum number of gates required?

2 | |

3 | |

4 | |

5 |

Question 3 Explanation:

= A + BD + BC

= A + B (D + C)

So minimum two OR gates and 1 AND gate is required. Hence, in total minimum 3 gates is required.

Question 4 |

**The combinational circuit given below is implemented with two NAND gates. To which of the following individual gates is its equivalent?**

NOT | |

OR | |

AND | |

XOR |

Question 4 Explanation:

[(a.b)'. (a.b)' ]'= ((a.b)')' + ((a.b)')'

=(a.b)+(a.b)

=(a.b)

=(a.b)+(a.b)

=(a.b)

There are 4 questions to complete.