# UPTU Previous Year Exam Papers

# B Tech 3rd Semester

# Digital Electronics 2011-12

**Note Attempt all questions. Each question carries equal marks.**

**1. Attempt any four parts of the following:**

(a) Represent decimal number “-13” in all four methods of negative binary number representation using eight bits.

(b) Perform the following subtraction using 2’s complement method:

(i) 01000-01001 (ii) 0011.1001-0001.1110

(c) Add the following numbers:

(i) (ABC)_{|6} + (CDE)_{]6}

(ii) (77)_{8} + (107)_{g}

(d) Detect and correct error (if any) in the following received even parity Hamming code word 00111101010. Also find out the correct message.

(e) Minimize the given Boolean function using K-Map and implement the simplified function using NAND gates only. F (A, B, C, D) = Sm (0,1,2,9,11,15) + d (8,10,14).

(f) Minimize the following function using Quine Me Clusky method: f (A, B, C, D) = Sm (0,2,3,6,7,8,9,10,13)

** 2. Attempt any two parts of the following : **

(a) Construct a BCD to excess 3 code converter with a 4 bit adder. What must be done to change the circuit to an excess 3 to BCD code converter ?

(b) What is magnitude comparator ? Design a three bit comparator circuit using logic gates.

(c) (i) Design a full subtractor circuit with a decoder and

two OR gates.

(ii) Implement the function: F(A,B,C) = A BC + A BC + ABC+ABC using 4 : 1 multiplexer using A and B variables to the selection lines.

** 3. Attempt any two parts of the following: **

(a) Draw RS flip-flop and write the characteristic table and characteristic equation for it. Explain how will you convert it into D flip-flop.

2(b) Design a circuit that implements the state diagram.

(c) Design a synchronous counter using J-K flip-flop for the following input sequences:

A | B | c |

0 | 0 | 0 |

0 | 0 | 1 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 0 | 1 |

1 | 1 | 0 |

0 | 0 | 0 |

**4. Attempt any two parts of the following :**

(a) What is ROM ? What are the various types of ROM ? Explain.KEC302/KIH-26661 ,

(b) What is the basic architecture of a PLA ? How is the capacity of a PLA specified ? How is it programmed ? Explain.

(c) Draw the logic configuration of four input and four output PAL and explain.

**5. Attempt any two parts of the following:**

(a) Differentiate between asynchronous and synchronous sequential circuit. Define fundamental mode of operation.

(b) Define critical race and non-critical race. Discuss the concept of non critical race with examples.

(c) Describe briefly the excitation table and output table of a fundamental mode asynchronous sequential circuit.