## Digital Electronics (BCA -106) -  Question Paper (2014)

Time: 3 Hours                                                                                              Max. Marks: 75
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Note: Attempt any five questions including Q No. 1 which is compulsory. Select one question from each unit.

Q1: (a) Explain Diode and Transistor as a switch with diagram and table. Give their merits. (5)

(b) Implement XOR gate using universal logic gates only.                                        (5)

(c) Explain Binary Divider using successive subtraction method.                            (5)

(d) What are the applications of Gray Codes and Excess-3 codes?                           (5)

(e) What are the advantages of PROM as compared to PLA and PLD?                   (5)

Q2: (a) Convert A.B.C + A.C expression in standard SOP form and standard POS form.        (6)

(b) Prove A + (BCD) = (A + B)(A+C)(A+D) using Boolean Laws. Also give steps to solve Boolean expression using K-map.                                                                                         (6.5)

Q3: (a) What is a logic family? Differentiate TTL and CMOS in terms of current and voltage parameters, Noise margin, fan-in and fan-outs.                                                     (6.5)

(b) Implement Y = (AB) + A + BC using NAND and NOR gates only.                (6)

Q4: (a) Show how a full adder can be converted to a full subtractor with addition of an inverter circuit.                                                                                                                      (6)

Q5: (a) i. Explain briefly the BCD to seven segment decoder.                                        (3.5)
ii. How does an encoder difer from a de-multiplexer? Give advantages of each.    (3)

(b) Draw the logic diagram of parity generator/checker. Explain its operation with the help of Truth Table.                                                                                                                         (6)

Q6: (a) Differentiate
i. Combinational and sequential logic.                                                 (3)
ii. Positive and Negative Edge Triggering                                            (3)

(b) Explain realization of JK flip-flop using D flip-flop. Also give four basic applications of flip-flops.                                                                                                                (6.5)

Q7: (a) Explain Bidirectional shift register using four D flip-flops and four input multiplexers with timing diagram.                                                 (7)
(b) Draw logic diagrams of serial to parallel data transfer register using JK flip-flop synchronous inputs.                                                               (5.5)

Q8: (a) Design a MOD-10 up-down counter.                             (6)
(b) How does the architecture of a PAL differ from a PROM? List the applications of PLAs. (6.5)

Q9: (a) Draw the logic diagram of a 4-bit binary ripple counter using flip-flops with trigger on negative-edge transition of clock with clock cycle.                                                 (6.5)

(b) Explain SRAM and DRAM with digrams                                                          (6)