Digital circuits miscellaneous

Digital circuits miscellaneous

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Digital Circuits

Digital circuits miscellaneous
  1. The state transition diagram for the logic circuit shown is








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    Truth-table for D-type FF

    when A = 0, Y = X0 = Q
    A = 1, Y = X1 = Q,
    when
    Q = 0, A = 0, Y = X0 = Q = 1
    then, D = 1, Qn+1 = 1.
    Q = 0, A = 1, Y = X1 = 0
    then, D = 0, Qn+1 = 0
    Q = 1, A = 0, Y = X0 = 0
    then, D = 0, Qn+1 = 0
    Q = 1, A = 1, Y = X1 = 1
    then, D = 1, Qn+1 = 1.
    Hence, state diagram will be as in fig.(d).

    Correct Option: D

    Truth-table for D-type FF

    when A = 0, Y = X0 = Q
    A = 1, Y = X1 = Q,
    when
    Q = 0, A = 0, Y = X0 = Q = 1
    then, D = 1, Qn+1 = 1.
    Q = 0, A = 1, Y = X1 = 0
    then, D = 0, Qn+1 = 0
    Q = 1, A = 0, Y = X0 = 0
    then, D = 0, Qn+1 = 0
    Q = 1, A = 1, Y = X1 = 1
    then, D = 1, Qn+1 = 1.
    Hence, state diagram will be as in fig.(d).

  1. The output Y of the logic circuit given below is








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    y = x x + xx = x + x = 1

    Correct Option: A

    y = x x + xx = x + x = 1

  1. A two-bit counter circuit is shown below. If the state QAQB of the counter at the clock time tn is "10" then the state QAQB of the counter at tn + 3 (after three clock cycles) will be








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    Correct Option: C

  1. The truth table of a monoshot shown in the figure is given in the table below.

    Two monoshots, one positive edge triggered and other negative edge triggered, are connected as shown in the figure. The pulse widths of the two monoshot outputs, Q1 and Q2. are TON1 and TON2 respectively.

    The frequency and the duty cycle of the signal at Q1 will respectively be








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    From question,

    ƒ =
    1
    		, D =
    TON2
    TON1 + TON2TON1 + TON2

    Correct Option: B

    From question,

    ƒ =
    1
    		, D =
    TON2
    TON1 + TON2TON1 + TON2

  1. The figure shown a digital circuit constructed using negative edge triggered J-K flip flops. Assume a starting state of Q2Q1Q0 = 000. This state Q2Q1Q0 =000 will repeat after _______ number of cycles of the clock CLK








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    First flip flop acts as mod-2 counter Second 2 flip flops from mod (2n-1) Johnson counter = mod counter
    ∴ overall modulus = mod – 6 counter

    Correct Option: C

    First flip flop acts as mod-2 counter Second 2 flip flops from mod (2n-1) Johnson counter = mod counter
    ∴ overall modulus = mod – 6 counter