Question 1 |

A sequence detector is designed to detect precisely 3 digital inputs, with overlapping
sequences detectable. For the sequence (1,0,1) and input data (1,1,0,1,0,0,1,1,0,1,0,1,1,0):

what is the output of this detector?

what is the output of this detector?

1,1,0,0,0,0,1,1,0,1,0,0 | |

0,1,0,0,0,0,0,1,0,1,0,0 | |

0,1,0,0,0,0,0,1,0,1,1,0 | |

0,1,0,0,0,0,0,0,1,0,0,0 |

Question 1 Explanation:

Given overlapping sequence input data = 11010011010110

It will give output 1 when 101 is detected.

\begin{aligned} 110 - 0\\ 101 - 1\\ 010 - 0\\ 100 - 0\\ 001 - 0\\ 011 - 0\\ 110 - 0\\ 101 - 1\\ 010 - 0\\ 101 - 1\\ 011 - 0\\ 110 - 0\\ \end{aligned}

So, output = 010000010100

It will give output 1 when 101 is detected.

\begin{aligned} 110 - 0\\ 101 - 1\\ 010 - 0\\ 100 - 0\\ 001 - 0\\ 011 - 0\\ 110 - 0\\ 101 - 1\\ 010 - 0\\ 101 - 1\\ 011 - 0\\ 110 - 0\\ \end{aligned}

So, output = 010000010100

Question 2 |

Which one of the following statements is true about the digital circuit shown in the figure

It can be used for dividing the input frequency by 3. | |

It can be used for dividing the input frequency by 5. | |

It can be used for dividing the input frequency by 7. | |

It cannot be reliably used as a frequency divider due to disjoint internal cycles. |

Question 2 Explanation:

So, frequency will be divided by 5.

Question 3 |

For the synchronous sequential circuit shown below, the output Z is zero for the initial
conditions Q_{A}Q_{B}Q_{C}=Q_{A}'Q_{B}'Q'_{C}=100

The minimum number of clock cycles after which the output Z would again become zero is ________

The minimum number of clock cycles after which the output Z would again become zero is ________

4 | |

5 | |

6 | |

7 |

Question 3 Explanation:

The output Z will again become zero after 6th clock cycle.

Question 4 |

The current state Q_{A}Q_{B} of a two JK flip-flop system is 00. Assume that the clock rise-time is much smaller than the delay of the JK flip-flop. The next state of the system is

00 | |

01 | |

11 | |

10 |

Question 4 Explanation:

From the figure we get

J_A=K_A=1

J_B=K_B=\bar{Q_A}

So, next state will be 11.

J_A=K_A=1

J_B=K_B=\bar{Q_A}

So, next state will be 11.

Question 5 |

In the following sequential circuit, the initial state (before the first clock pulse) of the circuit is Q_{1}Q_{0}=00. The state (Q_{1}Q_{0}), immediately after the 333^{rd} clock pulse is

00 | |

01 | |

10 | |

11 |

Question 5 Explanation:

From the circuit, we can find out that

J_0=Q'_1,\;K_0=Q_1

J_1=Q_0,\;K_1=Q'_0

So state diagram is

at every 4th clock, the system is at 00

So, at 332 it will be at 00

So, at 333 clock it will be at 01.

J_0=Q'_1,\;K_0=Q_1

J_1=Q_0,\;K_1=Q'_0

So state diagram is

at every 4th clock, the system is at 00

So, at 332 it will be at 00

So, at 333 clock it will be at 01.

Question 6 |

The figure shows a digital circuit constructed using negative edge triggered J-K flip flops. Assume a starting state of Q_{2}Q_{1}Q_{0}=000. This state Q_{2}Q_{1}Q_{0}=000 will repeat after _______ number of cycles of the clock CLK

4 | |

5 | |

6 | |

7 |

Question 6 Explanation:

JK flip-flop1 and 2 from a syncgronous sequential circuits and they are synchronized with the output of 0th JK flip-flop.

Number of cycles = 3 i.e. equal to 6 clock cycles.

Number of cycles = 3 i.e. equal to 6 clock cycles.

Question 7 |

A state diagram of a logic gate which exhibits a delay in the output is shown in
the figure, where X is the don't care condition, and Q is the output representing
the state.
The logic gate represented by the state diagram is

XOR | |

OR | |

AND | |

NAND |

Question 7 Explanation:

If any one of the input is zero, output is 1 and for both inputs as '1' , output is '0', which represents the NAND gate.

Question 8 |

A JK flip flop can be implemented by T flip-flops. Identify the correct implementation.

A | |

B | |

C | |

D |

Question 8 Explanation:

To obtain a JK flip-flop from a T flip-flop, we first constuct the characteristic table of JK flip-flop, and then obtain the excitation values for the T flip-flop as shown below

Now, assuming T to be an output, we solve it in terms of J, K, Q_n inputs. This gives the defination of the logic to be applied on the T input.

Also, observing the given options, we solve for T using a maxterms map instead of using a minterms map, as shown below

T=(J+Q_n)\cdot (K+\bar{Q_n})

The circuit corresponding to this expression is given in option (B).

Now, assuming T to be an output, we solve it in terms of J, K, Q_n inputs. This gives the defination of the logic to be applied on the T input.

Also, observing the given options, we solve for T using a maxterms map instead of using a minterms map, as shown below

T=(J+Q_n)\cdot (K+\bar{Q_n})

The circuit corresponding to this expression is given in option (B).

Question 9 |

A cascade of three identical modulo-5 counters has an overall modulus of

5 | |

25 | |

125 | |

625 |

Question 9 Explanation:

Overall modulus =5 x 5 x 5=125

Question 10 |

The clock frequency applied to the digital circuit shown in the figure below is
1 kHz. If the initial state of the output Q of the flip-flop is '0', then the frequency of
the output waveform Q in kHz is

0.25 | |

0.5 | |

1 | |

2 |

Question 10 Explanation:

x=\overline{(Q\oplus \bar{Q})\cdot (Q \odot \bar{Q})}

\;\;=\overline{1\cdot 0}=1

\because \;\; X=1=T \Rightarrow Q always toggle whenever clock triggers.

\therefore \; f_Q=\frac{f_{clk}}{2}=\frac{1kHz}{2}=0.5kHz

\;\;=\overline{1\cdot 0}=1

\because \;\; X=1=T \Rightarrow Q always toggle whenever clock triggers.

\therefore \; f_Q=\frac{f_{clk}}{2}=\frac{1kHz}{2}=0.5kHz

There are 10 questions to complete.