Sequential Circuits MCQ Quiz - Objective Question with Answer for Sequential Circuits - Download Free PDF

Concept:

A JK flip-flop toggles its output on every clock pulse when both J and K are high.

Given configuration:

• J = 1 (logic high)
• K = Q′ (complement of Q)

This means K will be 1 when Q is 0, and K will be 0 when Q is 1.

Initial Condition:

Q = 0 (flip-flop is initially cleared)

Apply 6 Clock Pulses:

Final Output Sequence at Q:

0 1 1 1 1 1 → 011111

Concept:

A 4-bit Serial-In Parallel-Out (SIPO) Right Shift Register shifts bits to the right on each clock pulse. The MSB is filled from a serial input, which in this case is connected to the LSB output (feedback loop).

Final Answer: 0111 (Option 2)

Concept:

The circuit contains a T Flip-Flop (TFF) whose T input is selected via a 2:1 MUX. The selection line of the MUX is S.

We know that the behavior of a T Flip-Flop is as follows:

• If T = 0 → No change in Q (hold state)
• If T = 1 → Toggle the state of Q

The MUX selects between two inputs: i0 and i1. Let’s assume:

• i0 = 0 (for S = 0) → T = 0 → Q holds
• i1 = 1 (for S = 1) → T = 1 → Q toggles

State Behavior:

• When S = 0 → T = 0 → Q holds its current state
• When S = 1 → T = 1 → Q toggles (0 ↔ 1)

Transition Summary:

• If Q = 0 and S = 0 → Q remains 0
• If Q = 0 and S = 1 → Q toggles to 1
• If Q = 1 and S = 0 → Q remains 1
• If Q = 1 and S = 1 → Q toggles to 0

Answer:

Option 4: State transition diagram matches the toggling/hold behavior correctly

Explanation:

Flip-Flop Behavior:

Definition: A flip-flop is a basic digital memory circuit used to store a single binary value. It is a bistable multivibrator, meaning it has two stable states. Flip-flops are fundamental building blocks in digital electronics and are extensively used in sequential logic circuits, registers, counters, and memory devices. The type of flip-flop determines its behavior and how it handles the input signals to transition between states.

Correct Option Analysis:

The correct option is:

Option 4: T Flip-Flop

The T flip-flop, also known as the toggle flip-flop, is a type of flip-flop that toggles its output state whenever a triggering signal (clock pulse) is applied. The behavior of the T flip-flop can be described as follows:

• Operation: The T flip-flop has a single input labeled "T" (Toggle). If T = 1, the flip-flop toggles its current state (from 0 to 1 or 1 to 0) on the rising edge of the clock pulse. If T = 0, the state remains unchanged.
• Truth Table:

  Clock	T	Q (Current State)	Qnext (Next State)
  ↑	0	0	0
  ↑	0	1	1
  ↑	1	0	1
  ↑	1	1	0

• Behavior: The T flip-flop is widely used in applications like counters and toggling circuits because of its ability to change states with each clock pulse when T = 1.

Applications:

• Used in binary counters to divide the clock frequency.
• Employed in toggle switches for state-changing operations.
• Utilized in frequency division circuits.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: JK Flip-Flop

The JK flip-flop is a versatile flip-flop with two inputs, J and K. It behaves differently based on the combination of its inputs:

• J = 0, K = 0: No change in state.
• J = 0, K = 1: Reset the output to 0.
• J = 1, K = 0: Set the output to 1.
• J = 1, K = 1: Toggle the output state.

While the JK flip-flop can toggle like the T flip-flop, it requires both inputs to be active (J = 1, K = 1) for toggling. Therefore, it is not specifically defined as a T flip-flop.

Option 2: RS Flip-Flop

The RS (Reset-Set) flip-flop is one of the simplest types of flip-flops. It has two inputs, R and S:

• R = 0, S = 0: No change in state.
• R = 0, S = 1: Set the output to 1.
• R = 1, S = 0: Reset the output to 0.
• R = 1, S = 1: Undefined state (not allowed).

This flip-flop does not toggle its state based on a single input, making it different from the T flip-flop.

Option 3: D Flip-Flop

The D (Data) flip-flop is designed to store a single bit of data. It has one input, D:

• D = 0: The output is reset to 0 on the clock pulse.
• D = 1: The output is set to 1 on the clock pulse.

The D flip-flop simply transfers the input to the output on the clock edge, without any toggling behavior, unlike the T flip-flop.

Option 5: This option is irrelevant to the context provided.

Conclusion:

Among the given choices, the T flip-flop (Option 4) is the correct answer because it specifically toggles its output state on the clock pulse, matching the described behavior. Understanding the distinctions between different types of flip-flops is essential for selecting the appropriate type for specific applications in digital circuit design.

Explanation:

Latches and Flip-Flop:

• Latches and flip-flops are the basic elements to store 1-bit of data. Hence they are also known as a one-bit memory element.
• Latches change the output continuously when there is a change in the input, i.e. they are level triggered.
• Flip-flop is a combination of latch and clock. It changes the output that is adjusted by the clock.
• The main difference between a latch and a flip-flop is that a flip-flop has a clock signal, whereas a latch does not.
• We can say that a flip-flop without a clock is a latch.
• Latches are asynchronous, which means that the output of a latch depends on its input.
• Basically, there are 4 types of latches: SR latch, JK latch, D latch, T latch.

T flip flop

The "T Flip Flop" has only one input.

It has only two output states i.e. hold and toggle.

For T = 0, the output is Q_n (Hold state)

For T = 1, the output is  (Toggle state)

The output equation of the T flip-flop is:

Q_n+1 = T ⊗ Q_n

Concept:

A Johnson counter is a modified ring counter, where the inverted output from the last flip flop is connected to the input to the first.

The MOD of the Johnson counter is 2n if n flip-flops are used.

The circuit diagram for a 4-bit Johnson Counter is as shown:

Calculation:

Total number of states in 4-bit counter are: 2ⁿ = 2⁴ = 16

Total states in Johnson counter are: 2n = 2.(4) = 8

Unused states are 16 - 8 = 8

D flip flop:

D flip flop has only one input terminal. The output of the D flip flop will be the same as the input. Hence, it is used in delay circuits.

The circuit is as shown below.

Logic symbol:

Truth table:

Characteristic equation: Qn+1 = D

The D flip flop may be obtained from an S-R flip flop by just putting one inverter between the S and R as shown in the figure below.

S = R̅

The D flip flop may be obtained from a J-K flip flop by just putting one inverter between the J and K as shown in the figure below.

K = J̅

T flip flop:

T flip flop has only one input terminal. The output of the T flip flop will be toggled when the input is high on every new clock pulse. The output will be the same as the previous state when the input is low.

The circuit is as shown below.

Logic symbol:

Truth table:

Characteristic equation: Qn+1 = TQ̅­n + T̅Qn

The T flip flop may be obtained from a J-K flip flop by making both the inputs are the same i.e. J = K.

The correct answer is option 2): 4

Concept:

For a counter with ‘n’ flip flops:

• The total number of states = 2ⁿ (0 to 2ⁿ – 1)
• The largest number that can be stored in the counter = 2ⁿ – 1
• To construct a counter with any MOD number, the minimum number of flip flops required must  satisfy: Modulus ≤ 2ⁿ
• Where n is the number of flip-flops and is the minimum value satisfying the above condition.
• Note: A MOD-N counter is also called as a divide by N counter as the input frequency is divided by the number of states of the counter.

Calculation:

Number no. of flip – flops are required to construct mod-12 counter,

must satisfy: 2ⁿ ≥ 12 The minimum value of n satisfying the above is: n = 4

• Latches and flip-flops are the basic elements for storing information. They are made of logic gates.
• One latch or flip-flop can store a 1-bit of information.
• For latches, its input can affect the output as long as the enable signal is asserted (high).
• For flip-flop, its input can affect the output only when the enable signal changes (falling edge or rising edge).

The difference between latches and flip flops is shown

Latches	Flip Flops
Latches are building block of sequential circuits and they are built using logic gates	Flip flops are also building blocks of sequential circuits but they are made using latches
Latches continuously change the input and output changes correspondingly	Flip flop output changes only when the clock is applied
Latches are level sensitive	Flip flops are edge sensitive

Concept:

For a counter with ‘n’ flip flops:

• The total number of states = 2n (0 to 2n – 1)
• The largest number that can be stored in the counter = 2n – 1

To construct a counter with any MOD number, the minimum number flip flops required must satisfy:

Modulus ≤ 2n

Where n is the number of flip-flops and is the minimum value satisfying the above condition.

Calculation:

The total number of states required when n = 3:

23  ≥  8

The states will vary from (0 to 7)

So the maximum states possible for the counter will be 8.

Concept:

For a counter with ‘n’ flip flops:

• The total number of states = 2n (0 to 2n – 1)
• The largest number that can be stored in the counter = 2n – 1

To construct a counter with any MOD number, the minimum number flip flops required must satisfy:

Modulus ≤ 2n

Where n is the number of flip-flops and is the minimum value satisfying the above condition.

Calculation:

Given: 

n = 3

Modulus ≤ 2n

Modulus ≤ 2³

Modulus ≤ 8

The most appropriate answer is option 1 i.e. Mod 6.

Johnson Counter: 

A Johnson counter is a modified ring counter, where the inverted output from the last flip flop is connected to the input to the first.

The circuit diagram for a 4-bit Johnson Counter is as shown:

The MOD of the Johnson counter is 2n if n flip-flops are used.

For an n-bit counter, the total number of states possible is 2ⁿ. ∴ The number of unused states for a Johnson counter will be:

Unused = Total States possible - Mod of the counter

= 2n - 2n

The correct answer is option 4):(Multiplexer)

Concept:

• Combinational logic is a type of digital logic that is implemented by Boolean circuits, where the output is a pure function of the present input only.
• Sequential logic is a type of digital logic in which the output depends not only on the present input but also on the history of the output.
• Sequential logic has memory while combinational logic does not.
• Flip-flop, counter, and shift registers are sequential circuits whereas multiplexer, decoder, and encoder act like combinational circuits.
•  A multiplexer also known as a data selector, is a device that selects between several analog or digital input signals and forwards the selected input to a single output line. The selection is directed by a separate set of digital inputs known as select lines.
• The Multiplexer has shown as 

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Additional Information

•  A flip-flop is a sequential digital electronic circuit having two stable states that can be used to store one bit of binary data. Flip-flops are the fundamental building blocks of all memory devices.
• The counter is a sequential circuit consisting of a set of flip-flops which can go through a sequence of states. It is used to count the number of clock cycles. Since the clock pulses occur at known intervals, the counter can be used for measuring time such as period or frequency.
• A shift register is a type of digital circuit using a cascade of flip-flops where the output of one flip-flop is connected to the input of the next. They share a single clock signal, which causes the data stored in the system to shift from one location to the next.