# D Flip Flop

Prerequisite : Introduction to Sequential Circuit

Flip Flop is an electronic device or to be precise a kind of memory component that can hold one bit of data. A flip flop has two states, that is “SET” and “RESET”. Those states are represented with the binary values 0 and 1. The flip flop remains in its current state until its receives a signal that switches it to opposite state. A clock or pulse signal may “trigger” the flip flop to change state.

## D Flip Flop

D flip flop is an electronic devices that is known as “delay flip flop” or “data flip flop” which is used to store single bit of data.D flip flops are synchronous or asynchronous. The clock single required for the synchronous version of D flip flops but not for the asynchronous one.The D flip flop has two inputs, data  and clock input which controls the flip flop. when clock input is high, the data is transferred to the output of the flip flop and when the clock input is low, the output of the flip flop is held in its previous state.

## Working of D Flip Flop

D flip flop consist of a single input D and two outputs (Q and Q’). The basic working of D Flip Flop is as follows:

• When the clock signal is low, the flip flop holds its current state and ignores the D input.
• When the clock signal is high, the flip flop samples and stores D input.
• The value that was previously fed into the D input is reflected at the flip flop’s Q output.
• If D = 0 then Q will be 0.
• If D = 1 then Q will be 1.
• The Q’ output of the flip flop is complemented by the Q output.
• If Q = 0 then Q’ will be 1.
• If Q = 1 then Q’ will be 0.

Truth Table of D Flip Flop

## Characteristic Table of D Flip Flop

The characteristic table of the D flip flop displays the behavior of the flip flop for each combination of input and current state. The characteristic table for a D flip flop is as follows.

Characteristics table of D Flip Flop

• D is the input, and Q is current state, Qn + 1 is the next state outputs.
• Qn+1 will always be zero when D is 0, irrespective of current state of flip flop.
• When the input of the flip flop is 1,  next state of  flip flop will always be 1, regardless of the current state of flip flop.

## Characteristic Equation of D Flip Flop

The characteristics equation of D flip flop consist of a Boolean expression that explains the relationship between the input and output of the flip flop. The characteristic equation for a D flip flop is as follows.

Characteristics Equation of D Flip Flop

• Qn+1 represents the output of flip flop at the next clock cycle.
• Dn is the input to the flip flop at the current clock cycle, and n represents the current clock cycle.
• This characteristic equation of D flip flop states “that the output of the flip flop at the next clock cycle will be equal to the input at the current clock cycle“.

## D Flip Flop Excitation Table

Her, Qn represents the current state of the flip flop, and Dn represents the current input of the flip flop. Where as Qn+1 represents the next state of the flipflop.

• When the Qn is 0 and the Dn is also 0, then the Qn+1 becomes 0. This situation explains the condition of “hold” state.
• When the Qn is 0 but Dn is 1, then the Qn+1 becomes 1. This situation explains the condition of “reset” state.
• When the Qn is 1 but Dn is 0, then the Qn+1 becomes 0. This situation explains the condition of “hold” state.
• When the Qn is 1 and the Dn is also 1, then the Qn+1 becomes 1. This situation explains the condition of “reset” state.

## Advantages of D Flip Flop

• D flip flop is very simple to design.
• The computation speed of D flip flop is very fast compared to other flip flops.
• D flip flop requires very few components to design which makes it simple to understand.

## Disadvantages of D Flip Flop

• D flip flops are glitch prone. When input varies fast, flip flop output may glitch. Digital circuit glitches are hard to identify and fix.

## Types of D Flip Flop

• D Latch.
• EdgeTriggered D Flip Flop.

## Application of D Flip Flop

D flip flop is having numerous number of application in digital system is described as follows:

• Memory: D flip flop is used to create memory circuit for holding the data.
• Registers: D flip flop is used to create register, which can hold data in digital system. By using the D flip flop the designer can built any size of register as per the requirement.
• Counters: D flip flops are used to create the counters which counts the number of event occurred in the digital system.
• Synchronous System: D flip flop is having in developing the synchronous system.

## Conclusion

In this article, we discussed the basis of D flip flop with the working principle of the D flip flops. We have also discussed about the characteristic table of D flip flop and analysing the table we have derived the characteristic equation and the excitation table of the D flip flop. This article explains several advantages and disadvantages of D flip flop with the recent applications of the D flip flop.

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