D Flip Flop in Digital Electronics

The D flip flop is the most important flip flop in digital electronics. The both inputs of the flip flop. S & R, can never be equal one at the same time. To get this , we use a gated SR FF with an inverter between the inputs.

In digital electronics, a flip flop is a logic circuit that is used to store 1 bit of binary information. Therefore, the flip-flops are considered fundamental building block of digital storage devices.

Based on construction and design, several different types of flip-flops(FFs) are available such as SR , JK, T , and D FF. In this article, we will discuss D FF, its truth table, circuit diagram, and applications.

What is a D Flip Flop?

The D flip flop have only one input line D and two output lines Q and Q’. It also has a clock input line for triggering of the circuit.

The logic block diagram is shown in the following figure.

logic block diagram of a D flip flop

Here, it has an input line designated by the symbol D, where a binary input is applied. Another input line to the D FF is a clock signal, denoted by CLK. The signal is utilized to synchronize and trigger the flip-flop. The output Q is the normal output which determines the state of the flip-flop, while the output Q’ is the complemented output which is inversion of the normal output Q.

D Flip Flop Circuit Diagram

We can design a D FF using digital logic gates. The logic circuit diagram of a D flip-flop is shown below.

D Flip Flop Circuit Diagram

It is clear that we can design a D flip-flop by using five NAND gates. It is basically a NAND logic SR FF in which S is directly connected to D input and the R is connected to the D input through an invert gate.

Truth Table of D Flip-Flop

Truth table provides information about its operation for different values of input D. The truth table of D FF is shown in the below table.

Input (D)Next State (Qn+1)Comment

From the truth table of D flip-flop, it is clear that when the value of the input D is logic 0, the D FF enters to the reset state, and when the input D is logic 1, the FF goes into the set state.

Characteristic Table of D Flip-Flop

The characteristic table of a D FF provides information about transition of state as per the input signal. The characteristic table is given below:

Input (D)Previous State (Qn)Next State (Qn+1)

Characteristic Equation of D Flip Flop

We can use K-Map and characteristic table of D FF to derive its characteristic equation.

The K-map simplification of the characteristic table is shown below.

 K-map simplification of the characteristic table of D flip-flop

From the K-map simplification, we get the following expression as the characteristic equation.

 characteristic equation of D flip-flop.


The following are some major advantages of D flip flop.

  • It is simpler to design and use in digital circuits, as it has only one input line.
  • It does not have the problem of race condition due to absence of feedback loop.
  • It does not have any invalid state.
  • It consumes less power.


Some common applications of D FF are listed below:

  • Used in shift registers in digital systems.
  • Used to introduce a delay in a digital system.
  • Also used to design state machines.
  • For designing binary counters.

This is all about D flip-flop, its truth table, and applications. The D FF is a very simple circuit used to store binary information in digital systems.

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