D Flip Flop: Circuit, Truth Table, Working, Critical Differences

Content: D Flip Flop

D Flip Flop Introduction | D Flip Flop Theory

A flip flop is the fundamental sequential circuit element, which has two stable states and can store one bit at a time. It can be designed using a combinational circuit with feedback and a clock. D Flip-Flop is one of that Flip Flop that can store data. It can be used to store data statically or dynamically depends on the design of the circuit. D Flip-Flop is used in many sequential circuits as register, counter, etc.

What is D flip flop ? | What is D type flip flop ?

D flip flop Definition | Definition of D flip flop

D flip-flop or Data flip flop is a type of flip Flop that has only one data input that is ‘D’ and one clock pulse input with two outputs Q and Q bar. This Flip Flop is also called a delay flip flop because when the input data is provided into the d flip-flop, the output follows the input data delay by one clock pulse.

Full Form of D flip flop

D stands for Delay or Data in D flip-Flop.

D flip flop Diagram | D flip flop Logic Diagram  | D Flip Flop Circuit | D Flip Flop Circuit Diagram | D Flip Flop Circuit Design | D Type flip flop Circuit Diagram | D Flip Flop Logic Circuit

The given circuit represents the D flip-flop circuit diagram, where the whole circuit is designed with the help of the NAND gate. Here the output of one NAND gate is feed as one input to the other NAND gate, which forms a latch. Then, the latch is gated with two more NAND gates where D is one input and clock is the other input. 

d flip flop
Fig. Circuit diagram of the D flip-flop designed with NAND gate

The final output of the D flip-flop is Q and Qbar, where Qbar is always complementary to Q.

D Flip Flop Truth Table | D Type Flip Flop Truth Table | D Flip Flop Truth Table explanation | D Flip Flop Table |

What is D Flip Flop Truth Table ?

The truth table of the d flip flop shows every possible output of the d flip-flop with the all possible combination of the input to the d flip flop, where Clock and D is the input to the D flip-flop and Q and Qbar is the output of the D flip-flop.

CLOCKDQQbar
00NO CHANGENO CHANGE
01NO CHANGENO CHANGE
1001
1110

D flip flop Excitation Table | Excitation Table of d flip flop | Characteristic Table of D Flip Flop | D flip flop State Table

The exaltation table or state table shows the minimum input with respect to the output that can define the circuit. Which mainly represents a sequential circuit with its present and next state of output with the preset input and clock pulse. This table is also known as a characteristic table for D flip-flop.

DinCLKPresent state ‘Q’Next state ‘Q’
X000
X011
0100
0110
1101
1111

D flip flop Boolean Expression | D Flip Flop Equation | D Flip Flop Expression | D Flip Flop Logic | Characteristic Equation of D Flip Flop

The boolean expression of the D flip-flop is Q(t+1)=D because the next value of Q is only dependent on the value of D, whereas there is a delay of one clock pulse from input D to output Q.

d flip flop
Fig. K- map of input (D) and output (Q) of the D flip-flop

How D Flip Flop Works ?

Working of D flip flop | D Type Flip Flop Operation | D Flip Flop Operation | Operation of D Flip Flop | D type Flip Flop Explained | D Flip Flop Explained | D flip flop function

D Flipflop is a bi-stable memory element, which can store one bit at a time, either ‘1’ or ‘0’. When the D input is provided to the Flip Flop, the circuit check for the clock signal is the signal of the clock is high ( for level triggered d flip-flop) then with every clock pulse, the input D propagates to the output Q. 

For edge triggered flip-flop, the circuit check for the transition of clock pulse according to which the flip Flop propagates the input to the output; edge triggered can be positive edge triggered or negative triggered. Positive edge triggered D flip-flop changes its output according to input with every transition of the clock pulse from 0 to 1. As for the negative edge triggered D flip-flop changes its output according to input with every transition of the clock pulse from 1 to 0.

D flip flop Timing Diagram | D Flip Flop Waveform | D flip flop time diagram | Output Waveform of D flip flop | Timing Diagram D Flip Flop

As shown in the given figure, there is a clock pulse representation, with which D, which is the input to D flip-flop, and Q which is the output, is represented, where Qbar is the complement output of the output Q, here we see the timing diagram of a positive edge flip flop, that’s why here the output changes with every positive transition in the clock pulse according to the input.

D Flip Flop: Circuit, Truth Table, Working, Critical Differences
Fig. Timing or Waveform diagram of the D flip-flop (positive edge triggered).

D flip flop Block Diagram | Block Diagram of D flip flop

The diagram shown below is the block representation of the d flip-flop, where D is the input, the clock is another input to the Flip Flop, where a preset and clear signal is used to set or reset the output Q of the D flip-flop. 

What is D flip flop Symbol ?

D Flip Flop: Circuit, Truth Table, Working, Critical Differences
Fig. Block representation of the D flip-flop with preset and clear

D flip flop Clear and Preset | D flip flop Preset and Clear | D flip flop Preset Clear | Preset and Clear in D flip flop

The given figure is the block diagram of a D flip-flop having preset/set and rest / clear as additional input to the Flip Flop, where Preset/Set is used to set the output Q of the flip Flop set to 1. Rest/Clear is to set the output Q of the flip Flop to 0.

D Flip Flop: Circuit, Truth Table, Working, Critical Differences
Fig. Block diagram of the D flip-flop with preset/set and reset/clear

D flip flop with Set

D flip-flop can have set the input as a requirement, and it can change the output and set the output Q to 1. It can be synchronous or asynchronous, Synchronous when the output can change only with the clock pulse, asynchronous is when the output can be set to 1 at any point of time regardless of the clock pulse.

D flip flop with Reset | D flip flop with Clear | D flip flop with Reset Circuit

D flip-flop can sometimes reset / clear input only in addition to data input and clock input, resetting the output Q to zero of the d flipflop as a requirement. Reset/Clear be active low input or active high input depends on the Flip Flop design.

Asynchronous Set and Reset

D flip flop with Asynchronous Set and Reset | D flip flop with Asynchronous Preset and Clear

D flip-flop can have an asynchronous set/preset and reset/clear as input independent of the clock. That means the output of the Flip Flop can be set to 1 with preset or reset to 0 with the reset despite the clock pulse, which means the output can change with or without a clock, which can result in asynchronous output.

D flip flop with Asynchronous Reset | Asynchronous Reset D flip flop

D flip-flops can have asynchronous reset, which can be independent of the clock. Regardless of the clock, the reset can change the output Q to zero, which can cause asynchronous output.

D flip flop with Synchronous Reset | Synchronous Reset d flip flop

D flip-flop with synchronous reset means the output can reset to zero with the reset input but only with the clock, which makes the reset input dependent on the clock pulse; without clock pulse reset will not be able to set the output Q to zero, which will give you a synchronous output always.

D Flip Flop with Enable

Other than set/preset or reset/clear D flip-flop can have enabled as one input when enable is high, the Flip Flop can operate with the data input and clock input, but when the enable is low then regardless of any other input, the flip Flop stays in a hold state.

D Flip Flop: Circuit, Truth Table, Working, Critical Differences
Fig. Block representation of a D flip-flop with Enable

D flip flop with Enable Truth Table

EnableDQn
01NO CHANGE
00NO CHANGE
111
100
Table: D flip-flop truth table with enable input

 

D flip flop Truth Table with Preset and Clear |D flip flop with Preset and Clear Truth Table

PR (ACTIVE LOW)CLR(ACTIVE LOW)CLKDQQbar
01XX10
10XX01
00XXNOT DEFINEDNOT DEFINED
111110
111001
111XNO CHANGENO CHNAGE
Table: D flip-flop table with preset, clear and clock

D flip flop Truth Table with Clock and Reset

CLKRESETDQ
0XXNO CHANGE
11X0
1011
1000
Table: D flip-flop Truth table reset and clock input

D flip flop Asynchronous | Asynchronous D flip flop

When D flip-flop generates output independent of the clock signal, then the output produced may be asynchronous. It is mainly caused by an asynchronous set/preset or clear/reset signal, which can set or reset the output of the flip Flop at any intent of time, which disrupt synchronicity in the D flip-flop.

State Diagram for D Flip Flop | State Diagram D Flip Flop | D Flip Flop State Diagram

The state diagram is the representation of a different stable state with the transition between the states with the cause of transition. Here every stable state output of the D flip-flop is represented with a circle. In contrast, the transition between the state is represented by the arrow between the circle, which is leveled with the cause of the transition.

D Flip Flop: Circuit, Truth Table, Working, Critical Differences
Fig. State diagram of the D flip-flop

When the state changes from 0 to 1, it is caused by the input D, which is high, and when the output state is 0, and at the time D=0 that produces no change in the output, the arrow with D=0 starts with state 0 and also returns to state 0.

ASM Chart for D flip flop

An algorithmic state machine chart contains three blocks: state block, condition block, and conditional output box. The rectangle box represents one state; the diamond box is the condition box true or false if the condition decides the branch to follow.

D Flip Flop: Circuit, Truth Table, Working, Critical Differences
Fig. ASM (algorithmic state machine) chart representation of the D flip-flop

D flip flop schematic | D Flip Flop Schematic Circuit | D Type Flip Flop Schematic

The figure shows the schematic representation of the D flip-flop; the schematic diagram represents the procedure using abstract. 

Two diagrams show the working of the D flip-flop when the clock is high and another showing when the clock is low. When the clock is high, the input data passes through the circuit, but when the clock is low, the input can not pass through the circuit, which shows regardless of the change in input, there will be no change in output when the clock is low.

D Flip Flop: Circuit, Truth Table, Working, Critical Differences
Fig. Schematic diagram representation of the d flip-flop. one figure with clock pulse low and other with clock pulse high

Dynamic D flip flop

Flip Flop is generally a static storing device, but a dynamic flip flop can dynamically store data. In the given schematic diagram of a dynamic flip flop, we can see a capacitor connected to each stage. When there is no clock pulse for a long time, the capacitor’s charge can be lost. However, because of the presence of the capacitor, the circuit will be able to store data dynamically.

D Flip Flop: Circuit, Truth Table, Working, Critical Differences
Fig. A Schematic diagram of the Dynamic D flip-flop

Dynamic D flip-flop is designed for faster operation; the area covered by dynamic flip flop is less than that of a static flip flop.

D flip flop Metastability | Metastability in D flip flop occurs when

Metastability refers to the state where output is not deterministic. It can cause oscillation, unclear transitions in the circuitry. For example, flip Flop faces the problem of metastability; it happens to a flip flop when the clock pulse and data change at the same instate of time, which causes the result to behave unpredictably.

To avoid metastability in flip Flop the operation of flip Flop should operate considering the setup time and hold time of the Flip Flop. Still, metastability cannot be eliminated completely, but it can be minimized.

Application of D flip flop | Application of D flip flop in Digital Electronics | Use of D flip flop | Uses of d flip flop

Important applications of D flipflop listed as follows :

  • D flip-flop can be used to produce a controlled delay in the circuitry.
  • Used to design frequency divider circuity.
  • For creating counters.
  • For developing registers.
  • Used in pipelining.
  • For synchronization.
  • Can be used to avoid glitches.
  • Used to fix clock frequency as for the requirement of the circuitry.
  • Can be used for isolation.
  • As Toggle switch.
  • Can be used for Data transmission.
  • Sequence generator.
  • Can be used as a memory element.

Difference Between D and T flip flop | Difference Between T and D flip flop | Difference between D flip flop and T flip flop

D FLIP-FLOPT FLIP FLOP
The output of a d flip flop follows the input with a delay of one clock pulse.The output of T flip flop toggles with a high input with every clock pulse.
It is known as delay flip flopIt is known as toggle flip flop
With low input the output also changes to low with clock pulseWith low input the output does not change at all, it stays in hold state.

Difference Between D flip flop and JK flip flop | Difference Between JK and D flip flop | D flip flop vs JK flip flop

D flip-flopJ K flip flop
The output of a d flip flop follows the input with a delay of one clock pulse.The output of a J K flip flop sets to 1 with J and resets to 0 with R  when there is clock pulse.
It is known as delay flip flop.It is also called universal flip flop.
It has less number of input combinations.It has more number of input combinations.

Difference Between D latch and D flip flop

D latchD flip-flop
D latch is a gated SR latch, which do not have clock input D flip-flop is combination of D latch with clock input
Less complex circuitComplex circuit
D latch is has enable signal which can enable or disable the latch operationD flip-flop has clock signal which can hold or operated the flip flop when no set or reset input is available.
D latch can be active high input or active low input latch.D flip-flop in which data input is always active high, where set or reset input can be active high or active low input.
D latch is always a level triggered circuit.D flip-flop can be level triggered or edge triggered circuit.
Less number of transistor is required for design.More number of transistor is required for design.
Asynchronous in nature.Generally synchronous in nature.

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About Sneha Panda

D Flip Flop: Circuit, Truth Table, Working, Critical DifferencesI have graduated in Applied Electronics and Instrumentation Engineering. I'm a curious-minded person. I have an interest and expertise in subjects like Transducer, Industrial Instrumentation, Electronics, etc. I love to learn about scientific researches and inventions, and I believe that my knowledge in this field will contribute to my future endeavors.

LinkedIn ID- https://www.linkedin.com/in/sneha-panda-aa2403209/

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