Theory:

What is Flip Flop:

A flip-flop is a circuit that maintains a state until directed by input to change the state. Flip-flop is popularly known as the basic digital memory circuit. It has its two states as logic 1(High) and logic 0(low) states. A flip flop is a sequential circuit which consist of single binary state of information or data. The digital circuit is a flip flop which has two outputs and are of opposite states. It is also known as a Bistable Multivibrator.

There many types of flip flops – like

a.  SR Flip Flop
          b.    JK Flip Flop
          c.    D Flip Flop
          d.    T Flip Flop
          

Here we’ll discuss with D Flip Flop only.

D Flip Flop:

The D Flip Flop Consists a single data input (D), a clock input (CLK) and two outputs: Q and Q’ (the complement of Q).

Given Below is the Diagram of D Flip Flop.

Fig1. D Flip Flop Diagram

A D type flip-flop, wherein data penetrates via rising or falling clock pulses and which is received on output, is called edge-triggered D flip-flop. Here is the activation diagram for a positive edge trigger flip-flop where input is D, clock pulse E and outputs are Q and ~Q.

Fig2. Activation Diagram of Positive Edge Trigger D Flip Flop

In this activation diagram, vertical pink lines are pointing out the time where there is a positive edge of the clock pulse.

• A> At the 1st pink line from left, when there is a positive edge of the clock pulse E, D is low. Hence output Q is low.
• B> At the 2nd pink line from left again there is a positive edge of the clock pulse E and D is low. Hence Q is still low.
• C> At the last pink line, again there is a positive edge of the clock pulse E and D is high. Hence Q is high.

The truth table of the positive edge trigger D flip flop is as below.

So the input state moves to output only when clock pulse is high. Otherwise the state of the flip flop does not change. The truth table is also a representation of Fig2.