What is the Difference Between Latch and Flip Flop

The main difference between latch and flip flop is that the latch checks the input continuously and changes the output when there is a change in the input. In contrast, the flip-flop is a combination of a clock and a latch, and its output is changed according to the clock when there is a change in the input.

Flip-flops and latches are circuit elements that can store information. It is possible to store one bit of data in one latch and flip-flop.

Key Areas Covered

1. What is a Latch
     – Operation, Input, Output
2. What is a Flip Flop
     – Operation, Input, Output
3. What is the Difference Between Latch and Flip Flop
     – Comparison of Key Differences

Key Terms

Circuit, Flip Flop, Latch

What is a Latch

Laches work in an asynchronous manner. In other words, the output the latch produces will depend on the input. Most of the computers today are synchronous. The output of these sequential circuits in computers are capable of changing simultaneously with a global clock signal.

Figure 1: SR Latch

There are four types of latches as T, D, SR, and JK latches.

What is a Flip Flop

A flip flop can be designed using a NAND gate or a NOR gate. Thus, a flip flop will have two inputs, two outputs and a set and reset. This type of flip flop is known as an SR flip flop.

Figure 2: SR Flip Flop

Flip flops are capable of storing binary values. They will have an additional clock signal which makes it function very differently when compared with a latch.

Difference Between Latch and Flip Flop

Structure

Latches are built by using logic gates while flip-flops are built using latches in addition to a clock signal.

Operation

There is a distinct difference between latch and flip flop based on their operation. Latch checks input continuously and changes output correspondingly whereas flip flop checks input continuously but, changes the output in a corresponding manner with the clock signal.

Sensitivity

The latch is sensitive to the input switch and is capable of transmitting data as long as the switch is in on-state. On the other hand, the flip-flop,  is sensitive to the clock signal, and the output will not change until a change occurs in the input clock signal. 

Binary Input

Another difference between latch and flip flop is that latches work with only binary inputs while flip-flops work with binary inputs as well as the clock signal.

Trigger

Latch is level triggered as the output will only change with the change in the binary level. Flip flops, on the other hand, are edge triggered and the output will change based on the positive edge or the negative edge of the clock signal.

Role as a Register

Latches cannot be used as a register due to the lack of a clock signal. However, flip-flops are capable of working as registers as they come with a clock. Therefore, this also a difference between latch and flip flop.

Synchronous Nature

Moreover, latches are not synchronous as they cannot work based on the time signal. But, flip flops are synchronous as they work based on the clock signal.

Conclusion

Flip-flops and latches are circuit elements that can store information. In brief, the main difference between latch and flip flop is their method of operation. Latch checks input continuously and changes output correspondingly while, the flip flop checks input continuously but changes the output in a corresponding manner with the clock signal.

Image Courtesy:

1. “Transistor Bistable interactive animated-en” By DrJolo – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “SR (Clocked) Flip-flop Diagram” By Inductiveload – Own Drawing in Inkscape 0.43 (Public Domain) via Commons Wikimedia