Difference Between Latch and Flip-Flop (With Table)

In the field of electronic and digital engineering, we come across many types of circuits and circuital elements. Latches and flip flops are the fundamental skeletons of sequential logic circuits. The basic unit of constructing a functional logic circuit is a ‘gate’, and these gates are used for the creation of logic circuits i.e: latches and flip-flops. And, flip-flops can even be created using the combination of latches but the vice versa is not possible.

The outputs of latches and flip-flops depend on all the previous inputs as well as outputs. However, they might look fundamentally similar, there are quite many differences between latches and flip-flops.

Latch vs Flip-Flop

The difference between latch and flip flop is that, a latch logic circuit does not consist of a clock signal whereas, a flip-flop circuit’s output is defined by a clock signal. These logic circuits are considered as memory storage elements and are used in computers and many other systems. They are used as data storage elements in a circuit. Both are bistable devices that are represented as 0 or 1.

A latch is an electronic circuit (logic circuit) that has two different inputs and one output. The two inputs are termed as ‘SET’ and ‘RESET’. Latches are either considered as active-high circuits; when both the inputs are tied to ground and a momentarily HIGH signal is induced in either of the input or active-low circuits; when the inputs are HIGH themselves and a momentary low signal is triggered at any of the inputs.

A flip-flop is synchronous because it has a clock signal, unlike a latch circuit. Flip-flop is a basic digital memory storage circuit, used in the construction of complex sequential circuits. The first flip-flop structure was used back in 1943 in a British Colossus computer. A flip-flop is frequently referred to as a bistable multivibrator and is used as a key element in making a complex sequential logic circuit.

Comparison Table Between Latch and Flip-Flop

Parameters of comparisonLatchFlip-Flop
Input-Output ResponseA latch checks the inputs continuously and simultaneously responds to the inputs ie; SET or RESET.A Flip-Flop checks the inputs but changes the output only when defined by the clock signal or any other induced signal.
TypesNo classifications of latch circuits.Flip-flops are of two types: synchronous or asynchronous flip flops.
Clock SignalNo clock signal is present in this type of circuit.A clock signal is present in all flip flop circuits.
UsageThese can be used for the designing of sequential circuits but are usually not preferred.They are the building blocks of widely used sequential circuits like counters.
ExamplesSR Latch, D Latch.D Flip-flop, JK Flip-flop.

What is Latch?

A latch is a very commonly discussed logical circuit that is used in designing a sequential circuit and is also known as a SET-RESET circuit. Latch circuits are made using gates like NOR, AND, NAND, etc. The two inputs are termed SET and RESET. The difference in the inputs and outputs derives from the type of latch circuit it is.

For example, if SET and RESET of the circuit are connected to ground (Low) and the latch is triggered momentarily by a HIGH signal on either of the inputs, it will be referred to as an active-high circuit. Similarly, if the two inputs are simply High, and the latch is triggered by a momentary LOW signal on either input, it will be called an active-low circuit.

Latch circuits respond instantaneously upon the two inputs, unlike a flip flop which is equipped with a clock signal. They are also used to make flip-flop circuits that are either synchronous or asynchronous in nature. Some examples of Latch circuits are SR Latch and D Latch.

What is Flip-Flop?

Just like a latch logic circuit, a flip flop has two stable states (1 and 0) and is used to store state information. A flip-flop is used as the memory storage element in a sequential circuit. It also has a clock signal that affects the change in output.  Just like a latch logic circuit, a flip flop has two stable states (1 and 0) and is used to store state information. A flip-flop is used as the memory storage element in a sequential circuit. It also has a clock signal that affects the change in output.

The output in a sequential circuit is either made up of gates that build a combinational circuit or flip-flops or the combination of both the circuital elements. The state of the flip-flop is influenced by the clock signal pulse and is off when the clock pulse isn’t active. The state of the flip-flop is influenced by the clock signal pulse and is off when the clock pulse isn’t active.

Usually, a clocked flip-flop serves as the memory element in a synchronous sequential circuit and similarly, an un-clocked flip-flop (ie; latches) serves as a memory element in an asynchronous sequential circuit. Flip flop circuits are nowadays more preferred in modern computers and memory storage-based sequential circuits when compared to the asynchronous latch circuits.

A flip-flop is an edge-triggered device built using gates like NOR, NOT, AND, NAND. Also, flip flops can be built using asynchronous latch circuits just like gates are used in building a latch circuit. Some examples include D flip-flop and JK flip-flop.

Main Differences Between Latch and Flip-flop

  1. A flip-flop is synchronous whereas a latch logic circuit is asynchronous. When constructing a memory logic circuit, gates and flip-flops are preferred over latches because of its edge-triggered property.
  2. Flip-flops are equipped with a clock signal but latches do not have a clock signal.
  3. A latch is a level-triggered device whereas, a flip flop is an edge-triggered device.
  4. Flip-flops are considered as the building blocks of sequential circuits with memory storage but latches aren’t preferred much. However, sometimes latches can be used for designing a sequential circuit.
  5. Flip-flops can be built using gates and latches but latches cannot be built using flip-flops. However, gates are common building blocks for both circuits.

Conclusion

Latches and flip-flops are both bistable devices with stable states are represented as 0 and 1. Both logical circuits are derived by the combinations of various gates.  These are basic memory elements in a sequential logic circuit.

A flip flop is considered more efficient than a latch because it is equipped with a clock pulse signal that defines the output results. A flip-flop circuit is used mostly in modern computer circuits and other sequential circuits like counters. Data storage is the functionality of both the circuital elements and these types of circuits are collectively known as the building blocks of a sequential logic circuit.

References

  1. https://dept-info.labri.fr/~strandh/Teaching/AMP/Common/Strandh-Tutorial/flip-flops.html
  2. https://www.elprocus.com/digital-electronics-flip-flop-circuit-types-and-applications/

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