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Latches

Updated: Aug 9, 2023

#Latch is a logic circuit and a fundamental building block of #digitalelectronics. Latches are sequential logic circuits that are used to store Binary information. Latches have two states, are High and Low states. As the Latches have two states they are also referred to as #Multivibrators.

Latches are level-sensitive which operate with enable signal. Latches store single-bit data until the device is set to one (1). Latches are widely used in computing as well as data storage.


Types of latches:


There are different types of Latches like SR Latch, Gated SR Latch, D Latch, Gated D Latch, JK Latch, and T Latch.


SR Latch:


SR Latch is a Set- Reset Latch. It is an #asynchronous device i.e., it works separately for control signals depending upon the S and R states. SR latch can be made using either two #NAND or two #NOR gates.


Circuit Diagram:


The circuit diagram of SR Latch is given below

SR Latch using NAND Gate
SR Latch using NAND Gate
SR Latch using NOR Gate
SR Latch using NOR Gate









Truth Table of SR Latch:


The truth table of SR Latch is given below

Set(S)	       Reset(R)		Q		(Q)'
 0		0	      Latch           Latch
 0		1		0		1	
 1		0		1		0		
 1		1		0		0

Gated SR Latch:


Gated SR Latch is a special type of SR Latch with three inputs Set, Reset and Enable. The Operation of this latch is enabled by the enable input. As it requires enable signal for its operation it is sometimes referred to as #synchronous SR latch.


Circuit Diagram:


The circuit diagram of the Gated SR Latch is given below

Gated SR Latch using NOR Gate
Gated SR Latch using NOR Gate
Gated SR Latch using NAND Gate
Gated SR Latch using NAND Gate

Truth Table of Gated SR Latch:


The truth table of Gated SR Latch is given below


E or CLK        Set(S)	  Reset(R)	Q	   (Q)'
  0              0          0	       Latch      Latch
  0              0	    1	       Latch      Latch	
  0              1	    0	       Latch      Latch		
  0              1	    1	       Latch      Latch
  1              0          0          Latch      Latch
  1              0          1            0          1
  1              1          0            1          0
  1              1          1            0          0


D Latch:


D Latch is a Data Latch that has only one input. The output of the D latch is the same as the Data input.


Circuit Diagram:


The circuit diagram of D Latch is given below


D Latch
D Latch

Truth Table of D Latch:


The Truth table of D Latch is given below


     Data(D)          Q		(Q)'
	0	      0	         1		
	1	      1	         0

Gated D Latch:


The gated D Latch has two inputs, they are data and enable. The output of the Gated D Latch is the same as data input if the enable is set to one else there is no change in the output.


The circuit diagram of Gated D Latch is given below


Circuit Diagram:


Gated D Latch
Gated D Latch


Truth Table of Gated D Latch:


D latch truth table is given below


Enable(E)      Data(D)          Q		(Q)'
  0		0	      Latch            Latch
  0		1	      Latch            Latch			
  1		0		0		 1		
  1		1		1		 0	 


JK Latch:


JK Latch is similar to RS latch which has two inputs, J and K. The difference between RS latch and JK Latch is that JK Latch has feedback from output to input while there is no feedback in the RS Latch.


Circuit Diagram:


The output of the JK Latch Toggles when both the inputs are high


JK Latch
JK Latch

T Latch:


T Latch is designed by shorting the inputs J and K of JK Latch. When the input of T Latch is high, the output toggles.


Circuit Diagram:


The circuit diagram of T Latch is given below

T Latch
T Latch

Advantages of Latches


The advantages of latches are

  • Latches are flexible to design compared to flipflops.

  • Latches are small and occupy less area.

  • Latches use less power.

  • Latches don't require a clock signal.

Disadvantages of Latches


The disadvantages of latches are:

  • There is a chance to affect to race around conditions.

  • Analysis of Latches is difficult as they are level sensitive.

Applications of Latches


Latches are used in digital circuits. Some of the applications of Latches are

  • They are memory elements that are used to store information in the form of bits.

  • They are used in computing.

  • They are used in circuits like power gating and the clock as storage devices.

 

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Author -

Written By: Nagapuri Swathi




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2 Comments


Informative and concise! LearnElectronics India always delivers quality content.

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Anushka Gupta
Anushka Gupta
Jul 20, 2023

I've always found latches a bit tricky to understand, but Learn Electronics India's blog made it so much clearer for me. The step-by-step approach and engaging writing style kept me hooked throughout. Great work.

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