Latch and Flip-Flop Explained | Difference between the Latch and Flip-Flop

Summary

This video from the 'All About Electronics' YouTube channel explores basic memory elements in sequential circuits, focusing on Latches and Flip-Flops. It explains that both can store one bit of information and are known as Bistable Multivibrators. The video distinguishes between Transparent Latches, which respond immediately to input changes, and Gated Latches that respond based on control input. It also contrasts these with Flip-Flops, which are Edge Triggered and respond only at clock transitions, highlighting their use in synchronous circuits.

Takeaways

• 😀 The video discusses basic memory elements used in sequential circuits, focusing on Latches and Flip-Flops.
• 🔍 Both Latches and Flip-Flops can store one bit of information, having two stable states, and are thus known as Bistable Multivibrators.
• 🔄 A Latch responds to input level changes immediately, making it an Asynchronous type of memory element.
• 👁️‍🗨️ Transparent Latches change their output state immediately with input changes, while Gated Latches require an enable input to be high to respond to input changes.
• 🔒 Gated Latches can act as Synchronous memory elements when a periodic clock signal is applied to the enable input, responding to input changes only when the clock signal is high.
• 🕒 The timing diagram illustrates how a Gated Latch behaves during on and off times of the clock signal, showing its level sensitivity.
• 🔄 Flip-Flops, unlike Latches, are Edge Triggered Memory Elements, responding to input changes only at the clock transition.
• ⏫ Positive Edge Triggered Flip-Flops respond to input changes at the Rising Edge of the clock signal, while Negative Edge Triggered Flip-Flops respond at the Falling Edge.
• 🔄 The output of a Flip-Flop retains its state until the next clock transition, regardless of input changes in between.
• 🔄 Gated Latches and Flip-Flops respond differently to the same input and clock signal due to their sensitivity to level changes versus edge transitions.
• 🛠️ Latches and Flip-Flops are implemented using LOGIC gates, and the video promises to cover their design in upcoming videos.

Q & A

What are the basic memory elements used in sequential circuits?

The basic memory elements used in sequential circuits are Latches and Flip-Flops.

What is the primary function of a memory element in sequential circuits?

The primary function of a memory element in sequential circuits is to store one bit of information, which can be either zero or 1.

What is another name for Latches and Flip-Flops due to their two stable states?

Latches and Flip-Flops are also known as Bistable Multivibrators due to their two stable states.

How does a Latch respond to input level changes?

A Latch responds to input level changes immediately, making it an Asynchronous type of memory element.

What is a Transparent Latch?

A Transparent Latch is a type of Latch that immediately responds to the change in the input level.

What is a Gated Latch and how does it differ from a Transparent Latch?

A Gated Latch is a Latch that becomes transparent based on the control input. Unlike a Transparent Latch, it only responds to input changes when the enable input is high.

How can a Gated Latch be used as a Synchronous memory element?

A Gated Latch can be used as a Synchronous memory element by applying a periodic clock signal to its enable input. It will respond to the input when the clock signal is high and retain its previous state when the clock signal is low.

What is the difference between a Latch and a Flip-Flop in terms of their sensitivity to input changes?

A Latch is a Level Sensitive Memory Element, responding to the level of the input signal, while a Flip-Flop is an Edge Triggered Memory Element, responding to the transitions (edges) of the clock signal.

What are the two types of Edge Triggered Flip-Flops based on their response to clock signal transitions?

The two types of Edge Triggered Flip-Flops are Positive Edge Triggered Flip-Flops, which respond to the Rising Edge of the clock signal, and Negative Edge Triggered Flip-Flops, which respond to the Falling Edge of the clock signal.

How can a Gated Latch be modified to function as a Flip-Flop?

A Gated Latch can be modified to function as a Flip-Flop by adding a clock transition circuit, which allows it to respond to the clock signal transitions rather than the clock signal level.

How are Latches and Flip-Flops implemented in practice?

Latches and Flip-Flops are implemented using LOGIC gates.

Outlines

00:00

🔌 Introduction to Memory Elements in Sequential Circuits

This paragraph introduces the fundamental memory elements, Latch and Flip-Flop, used in sequential circuits. It explains that these elements can store one bit of information, making them essential building blocks. Latches respond immediately to input level changes, while Flip-Flops require a clock signal to update their state. The paragraph also distinguishes between Transparent Latches, which always respond to input changes, and Gated Latches, which only respond when an enable input is high. The concept of a clock signal turning a Gated Latch into a Synchronous memory element is introduced, highlighting the importance of clock signals in controlling memory element behavior.

05:05

🕒 Understanding Latch and Flip-Flop Behavior with Timing Diagrams

This paragraph delves deeper into the behavior of Latches and Flip-Flops, particularly focusing on their response to clock signals. It explains that Flip-Flops can be either Positive Edge Triggered or Negative Edge Triggered, responding to the rising or falling edge of a clock signal, respectively. The paragraph uses timing diagrams to illustrate how a Gated Latch behaves as a Level Sensitive Memory Element when a periodic clock pulse is applied to its enable input, becoming transparent during the high clock signal and retaining its state during the low signal. In contrast, Flip-Flops are described as Edge Triggered Memory Elements, responding only at the clock transition. The paragraph concludes by noting that while Flip-Flops are typically used in Synchronous circuits, a Gated Latch can be modified to function as a Flip-Flop, setting the stage for further exploration in future videos.

Keywords

💡Memory Elements

Memory elements are fundamental components in sequential circuits that can store information. In the context of the video, they are essential for building more complex digital systems. The script discusses two types of memory elements: Latches and Flip-Flops, which are capable of storing one bit of information.

💡Sequential Circuits

Sequential circuits are a type of digital circuit whose output depends not only on the current input but also on the past inputs, essentially on the sequence of inputs. The video emphasizes the importance of memory elements in these circuits, as they are the building blocks that enable the storage of information.

💡Latch

A Latch is a type of memory element that can hold a single bit of data. The video describes two types of Latches: Transparent Latches, which respond immediately to input changes, and Gated Latches, which respond based on a control input. Latches are crucial in the video as they illustrate the concept of level-triggered memory elements.

💡Flip-Flop

A Flip-Flop is another type of memory element that can store one bit of information and is used in sequential circuits. Unlike Latches, Flip-Flops respond to input changes only at specific points in time, determined by the clock signal. The video distinguishes Flip-Flops as edge-triggered memory elements, which can be either positive or negative edge triggered.

💡Bistable Multivibrator

Bistable Multivibrator is a term used to describe a device that has two stable states, which is a characteristic of both Latches and Flip-Flops. In the video, this term is used to highlight the ability of these memory elements to store information in one of two states, zero or one.

💡Transparent Latch

A Transparent Latch is a specific type of Latch that immediately reflects changes in its input on its output. The video uses this term to explain how Latches can be used in circuits that require immediate response to input changes, making them a key component in asynchronous operations.

💡Gated Latch

A Gated Latch is a type of Latch that becomes transparent to input changes only when a control signal, typically an enable input, is high. The video explains that when this enable input is low, the Gated Latch retains its previous state, illustrating the concept of a level-sensitive memory element.

💡Clock Signal

The Clock Signal is a periodic signal used in synchronous circuits to synchronize the operation of various components. In the video, the clock signal is used to control when Gated Latches and Flip-Flops respond to input changes, making it a central concept in the discussion of synchronous memory elements.

💡Edge Triggered

Edge Triggered refers to the behavior of a device that responds to input changes at specific transitions of a clock signal. The video uses this term to describe Flip-Flops, which can be either Positive Edge Triggered or Negative Edge Triggered, depending on whether they respond to the rising or falling edge of the clock signal.

💡Logic Gates

Logic Gates are the basic building blocks of digital circuits that perform logical operations. The video mentions that Latches and Flip-Flops are implemented using Logic Gates, indicating that these memory elements are constructed from simpler components that perform basic logical functions.

💡Synchronous Circuits

Synchronous Circuits are digital circuits that operate in a coordinated manner based on a common clock signal. The video discusses how Flip-Flops, which are edge-triggered, are typically used in synchronous circuits, contrasting them with the level-triggered Latches.

Highlights

Introduction to basic memory elements used in sequential circuits.

Memory elements are essential building blocks of sequential circuits.

Two types of memory elements: Latch and Flip-Flop.

Both Latch and Flip-Flop can store one bit of information.

Latch and Flip-Flop are also known as Bistable Multivibrators.

Latch responds to input level change immediately.

Transparent Latch is an Asynchronous type of memory element.

Gated Latch becomes transparent based on control input.

Gated Latch can be used as a Synchronous memory element with a periodic clock signal.

Gated Latch is sensitive to the clock signal level.

Flip-Flop is an Edge Triggered Memory Element.

Flip-Flop can respond to input at the Rising or Falling Edge of the clock signal.

Positive Edge Triggered Flip-Flop follows input at the Rising Edge.

Negative Edge Triggered Flip-Flop follows input at the Falling Edge.

Gated Latch and Flip-Flop respond differently to the same input and clock signal.

Flip-Flop is typically used as the Memory element in Synchronous circuits.

Gated Latch can be modified to function as a Flip-Flop.

Latches and Flip-Flops are implemented using LOGIC gates.

Upcoming videos will cover the design of transparent Latch and gated latch using LOGIC gates.

Transcripts

Hey, friends welcome to the YouTube channel  ALL ABOUT ELECTRONICS. So in this video,  

we will learn about the basic memory elements.  Which are used in the sequential circuits.  

So in the previous video, we have seen that, this  memory element is very essential and the basic  

building block of any sequential circuits.  So basically there are two types of memory  

elements, which are used in the sequential  circuits. That is Latch and the Flip-Flop.  

Well, both the memory elements are able to store  one bit of information. That means, their output  

can be either zero or 1. And since they have the  2 stable states, so they are also known as the  

Bistable Multivibrator. So in this video, let  us understand what is Latch and Flip-Flop,  

and what is the basic difference between two of  them. So first of all let's start with the Latch.  

So this Latch responds to the input level change  immediately. For example, let's say initially the  

input of this latch is equal to 1. And based on  that the stored value in the Latch is equal to 1.  

Now suddenly, if the input level changes to 0 then  the Latch will also immediately respond to that  

input level change. And based on that change, it  will also change the output stage. So basically,  

it is the Asynchronous type of memory element. So  this type of Latch, which immediately responds to  

the change in the input, are called Transparent  Latch. Now there is another type of Latch which  

becomes transparent, based on the control input.  So this Latches are known as the Gated Latch.  

So as you can see, this Gated Latch also has  enable input. So when this enable input is high,  

then this Latch is transparent to the input.  That means, when this enable input is high,  

then the Latch responds to the change in the input  immediately. And when this enable input is low,  

then even if the input changes, then it does not  respond to that input change. And in that case,  

it retains its previous state. Now, when we apply  the periodic clock signal to this enable input,  

then the same Gated Latch can be used as the  Synchronous memory element. Because now this latch  

will respond to the input, when the clock signal  is high. And it will remain in its previous state,  

when this clock signal is low. So as you can see,  basically it is sensitive to the clock signal  

level. But during this on time of the clock, if  the input level changes, then it will respond to  

that change immediately. So let us understand the  working of this Gated Latch with the help of the  

timing diagram. So let's see here, we have one  Gated Latch and the clock signal is applied as  

the enable input. So here, the signal which is  shown in the blue color is our clock signal. And  

that signal is applied at the enable input. So as  you know this Gated Latch will become transparent,  

when the clock signal is high. Or in other words,  when this enable input is high. So as you can see,  

during the on time of this clock signal, when  the enable input is high, then the output  

of the Latch is same as the input signal. And  after that, when this enable input becomes low,  

then even if the input signal changes, then also  this Latch will not respond to that input change.  

And as you can see, it is retaining its previous  state. So in this case, during the off time it  

will remain zero. Now once again, during the  on time of the clock when the enable input  

becomes high, then once again the output will  follow the input signal. So as you can see,  

during this time, this output is following the  input signal. And once again, during the off time  

of the clock signal, it will retain its previous  state. So as you can see, during this off time,  

the input is going from high to low. But still  this Latch will not respond to that input change.  

And it will retain its previous state. Now once  again, it will become transparent to the input,  

when the clock signal is high. Or in other  words, once again when the enable input is high.  

So at that time since the input is  low, so the output will also become  

low. So this is the output of this Gated Latch.  And as you can see, when this periodic clock pulse  

is applied at the enable input, then this Gated  Latch will become Level Sensitive Memory Element.  

That means, it will become transparent, when  this clock signal is high. On the other end,  

if you see the Flip-Flop then, it also has  clock input. And it responds to the input,  

only at the clock transition. That means, the  Flip-Flop is the Edge Triggered Memory Element.  

On the other end, if you see the Latch,  then it is the Level Triggered Memory  

Element. Now this Flip-Flop can respond  to the input, either at the Rising Edge,  

or the Falling Edge of the clock signal. So if  it responds to the input, at the Rising Edge,  

then it is called as the Positive Edge Triggered  Flip-Flop. On the other end, if it responds to the  

input at the Falling Edge of the clock, then it  is called as the Negatives Edge Triggered Flip-Flop.  

So through the timing diagram, let us understand,  how this is Edge triggered Flip-Flop behaves to the  

input level changes. And first let's take the  case of the Positive Edge Triggered Flip-Flop.  

So here, the same signal, which we have applied to  the Gated Latch, is also applied to the Flip-Flop.  

And this signal which is shown in the blue color,  is our clock signal. So since the Flip-Flop is the  

Edge Triggered Flip-Flop, so it will respond  to the input at the Rising Edge of the clock.  

And here, we are assuming that at the clock  transition the Flip-Flop follows the input signal.  

That means, at the clock transition, if the input  is high, then the output of the Flip-Flop is also  

high. And if the input is low, then the output of  the Flip-Flop will also become low. So based on  

that assumption, let us see what will be the  output of this Flip-Flop. So as you can see,  

at the first Rising Edge, the input is high.  That means, the output will also become high.  

But, now the Flip-Flop will respond to the  input, at the next Rising Edge. And till that,  

it will retain its previous state. That means  in this case, until the next Rising Edge,  

it will remain high. That means up to this  point, the output of the Flip-Flop will remain  

high. Now once again, at the next Rising Edge,  the input is once again high. That means during  

the next clock transition also the output  will remain high. And it will remain high,  

until the next clock transition. So in between,  even if the input level changes, then also it will  

not respond to that input level change. So now at  the next clock transition, since the input becomes  

low, so the output will also become low. And it  will remain low, till the next clock transition.  

So as you can see, this is the output of  this Positive Edge Triggered Flip-Flop.  

Similarly, for the same inputs let's see the  output of this Negative Edge Triggered Flip-Flop.  

So this Negative Edge Triggered Flip-Flop,  will respond to the input at the Falling Edge.  

So till the first Falling Edge, the output of  the Flip-Flop will remain zero. Now at the first  

Falling Edge, if you see then the input is low.  That means the output of the Flip-Flop will also  

remain low. And it will remain in this state,  until the next Falling Edge. Now once again  

at the next Falling Edge if you see, then the  input becomes high. So since the input is high,  

so the output will also become high. And it will  remain in this state, until the next Falling Edge.  

So in between the two Falling Edges, even if the  input level changes, then also this Flip-Flop  

will not respond to that input level change.  And at the next clock transition if you see,  

then the input becomes low. That means now, the  output of the Flip-Flop, will also become low.  

So overall, this is the output of this Negative  Edge Triggered Flip-Flop. So as you can see,  

for the same input and the clock signal the Gated  Latch and the Flip-Flop responds differently.  

Because this Flip-Flop is the Edge sensitive, but  the Latch is the level sensitive. So typically,  

in the Synchronous circuits, this Flip-Flop is  used as the Memory element. And in fact with the  

little modification, the Gated Latch can be  used itself as the Flip-Flop. For example if  

we add the clock transition circuit to this Gated  Latch, then the same can be used as the Flip-Flop.  

So in the upcoming videos, we will also learn  about that. But first it is good to know the  

basic design of the Latch. So this Latches and  Flip-Flops are implemented with the help of the  

LOGIC gates. So in the next video, we will learn  that, how to design the transparent Latch as well  

as the gated latch with the help of the LOGIC  gates. But I hope in this video you understood  

what is Latch and Flip-Flop. And what is the basic  difference between the Latch and the Flip-Flop.  

So if you have any question or suggestion, then do  let me know here in the comment section below. If  

you like this video, hit the like button and  subscribe the channel for more such videos.