What is a Clock?

welcome to lecture number 120 in digital electronics and this is the best time to find the answer for the question what is clock because we cannot start our flip-flop until and unless we know about the clock so let's start with it in sequential circuit there are many processes going on the output of a circuit is input of other and thus there should be control over the processes as they cannot operate randomly so we need clocking to time this circuit in other words we need a sequence of this circuit okay it is called cloth because it

decides the time of the input like a common clock decides our daily routine we can decide the speed of the circuit by changing the clock frequency so what actually a clock is a clock is nothing but a signal that goes from low to high then again low and repeats so it is a signal which is having the duty cycle of 50% I will tell you what is duty cycle but let me first tell you about this clock you can see it is low at this starting so it is zero then it goes high becomes one

and the time for which it is high is equal to the time for which it is low okay and then again it becomes low for the same time and then again high and repeats so if I want to find out the time period of this clock let us say T then this will be the time period of this clock and let us say F is the frequency then frequency is equal to 1 by time period you already know this so frequency is 1 by capital T now if I want my circuit to work faster I

need to increase the frequency or I can say that I need to decrease the time period of the clock okay now this clock is given to the sequential circuit the same this is a sequential circuit and I assume it is an S our flip-flop so there will be s as the input R as the other input Q and Q Bar are the outputs now I will give klog as one of the input and I will call it CL K the short form for the clock now the circuit or you can say that the flip-flop will

work only when this clock is high it means it will be functional the flip form will be functional for this time only for this time but only for this one and for the next high pulses okay I hope it is clear to you in the same way you can also design your flip-flop to work when the clock goes from low to high I mean when the clock is here and it goes high during this time during this time particular time let me do it in different color during this particular time your flip-flop will be functional

similarly it will be function for this low to high this low to high okay this one is your leading edge we call it as edge degree in the next presentation we will see the triggering methods in that presentation you will have a better intuition of this all things and this one is called as the falling edge because it is the H when high is changing to your low okay so you can design your circuit in whatever manner you want it may be either working for the high pulse or from low to high pulse it can

also work from high to low pulse that we will see in the next presentation so I hope you are not getting what is the use of clock and why it is being used because we don't want our input to change randomly form because for a particular input the output is same and we want to use this output at particular time so we cannot let this output change randomly because there are so many processes so many stray signals are coming in this circuit and because of that our output may change so the clock is the one

which saves us from this condition okay so let's move to the another point that is our duty cycle you will very frequently use this thing in the digital electronics duty cycle the duty cycle is nothing but the ratio of the time the time for which the signal is high to the total time so it is very simple if I see in the clock it is high for the 50% of time if I say T is the total time for this particular signal then T is the total time and in this T if I see for

the time the clock is high it is 50% or I can say that T by 2 so it is T by 2 if I simplify this I will have 1 by 2 so duty cycle for the clock is 50% so this was a very simple presentation in the next presentation we will see the triggering mechanism that is also very important lecture before we proceed to our flip-flop so see you in the next one