Analog and Digital signals
Today our topic is very important about basic and hidden concept of analog and digital signals as we know that there are only two types of signals which are used in communication system any electronics devices use these signals for communication or exchange of information so it is very important to understand these two signals basic concept one is analog signal and other is digital signal in this post we will study hidden and depth concept of analog and digital signals after complete study of this post your all doubt and concept will be 100% clear for analog and digital signals before going to discuss analog signal and digital we will discuss first analog clock and digital clock see picture below.

analog and digital signals as from the above figure why one clock is called analog clock and other is called digital clock this is basic important point to understand in first clock analog we see that there are three hands one is hour hand second is minute hand third is second hand then we can say that this analog clock has time as hour:minute:second so it can take any value in 24 hour. now lets talk what happens in digital clock there is hour level and minute level as hour:minute there is no second level hence after 60 second pass minute level will change from 1 minute to 2 minute we can’t see what is going in between 1 minute to 2 minute because it is not allowed in digital clock only level 0,1,2,3,4,5,…minute not like 1 minute 30 second that is why it is digital because only level like 0,1,2,3,4,5,6….59 minute there is no any level between 1 to 2 minute like 1 minute 30 second hence in digital clock intermediate level is not allowed in other hand in analog clock we have 1 minute 30 second that is why it is called analog clock because here every values within a given limit this is a basic point between analog and digital signal. now lets move to temperature graph with time suppose first point of graph is first day of month and last point is last day of a month as we analyse the graph this is analog graph because on the graph each and every value is possible like 27.3⁰C, 27.7⁰C, 27.88⁰C and many more hence we have allowed any value from 0⁰C to Tmax so this is analog because it can take any values within the given limit so it is called analog signal. now in electronics Tmax is change to Vmax hence 0 to Vmax here V is voltage suppose Vmax = 20V hence 0 to 20V it can take any value so it is an analog signal now lets move to different type of signal which is called discrete signal. Discrete time signal : it is important to understand before move to digital signal so lets start the signal which is defined for the discrete intervals of time see picture below.
discrete the time axis discretise means we are measuring the temperature every day 11 am that is t0 is first day, t1 is second day, t2 is third day and so on the last day and all are on 11 am hence what is temperature between 11 am of first day and 11 am of second day we don’t know so this is how a discrete signal looks like above picture so we have the value of function temperature at f(t0), f(t1), f(t2), f(t3) ….f(tn ) but what is value between f(t0) and f(t1) we don’t know because we have not monitored the function temperature value at that particular time so this is what a discrete signal looks but you should know one point the signal is actually analog if we chain or join the discrete signal it is actually analog signal hence discrete signal is subset of analog signal so this is important point to know and all real signal are analog signal. Digital Signal : in digital signal we discrete both time and magnitude we divide the magnitude axis into the fixed number of levels and the signal can take value equal to there levels only as above shown in figure. T(t1) = 9⁰ T(t4) = 15⁰ (discrete time signal ) T(t2) = 38⁰ T(t5) = 45⁰ T(t3) =24⁰ ∆t = t1t0 = t2t1 =t3t2 …….. now magnitude discrete levels as 0,15,30,45 signals can take only these value now we will analyse digital signal consider T(t1) is 9⁰ C but in the digital signal 9 is not allowed only magnitude value level is 0⁰ or 15⁰ so what value should consider logically 9⁰ C is near to 15⁰ C but wait in digital signal we always consider lower level value because to minimize error this is key point remember we select lower value not higher value hence at T(t1) digital value will be 0⁰ C so T(t1) = 0⁰ C T(t2) = 30⁰ C ( Lower value only) T(t3) = 15⁰ C T(t4) = 15⁰ C ( it is allowed ) T(t5) = 45⁰ C ( it is allowed ) note where value is not allowed other than digital level in that case select always lower value to minimize error above are values in case of digital signal so you can clearly seen the discrete time signal value and digital signal value Discrete time signal 
T(t2) = 38⁰ T(t5) = 45⁰ T(t3) =24⁰ Digital signal T(t1) = 0⁰ C T(t2) = 30⁰ C ( Lower value only) T(t3) = 15⁰ C T(t4) = 15⁰ C ( it is allowed ) T(t5) = 45⁰ C ( it is allowed ) hence the most important point in discrete signal any value can take within the limit but in digital signal only allowed level value is consider and in case if allowed value is not matching then always take lower value in digital signal.
dated 29th Sep 2018 
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