 Hello everyone. Welcome to this video lecture. Myself Dipali Vardhakar working as assistant professor at WIT, Solarpur. Today we will study the pulse width modulation. At the end of this video lecture, student will be able to illustrate working of PWM modulator and demodulator with its waveform. Student will be able to illustrate the application of PWM. These are the content introduction to PWM, PWM modulator, PWM demodulator, advantages and disadvantages of PWM, then application of PWM. Now the pulse width modulation, it is the technique for delivering partial power to the load through digital means. So, this is the one of the example how this pulse width modulation will transmit a partial power to the load. So, what is the pulse width modulation? In the pulse width modulation, the continuous time signal or message signal is suppose X of t, the carrier pulses is train of pulses. In PWM, the width of this carrier signal changes according to the amplitude of continuous time signal. Here, the amplitude of all pulses remains same. So, the information in the PWM is in the form of change of width of pulses. Next is a duty cycle. In PWM, how long a rectangular pulse stays on within a constant period is determined by the value of information signal. So, duty cycle is measured in percentage. So, what is the duty cycle? Suppose this clock pulse having total time period t and it remains on for this time period. So, its duty cycle is nothing but on time upon total time and percentage duty cycle is equal to on time upon total time period into 100. Next is a PWM generator. The PWM generator consists a comparator circuit. The analog signal is applied to the non-inverting terminal of this comparator and the sawtooth wave is applied to the inverting terminal of the comparator. Here, this sawtooth wave act as a sampling function and its frequency is fs. So, this frequency fs is always greater than the frequency of continuous time signal x of t. Now, this comparator gives output high as long as this continuous time signal remains higher than this RAM signal. Let us see the working of this comparator. The comparator gives the output high at the falling edge of this RAM signal and this output remains high up to the point where the continuous time signal and RAM signal coincide with each other. So, after this point the comparator output becomes low. So, in this way the starting edge of this PWM is decided by the falling edge of this RAM signal which are as fixed interval of time and the ending edge of this PWM is decided by the continuous time signal and the point at which the continuous time signal and RAM signal coincide with each other. So, see here again at this point this when the falling edge of RAM signal comes comparator output becomes high and then this output remains high up to the point where the continuous time signal is higher than this RAM signal and at this point the comparator output becomes low. So, in this way as the continuous time signal goes to the positive peak the width of this PWM signal is high as the continuous time signal goes to the negative side or negative peak the width of PWM signal is less. So, as the amplitude of this continuous time signal changes the width of PWM signal changes. So, in this way the PWM signal is obtained at the output of this comparator. Now, the demodulation of this PWM signal. So, first what is the demodulation? It is the act for extracting the original information bearing signal from modulated carrier wave. It is used to recover the information content from the modulated carrier signal. Now, let us see the PWM demodulator block diagram. So, this is the first PWM signal which is to be demodulated. This PWM signal is given to the RAMP generator. Same PWM signal is also given to the synchronous pulse generator. The output of RAMP's generator and synchronous pulse generator is given to the adder. Then this adder output is given to the clipper circuit and next the clipper circuit output is given to the low pass filter. Let us see one by one working of each block. Now, first PWM signal which is to be demodulated, this PWM signal having different width and its position and its amplitude is same. Next RAMP generator, PWM signal is given to the RAMP generator. This RAMP generator will generate a RAMP signal. The height of this RAMP signal is proportional to the width of this input PWM signal. So, at the end of this RAMP signal, the sample and hole circuit which is present inside this RAMP generator circuit, this will hold this amplitude and for the rest of this cycle. Next, synchronous pulse generator. So, the synchronous pulse generator will generate a train of pulses and these pulses having constant amplitude, constant width. But these pulses are synchronized with the leading edge of PWM. Then the RAMP generator output and synchronous pulse generator output given to the adder circuit. Then this adder will add this train of pulses or reference pulses with the RAMP signal and we get the output like this. RAMP signal and on that this reference pulse generator output. Now, this output of adder is given to the clipper circuit. Now, the question what is the function of clipper? Pause the video for a while and think. So, the clipper is a device which is used to remove or to limit some portion from the waveform at one particular level. So, it will remove some positive part or some negative part or maybe both the parts from the waveforms and remaining portion remains as it is. So, a tube biased clipper is used here which will clips off this part and gives the PAM at the output. Now, this PAM signal is passed through a low pass filter and it gives a continuous time signal X of t. So, in this way the continuous time signal X of t is recovered from a PWM signal. Now, next that is the advantages as the amplitude of a PWM signal is constant. So, effect of noise is less. So, it has good noise immunity. Here, the synchronization is not required between transmitter and receiver. It is easy to reconstruct the PWM signal from a noise-contaminated PWM signal. So, it is possible to separate out signal from a noise in case of PWM modulation. Next, in PWM the width of pulses varies. So, the power of this all the pulses also variable. So, the transmission system must be powerful enough to handle the variation in the width of pulses. The bandwidth required for the PWM communication is large as compared to pulse amplitude modulation system. Then applications, PWM system is used in a telecommunication. PWM is also used to control the speed of robots by controlling the motors. It is PWM is used to control the power which is delivered to the load without noise. So, it is used in RC devices. It is used in audio and amplification purpose. Also, it is used in video effects. The sum class of amplifiers use the PWM techniques. PWM also used in embedded application. It is also used in analog and digital applications. These are the references. Thank you.