 Hello everyone. Welcome to this video lecture. Myself Deepali Vardhakar working as assistant professor at WIT Solapur. Today we will study the pulse position modulation. At the end of this video lecture, student will be able to illustrate working of PPM modulator and demodulator with its waveforms. Student will be able to compare PAM, PWM and PPM. These are the contents. First introduction to PPM, PPM modulator, PPM demodulator, advantages and disadvantages of PPM, applications, then comparison between PAM, PWM and PPM. Now what is PPM? It is pulse position modulation. Here the amplitude and width of the pulses remains same, but the position of the pulses changes according to the amplitude of continuous time signal. So, the distance between each pulse is different and this distance is depend upon the amplitude of modulating signal. Next PPM generator, here the comparator circuit to the non-inverting terminal of this comparator modulating signal that is the continuous time X of t signal is applied. To the inverting terminal of this comparator, sawtooth generator or sawtooth wave is applied. Next the modostable multivibrator is used after the comparator circuit. Let us see working of both this circuit. First is a comparator. Here to the input of comparator continuous time signal X of t which is at the non-inverting terminal and sawtooth wave which is at the inverting terminal. The comparator gives output high when the falling edge of RAM signal and the output of comparator remains high as long as the continuous time signal X of t is greater than RAM signal. So, at this point where the continuous time signal and RAM signal coincide with each other, the comparator output becomes low. So, in this way the variable width pulses of 10 at the output of this comparator. So, the width of pulses is depend upon change in amplitude of continuous time signal. So, in this way the PWM signal is obtained at the output of comparator. This PWM signal applied to the monostable multivibrator. Let us see the working of this monostable multivibrator. This monostable multivibrator is negative edge triggered. So, this PWM signal is applied to the monostable multivibrator as the trailing edge or falling edge of PWM signal is applied to the monostable multivibrator. So, this trailing edge act as a negative edge triggered to the monostable multivibrator. The monostable multivibrator gives the output high after this trailing edge and this output high remains high for a constant time period. So, this time period is decided by its own RC component. So, when the trailing edge of PWM signal comes at that time the monostable multivibrator output goes to the high. So, in this way as the trailing edge comes the monostable output goes to the high. So, the variable position pulses often at the output of monostable multivibrator. So, in this way we get a PPM output at the monostable multivibrator output. Now, next is a PPM demodulator. The PPM pulses are applied to the pulse generator. Same PPM pulses also applied to the reference pulse generator. So, both inputs are given to the SR flip-flop. The SR flip-flop output is given to the PWM demodulator and at the output is modulating signal. Now, let us see working of each block. So, here the SR flip-flop to that the PPM signal that is the pulse generator output is applied to the reset pin of SR flip-flop and reference pulse generator its output is applied to the set pin of this SR flip-flop. As this SR flip-flop is positive edge triggered when the clock pulse is applied that is the reference pulse output is applied to the set pin of the SR flip-flop. At that time it set the SR flip-flop means the output becomes high. And when the positive edge trigger that is the reference pulse its positive edge trigger is applied to the reset pin of this SR flip-flop it will reset this flip-flop means output becomes low. So, in this way with the help of set and reset pin the SR flip-flop output becomes high and low. So, if we see the output at the SR flip-flop we get a variable with the pulses and this is nothing but PWM signal. So, after the SR flip-flop we get a PWM signal that is the pulse width modulated signal. Now, this PWM signal is applied to the PWM demodulator circuit. So, already we have studied this PWM demodulator circuit in the previous lecture. So, with the help of all these blocks we get a continuous time signal or analog signal at the output of PWM demodulator. Now, the question what will the effect of noise on PPM? So, this will come in advantages of PPM as the PPM consists constant amplitude pulses. So, the effect of noise is very less on the PPM. So, noise interference is less it is easy to separate out signal from noisy signal. So, PPM signal can be easily reconstructed with noise-contaminated PPM. Then the instantaneous power of PPM modulated signal remains constant because the PPM having constant width and constant amplitude. So, there is a no any change in power of pulses. It requires less power as compared to PAM due to short duration pulses. Next, disadvantages of PPM. So, here in PPM synchronization is required between the transmitter and receiver. The PPM is highly sensitive to multi-path way interference as there is a change in a position of the pulses. So, here the bandwidth required is large as compared to PAM. Then the application of PPM. The PPM is used in optical communication system. It is used in radio control, model aircraft and boats and cars. It is used for military applications. The position of each pulse may describes the physical direction of analog controller while the number of pulses may describes the number of possible commands that the device may receive the comparison of PAM, PWM and PPM. So, these are the parameters. First, that is variable parameter of pulsed carrier. In PAM the amplitude of pulses varies according to the continuous time signal. In PWM the width of pulses varies according to the amplitude of continuous time signal and in PPM the position of pulses varies according to the according to the continuous time signal. Next parameter that is the bandwidth requirement as the PAM having constantly varying amplitude. So, the bandwidth required for PAM is low. In PWM the width of pulses varies continuously. So, it requires high bandwidth. In PPM the position of pulses varies. So, it also requires higher bandwidth. Then transmitted power. The transmitted power varies with amplitude of pulses. Here as there is a variation in a width of pulses. So, the transmitted power is also variable. But in PPM the pulse amplitude and width of the pulses is same. So, the transmitted power remains constant. In PAM the information contained in the form of variation in amplitude, noise effect is large and it has a low noise immunity. In PWM the information contained in the width of the pulses. So, here no any variation in amplitude. So, less effect of noise. So, noise immunity for PWM is high. In PPM the amplitude of the all pulses remains same. So, very less effect of noise in on the PPM signal. So, it also has a higher noise immunity. So, these are the waveforms for PAM, PWM and PPM. These are the references. Thank you.