 Hello everyone, Myself Deepali Vardhkar working as assistant professor, WIT Solapur. Welcome to this video lecture, today we will study Perl's amplitude modulation. At the end of this video lecture student will be able to illustrate working of PAM modulator with its waveform and also student will be able to illustrate working of PAMD modulator with its waveform. Classification of Perl's modulation. Perl's modulation classified into two types, analog Perl's modulation and digital Perl's modulation. Analog Perl's modulation is divided into three types depend upon which parameter of the carrier signal changes. So its types Perl's amplitude modulation, Perl's width modulation and Perl's position modulation. Next digital Perl's modulation its output is in the form of code that is in the form of digital signal 1 or 0. So it is divided into two types Perl's code modulation that is the PCM and delta modulation. Now Perl's amplitude modulation. In the Perl's amplitude modulation the modulating signal is a continuous time signal. Carrier signal is train of pulses whose amplitude and width is constant. These train of pulses are spaced from each other by time t s. It is called as a sampling period. So these train of pulses here act as a sampling function. In Perl's amplitude modulation the amplitude of these pulses varies according to the amplitude of continuous time signal. So depend upon how this amplitude varies there are two types that is the double polarity or it is also called as a bipolar PIM here positive as well as negative pulses present and second that is the unipolar. So only positive pulses present in a unipolar PIM. Now types of PIM there are two types of PIM natural PIM and flat top PIM. So first that is the natural PIM. In the natural Perl's amplitude modulated signal that at the starting of carrier pulse its amplitude is equal to instantaneous amplitude of continuous time signal and at the rest of this cycle it follows the amplitude of continuous time signal. So the top of all these pulses follows the natural shape of continuous time signal. So it is called as a natural PIM. Now the generation of natural PIM in this the continuous time signal x of t we can say it as a information signal or message signal. This continuous time signal is given to the low pass filter. Low pass filter is used to band limit this continuous time signal. Its frequency is cutoff frequency is adjusted to FM. So this low pass filter is used here to avoid the aliasing effect. Now the next block that is the multiplier here the another input to the multiplier that is the train of pulses it generate a train of pulses at constant interval. So this train of pulses having the constant amplitude constant width. This train of pulses based from each other by TS it is called as a sampling period and its frequency is a sampling frequency FS. This FS is always greater than twice of FM. The multiplier gives the output which is nothing but PIM where the amplitude of this pulses or this train of pulses varies according to the amplitude of continuous time signal. So the information which is contained here this information is in the amplitude variation of this train of pulses. So this is the circuit arrangement for natural PIM. Here the MOSFET used as a switch the continuous time signal x of t is given to this MOSFET the another signal to the MOSFET that is train of pulses it is called as a driving function C of t. We can see the PIM signal or output signal across the rear. So when driving function becomes on or goes to the higher value then this MOSFET act as a closed switch it turn on and it act as a closed switch. So at the output the amplitude of pulses is equal to instantaneous amplitude of continuous time signal. When the low value of this driving function is given to the gate of this MOSFET this MOSFET act as a open switch so the output at that time is a geo. So in this way we get a pulse amplitude modulated signal across the REL. Now the detection of this natural PIM. This natural PIM signal is passed through a low pass filter by using this low pass filter we can remove the high frequency repulse which are present in a PIM signal. The capacitor which is present in the low pass filter circuit it will charge during the on pulse and that capacitor will discharge during the off pulse. So in this way with the help of charging and discharging voltage of the capacitor the continuous time signal is obtained at the output of low pass filter. So the PIM signal is demodulated by using the low pass filter. Now next is a flat top PIM. In the flat top PIM at the starting of pulse the amplitude of this pulse is equal to instantaneous value of continuous time signal and for the rest of cycle this amplitude remains constant. So here the top of all these pulses remains flat or constant so it is called as a flat top PIM. It does not follow the natural amplitude of continuous time signal. Now this is the circuit arrangement for the flat top PIM. Here two feds act as a switch one is a sampling switch another is a discharging switch. A continuous time signal x of t is given to this switch pulse is given to the gate G1 at that time this sampling switch turns on and this capacitor starts charging. So these capacitors charges up to the point or up to the amplitude equal to amplitude of instantaneous value of continuous time signal. After this point sampling switch and discharge switch both switch becomes off and capacitor holds this voltage for one constant time period. You can say it as a tau. After at the end of this pulse the pulse is get applied to the G2 that is to the discharge switch. So this switch becomes on here sampling switch is off and due to this this capacitor will discharge to zero value. So in this way we get a flat top PIM signal at the output of this capacitor or across this capacitor. Now detection of flat top PIM here the PIM flat top PIM signal is applied to the reconstruction filter. This reconstruction filter is again low pass filter whose cutoff frequency is adjusted to FM or greater than FM. Now it will remove all the high frequency repulse from this PIM signal and the another circuit or another filter here use this is nothing but equalizer. So this equalizer is used to remove the aperture effect which is present in a flat top PIM signal. So what is this aperture effect in flat top PIM spectrum the high frequency component get attenuated due to one function or due to one transfer function. So this attenuation or this distortion in amplitude is called as aperture effect. So these distortions are removed by using one special filter it is called as a equalizer. Now this distortion less signal is obtained at the output of equalizer. So this is nothing but continuous time signal which is recovered from this PIM signal. Now next advantages of PIM it has better signal to noise ratio due to increased signal power all the circuits for PIM modulation as well as demodulations are simple so its generation and detection is easy. Now the question what is the effect of noise on PIM signal pause the video for a while and think. So this will comes in disadvantages of PIM signal. So as the information contained in the PIM signal is in the form of variation in amplitude and we know that noise effect is greater in amplitude of any signal. So there is a effect of noise on PIM which will distort the PIM signal. Also another disadvantages that is the aperture effect introduced in the PIM signal especially in a flat of PIM signal. Now the applications of PIM so number of Ethernet standards are the examples of PIM applications in particular 100 base T4 and broad arc reach it uses a 3 level PIM system then 1000 base T it use level 5 PIM system and 10 G base T use 16 level PIM system. This PIM concept is also used to study of photosynthesis by special instrument and it is comes in a photo biology. Next electronics divers for LED lightning the PIM system is used or developed to control the light emitting diode especially for lightning application. Next in digital television the North American advanced television system committee standards for digital television use a form of PIM to broadcast a data which generates a television signal. So these are the references. Thank you.