Demodulation of pulse amplitude modulation pam for the love of physics walter lewin may 16, 2011 duration. Pulse amplitude demodulation peak detection is used to detect pam. In analog modulation technique, if the amplitude, duration or position of a pulse is varied in accordance with the instantaneous values of the baseband modulating signal, then such a technique is called as pulse amplitude modulation pam or pulse durationwidth modulation pdmpwm, or pulse position modulation ppm. Amplitude modulation is defined as the process in which the amplitude of the carrier wave ct is varied about a mean value, linearly with the baseband signal. Sampling theorem and pulse amplitude modulation pam. Seeing a little of the theory and mathematics behind amplitude modulation gives a better understanding of how it works. It is another type of ptm, where the amplitude and width of the pulses are kept constant and only the position of the pulses is varied. Pulse code modulation is a method that is used to convert an analog signal into a digital signal, so that modified analog signal can be transmitted through the digital communication network. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. The pulse amplitude modulated signal, will follow the amplitude of the original signal, as the signal traces out the path of the whole wave. A demodulator is an electronic circuit or computer program in a softwaredefined radio that is used to recover the information content from the modulated carrier wave. Pulse amplitude modulation pam pam modulation youtube. In amplitude modulation theory, the amplitude of a carrier signal is varied by the modulating voltage, whose frequency is invariably lower than that of the carrier. In this chapter we will discuss ways of demodulating am, cw, fm, phase, and pulse modulation.
Introduction to modulation and demodulation modulation. Amplitude modulation am refers to the modulation technique where the carriers amplitude is varied in accordance to the instantaneous value of the modulating or baseband signals amplitude. In pam the amplitude of the message or modulating signal is mapped to a series of pulses with two possible. Pulse amplitude modulation is defined as the data transmission by altering the amplitudes power levels or voltage of every pulse in a regular time sequence of. The theory and equations show that furthest extent of the sidebands from the carrier corresponds to the highest frequency of the modulating tone for the amplitude modulated signal.
In both the modulation and demodulation, it is assumed that the bandwidth of. Although an inductive type transformation process is required, the output dc may be obtained without rectifying devices. Radio waves can carry audio, video, and digital information over great distances by using changes in a carrier waves amplitude, frequency, or phase to represent the information being transmitted. Demodulation is the process by which the original information bearing signal, i. Figure 321 includes a simplified circuit view a for this demodulator and its waveforms views b and c. There are many types of modulation so there are many. Pulse amplitude demodulation theory working of circuit. In this video you will learn the block diagram of pwm and ppm. In pam the amplitude of the message or modulating signal is mapped to a series of pulses with two possible variant. In pulse amplitude modulation pam, the a m are purely real, that is im a m 0 for m 1, 2, m.
It is customary to arrange the points so that they are equally spaced and centered at zero. Each channel sharing scheme a set of basis vectors. Fig2 shows the spectrum of pulse amplitude modulated signal along with the message signal and the sampling signal which is the carrier train of pulses with the help of the waveform plotted in time domain. The process of demodulation for signals using amplitude modulation can be achieved in a number of different techniques, each of which has its own advantage. Pulse width modulation pwm, or pulse duration modulation pdm, is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. Oct 14, 2018 this video is about the demodulation detection of pulse width modulation pwm and pulse position modulation ppm. In the positive half cycle of pam signal, diode conducts and current flows through r, whereas in negative half cycle, the diode is reversed biased and. The output of a sampling circuit with a zeroorder hold zoh is one example of a pam signal. Consequently, the constellation points lie on the horizontal line. Pulse modulation demodulation of pam signals method 1. Principles of communication modulation tutorialspoint. An am wave may thus be dscribed, in the most general form, as a function of time as follows. A modem is an equipment that performs both modulation and demodulation. Pulse amplitude modulation circuit, definition, advantages.
Pulse amplitude modulation is a analog pulse modulation technique. There are two types of pulse amplitude modulation based on signal polarity 1. Modulation is the process of influencing data information on the carrier, while demodulation is the recovery of original information at the distant end from the carrier. The modulation index can be used to make the carrier amplitude more or less sensitive to the variations in the value of the baseband signal. Single sideband amplitude modulation one method to produce signal sideband ssb amplitude modulation is to produce dsbam, and pass the dsbam signal through a band pass filter, usually called a single sideband filter, which passes one of the sidebands as illustrated in the diagram below. May 24, 2017 this lecture explains basics of pulse amplitude modulation pam and pam waveform. Cr1 is the input diode which allows capacitor c1 to charge to the peak value of the pam input pulse. Pulse amplitude modulation pam is defined as the data transmission by altering the amplitudes of every pulse in a regular time sequence of electromagnetic pulses. Pulse amplitude modulation circuit, definition, advantages, types. In the case of analog pulse amplitude modulation signals, the number of pulse amplitudes can be infinite.
It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. Pulse amplitude modulation theory pulse amplitude modulation. The pam signal can be demodulated by means of a low pass filter which passes. Pulse amplitude modulation an overview sciencedirect topics.
It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal. Pulse amplitude modulation pam is one of several forms of single modulation in which data is transmitted through varying the amplitude of the pulses in regular timed sequence of electrical or electromagnetic pulses. The average value of voltage and current fed to the load is controlled by turning the switch between supply and load on and off at a fast rate. Amplitude modulation corresponds to multiplying the carrier by the shifted baseband signal. In practice, the carrier may be highfrequency hf while the modulation is audio. Transmitter and receiver circuits are simple and easy to construct. Sampling theorem determines the necessary conditions which allow us to change an analog signal to a discrete one.
The process of retrieval of information from the carrier wave at the receiver is termed demodulation. Pwm converts an audio signal into a sequence of pulses having constant amplitude, but the width is proportional to amplitude of an audio signal. Explain generation and demodulation of pam, ppm and pwm with. Both processes aim to achieve transfer information with the minimum distortion, minimum loss and. Pulse amplitude modulation pam, quadrature amplitude modulation qam 12. Pam is the simplest of all pulse modulation technique. Pcm is in binary form,so there will be only two possible states high and low 0 and 1. Pulse amplitude modulation pam, quadrature amplitude modulation qam. Synchronous modulation and demodulation low dc current may be transformed into a high voltage dc by simple chopper action. The probability of error of all the digital modulation and demodulation schemes based on the. The demodulator is composed of a lowpass filter, whose.
For the baseband digital transmission, pulse amplitude modulation pam is the most. Pcm is in binary form,so there will be only two possible states high and low0 and 1. Pulse amplitude demodulation september 4, 20 by ashutosh bhatt the simple pulse modulation technique called pulse amplitude modulation pam proved to be more power efficient than the pwm and consumes constant power for individual pulses like ppm. Pulse modulation may be used to transmitting analog information, such as continuous speech signal or data. Aug 20, 2017 synchronous modulation and demodulation. The circuit in which restoration is achieved is called the detector or demodulator both of these terms are used in neets. Double polarity pulse amplitude modulation in single polarity pulse amplitude modulation, there is fixed level of dc bias added to the message signal or modulating signal, so the output of modulating signal is always. Pulse amplitude modulation pam is an analog modulating scheme in which the amplitude of the pulse carrier varies proportional to the instantaneous amplitude of the message signal. Pulse amplitude modulation pam theory of and its applications. Hence, pam is continuous in amplitude but discrete in time. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. Pulse modulation and demodulation sampling theory using matlab duration. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. Demodulation is extracting the original informationbearing signal from a carrier wave.
A modulation technique that allows variation in the position of the pulses according to the amplitude of the sampled modulating signal is known as pulse position modulation ppm. Pammodulationanddemodulation mini projects electronics. Pulseamplitude modulation is the simplest form of signal modulation and analog to digital conversion method where the message information is. Amplitude modulation theory frequency spectrum power. To understand the theoretical foundations of analog communications as well as of doublesideband amplitude modulation and demodulation dsbam to design the simulink model of the dsbam to analyze each signal in time and frequency domains using time scope and spectrum analyzer. It is a simple process for both modulation and demodulation.
Pulse position demodulation october 12, 20 by ashutosh bhatt the pulse position modulation ppm is a modulation technique designed to achieve the goals like simple transmitter and receiver circuitry, noise performance, constant bandwidth and the power efficiency and constant transmitter power. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. If we were to implement every possible combination of demodulation algorithm, carrierrecovery technique, and clock regeneration as a distinct model, the combinatorial explosion of different models would become unmanageable. We can also get back our analog signal by demodulation. In the frequency domain, amplitude modulation corresponds to translating the baseband spectrum to a band. Synchronous modulation and demodulation photo optical modulator. Pulse amplitude modulation pam is an analog modulating scheme in which the amplitude of the pulse carrier varies proportional to the instantaneous amplitude. Demodulation of pwm and ppm block diagram and waveform. The goal of this experiment is to become familiar with fm modulation and demodulation. Pulse amplitude modulation pam the actual amplitude of the pulse represents the number being transmitted. Pulse amplitude modulation pam, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the signal at the instant of sampling. Pulseamplitude modulation pam, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i.