We use modulation technique to alter signals in time and frequency to accomplish desired objectives. The waveforms, definition and basic concepts of each digital modulation techniques are discussed here. Another basic concept in pulse modulation is the modulation itself. No information is lost, but the energy is redistributed in the frequency domain. This way pulse time modulation can be classified into three types. The second class of digital modulation format is called multilevel signaling formats. In pulse width modulation, there are different types of modulation for analog and digital as shown below. A pulsecode modulation pcm system, as shown in figure 5. A block diagram showing the basic classification of modulation techniques is given below. There are many modulation techniques, which are classified according to the type of modulation employed.
Null at 3 pam and pcm pam pulse amplitude modulation. Amplitude modulation early radio ee 442 spring semester. All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. Modulation modulation is the process whereby some characteristic of one wave is v aried in accordance with some characteristic of another wave. There are three types of pulse width modulation pwm. Pulse code modulation an overview sciencedirect topics. Pdf generation of pulse width modulation pwm signals. Modulationtypesamplitude,frequency,phase modulation. Of them all, the digital modulation technique used is pulse code modulation pcm. There are several types of modulation according to the nature. The tail edge can be fixed and the lead edge modulated. Demodulation is the opposite process of modulation.
Our study begins with the pulseamplitude modulation pam scheme. Pulse amplitude modulation pulse code modulation sampling. The output of a pcm will resemble a binary sequence. There are two types of modulation analog and digital. So now lets discuss different types of pulse modulation techniques in detailpulse modulation can be categorized broadly into two types. Pulse amplitude modulation is categorized into two types. Modulation techniques pwm and pulse code modulation.
Figure 2 pulse before pwm figure 3 pulse after pwm 3. Sampling is common in all pulse modulation techniques. It is a type of pulse time modulation ptm technique where the timing of the carrier pulse is varied according to the modulating signal in pulse duration modulation pdm, the amplitude of the pulse is kept constant and only the variation in width is noticed. In this chapter, let us discuss the following analog pulse modulation techniques.
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 digital modulation is also used in both analog and digital communications. The basic types of modulation are angular mo dulation including the special cases of phase and frequency modulation and amplitude modulation. The following safety and common symbols may be used in this manual and on. It is designed for highfrequency operation and has a low. Where as digital modulations are with bit streams or symbols from computing vevices as base band signals. Modulation is broadly classified into two categories namely analog modulation a. Modulation, analog modulation, digital modulation, am,fm. Lets us look at some of the different types of pulse modulation. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. The baud or signalling rate defines the number of symbols per. In these formats, the message waveforms are linecodes with symbols representing multiple bits. Ap1609710 different pwm for three phase acim 060803 for. The analog pulse modulation is again classified as, 1.
Pulse amplitude modulation an overview sciencedirect. Pulse amplitude modulation has some applications, but it is not used by itself in data communication. Pulse code modulation is a method that is used to convert an analog signal into a digital signal so that a modified analog signal can be transmitted through the digital communication network. Analog communication pdf notes book starts with the topics covering introduction ac, dsb modulation, ssb modulation, angle modulation concepts, angle modulation methods, noise etc. For a better quality and efficient communication, digital modulation technique. The pulse amplitude modulation is the modulation of signals by. In continuous wave modulation amplitude modulation, frequency modulation, phase modulation the carrier wave used is continuous in nature, while in case of pulse modulation, the carrier wave is in the form of pulses. In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. The pulse center may be fixed in the center of the time window and both edges of the pulse moved to compress or expand the width. Or the process of modulation can be defined as varying the rf carrier wave in accordance with the intelligence or information in a low frequency signal. This choice of key determines the scale you use, how many sharps and flats there are and what chords you can use.
Basic pulse width modulation pwm tutorials of cytron. Pulse position modulation ppm is an analog modulation scheme in which, the amplitude and the width of the pulses are kept constant, while the position of each pulse, with reference to the position of a reference pulse varies according to the instantaneous sampled value of the message signal. Pulse amplitude modulation pulse width modulation pulse position modulation pulse code modulation pulse modulation the process of transmitting signals in the form of pulses discontinuous signals by using special techniques. If noise enters into a system, it persists and gets carried up to the end receiver. For bpsk this is just a rectangular pulse of duration t. Pulse modulation communications university of toronto. Here you can download the free lecture notes of analog communication system pdf notes ac notes pdf materials with multiple file links to download. Double polarity pam is a situation where the pulses are both positive and negative. When we take the pulse digital modulation, we use a periodic sequence of rectangular pulses as the carrier signal. Another way of expressing the modulation index is in terms of the maximum and minimum values of the amplitude of the modulated carrier wave. Analog modulation delas with the voice, video and regular waves of base band signals. Pulse modulation, october 1960 popular electronics rf cafe. Sampling theorem determines the necessary conditions which allow us to change an analog signal to a discrete one. These three types are shown in the above given figure, with timing slots.
Pulse amplitude modulation is the basic form of pulse modulation. Modulation describes the process where a piece of music changes from one key to another key when you start writing a piece of music one of the first things you do is choose a key to compose in. When we modulate a carrier wave, we ordinarily alter its amplitude am, its frequency fm, or its phase pm. In this modulation, the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the modulating signal. The pulse may take any real voltage value that is proportional to the value of the original waveform. The nice thing about a pulse is that theres another. Output frequency and voltage is controlled electronically by controlling the width of the pulses of voltage to the motor. So, this drawback can be overcome by the digital modulation technique. All about modulation basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. The lead edge can be held at the lead edge of the window and the tail edge modulated.
Modulation for frequency assignment the fcc assigns frequency bands to each radio application. In this article we will see an introduction of pulse width modulation. Sampling theorem and pulse amplitude modulation pam. Single polarity pam is a situation where a suitable fixed dc bias is added to the signal to ensure that all the pulses are positive. Analog communication pulse modulation after continuous wave modulation, the next division is pulse modulation. Pulse width modulated pwm drives rockwell automation. Pcm is the preferred method of communication within the public switched telephone network pstn. Modulation is the process of changing the characteristics of the carrier signal in accordance with the instantaneous values of the modulating signal message signal. The impulse response is h t pt t the output of the low pass. For the baseband digital transmission, pulse amplitude modulation pam is the most efficient in terms of power and bandwidth utilization. Pulse modulation definition, types, block diagrams, pulse. Or modulation is defined as the precess by which some characteristics, usually amplitude, frequency or phase, of a carrier is varied in. Pcm is in binary form, so there will be only two possible states high and low0 and 1. Analog communication pulse modulation tutorialspoint.
Channels, modulation, and demodulation of binary pam where the basic pulse shape pt is a sinc function. Pulse width modulation the most popular power devices for motor control applications are power mosfets and igbts. Its main features can be summarized as sinetriangle wave comparison. Pulse code modulation is a technique, which is used to convert an analog signal into digital signal. Pdf analog communication system pdf notes ac notes sw. A brief discussion about pulse code modulation and. We can also get back our analog signal by demodulation. Percentage modulation, %m m100 v m v c 100 the percentage modulation lies between 0 and 80%. This sampled variable amplitude pulse is then digitalized by the analog to digital converter. What is different in ppm is that ppm uses pulse positions to carry information. This video discusses digital modulation techniques ask, fsk and psk. The bit rate defines the rate at which information is passed. Pulseamplitude modulation pam, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. Before we study in detail about pam lets know the concepts of modulation.
Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Modulation for ease of radiation antennas must be greater than onetenth of the wavelength 10. In the intermediate dc circuit, the dc voltage is filtered in a lc lowpass filter. However, it is the first step in another very popular conversion method called pulse code modulation. Pulse width modulation has many application in digital communication, power electronics, auto intensity control of street lights, speed control of dc motor and variable pwm to generate analog signal from digital signals, digital to analog converter. Analog and digital pulse modulation techniques gate study. Therefore, analog modulation includes am, fm and pm and these are more sensitive to noise. The analog modulation techniques are mainly classified into pulse amplitude. Most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast a modulator is a device that performs modulation. The input sequence b k consists of binary digits bits 1 and 0 with a bit duration of t b and a bit rate of r b 1 t b. Modulation is the process of superimposing a low frequency signal on a high frequency carrier signal. The pulse code modulator technique samples the input signal xt at a sampling frequency. In this type of drive, a diode bridge rectifier provides the intermediate dc circuit voltage. A signal is pulse code modulated to convert its analog information into a binary sequence, i.
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