Pdf analog,digital and pulse modulation techniques researchgate. The first transmission of a message using pcm was in 1943 during the world war ii. Calculate the pulse width of each bit to support the multiplex of these 20 signals. Pulse width modulation traditional solenoid driver electronics rely on linear control, which is the application of a constant voltage across a resistance to produce an output current that is directly proportional to the voltage. A familiar example of pdm is the international morse code, used in shiptoshore communications, amateur radio, and certain other forms of radiotelegraphy. Pulse width modulation using digital pulses to create some analog value other than just high and low signal levels. Modulation techniques pwm and pulse code modulation. The time that the pulse be it long or short is high is the pulse width and the duty cycle, as we know, is the percentage of the pulse width as part of the pwm signals period. Pulsebased modulation for vlc systems tu delft repositories. Pulse code modulation pcm was pioneered by the british engineer alec reeves in 1937. If the negative symbol is transmitted, the pdf for z will be as sketched below. If noise enters into a system, it persists and gets carried up to the end receiver. The signal is modulated as a series of pulses at a high frequency, which can be demodulated as a pulse.
With the exception of some resonant converters, the vast majority of power electronic circuits are controlled by pwm signals of various forms. Pulse modulation definition of pulse modulation by the free. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. The actual number is represented by the position in time where the pulse appears in a given time slot. Pulse position modulation ppm a pulse of fixed width and amplitude is used to transmit the information. 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. Modulation is the process of changing the characteristics of the carrier signal in accordance with the instantaneous values of the modulating signal message signal. Introducing pulse width modulation pwm the period is normally kept constant, and the pulse width, or on time is varied the duty cycle is the proportion of time that the pulse is zon or high, and is expressed as a percentage. Types of modulation 6 flynnkatz 7810 analog modulation amplitude modulation, am frequency modulation, fm double and single sideband, dsb and ssb digital modulation phase shift keying. Therefore, analog modulation includes am, fm and pm and these are more sensitive to noise. 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. Jan 15, 2018 modulation is the process of changing the characteristics of the carrier signal in accordance with the instantaneous values of the modulating signal message signal. 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. Onoff pulse before and after 20 db sideband reduction with a series emitter negative group delay filter.
Pulse amplitude modulation an overview sciencedirect. Emphasis is placed on explaining the tradeoffs that are made to optimize efficiencies in. The amplitude of the analog signal is sampled at uniform intervals and each sample is quantized to its nearest. Another kind of pulse modulation is pulse duration modulation pdm, in which intelligence is represented by the length and order of regularly recurring pulses. It is customary to arrange the points so that they are equally spaced and centered at zero. 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. Pulsewidth modulation the output of a pwm amplifier is either zero or tied to the supply voltage, holding losses to a minimum. In pulse width modulation or pulse duration modulation, the width of the pulse carrier is varied in accordance with the sample values of message. In pam the amplitude of the individual pulses are varied according to the amplitude of the modulating signals. We will assume that all message signals mt from now on are sampled above the. The theoretically zero rise and fall time of an ideal pwm waveform represents a preferred way of driving modern semiconductor power devices. 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.
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. In pulse width modulation or pulse duration modulation, the width of the pulse carrier is varied in accordance with the sample values of message signal or modulating signal or modulating voltage. Pulse modulation communications university of toronto. Pulse modulation has another outstanding advantage.
Pdf chapter 2 pulsewidth modulation semantic scholar. Pulse width modulation and in position ppm, pulse position. The width of the pulse varies in this method, but the amplitude of the signal remains constant. Pulse position modulated ppm ground receiver design for. A technique by which analog signal gets converted into digital form in order to have signal transmission through a digital network is known as pulse code modulation. Pulsewidth modulation pwm, or pulseduration modulation pdm, is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts.
Reduced distortion and improvement in signal to noise ratios. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The pam modulator and demodulator circuits simple compared to other kind of modulation and. The modulation techniques used to convert analog signal into digital signal are a pulse code modulation b delta modulation c adaptive delta modulation d all of the above view answer hide answer. The modulation processisprobablyeasier tounderstand whenviewed fromthe perspective of amplitude modulation. Pulse width modulation has changed the world by slashing the power consumption of appliances utilizing motors such as inverter air conditioners pdf, inverter refrigerators, inverter washing machines, among many others.
Investigation of the pulse time modulation techniques for. It is basically signal coders also known as waveform coders. 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. In pulse width modulation pwm or pulse duration modulation pdm or pulse time modulation ptm technique, the width or the duration or the time of the pulse carrier varies, which is proportional to the instantaneous amplitude of the message signal. For example, inverter air conditioners can consume less than half the energy that their noninverter counterparts do in some. All pulse modulation systems boil down to two basic principles. Pulse frequency modulation is somewhat similar to ordinary fm, except that the basic carrier consists of equally spaced pulses rather than a sine wave.
Pdf download pulse width modulation for power converters. So, this drawback can be overcome by the digital modulation technique. A system of modulation in which pulses are altered and controlled in order to represent the message. Digital modulation in communications systems an introduction. No information is lost, but the energy is redistributed in the frequency domain. We use modulation technique to alter signals in time and frequency to accomplish desired objectives. It is the standard form of digital audio in computers, cds, digital telephony and other digital audio applications. A familiar example of pdm is the international morse code, used in ship to shore communications, amateur radio, and certain other forms of radiotelegraphy.
Pulse coded modulation pcm is a form of modulation where there is no carrier, so that makes it a pure digital system. Pam underlies the operation of a wide variety of modems. Pulse width modulation the output of a pwm amplifier is either zero or tied to the supply voltage, holding losses to a minimum. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. Of them all, the digital modulation technique used is pulse code modulation pcm.
Analog and digital pulse modulation techniques need. It can be one of your morning readings pulse width modulation for power converters. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. There are many modulation techniques, which are classified according to the type of modulation employed. The move to digital modulation provides more information capacity, compatibility with digital data services, higher data security, better quality communications, and quicker system availability. Many many digital systems are powered by a 5volt power supply, so if you filter a signal that has a 50% duty cycle you get an average. These are currently used in every cell phone and digital radio today. Pulse modulation, october 1960 popular electronics rf cafe. 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.
A signal is pulse code modulated to convert its analog information into a binary sequence, i. As the duty cycle changes to deliver more or less power, efficiency remains essentially constant. The output of a pcm will resemble a binary sequence. 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. In pulse amplitude modulation pam, the a m are purely real, that is im a m 0 for m 1, 2, m. Pulse code modulation and time division multiplexing. Pulse modulation is a type of modulation where some parameter of. It uses transmitter energy more efficiently than either am or fm because of the simple onoff nature of the pulses. However, this conclusion leaves the possiblity that dis tortions which are insigni. As mentioned above, ppm modulation consists of mapping each sequence of l databits into one of m 2l slotlocations according to a predetermined lookup table, and firing the laser so as to place the optical pulse in the correct slot relative to the previous pulse.
Ifwesmooth the baseband pulse edges, we should be able to reducethe bandwidthof the pulse. This means that a pulse transmitter will have a longer range than an am transmitter of the same power. It is the extent of modulation denoted in percentage, and is denoted by m. The original waveform amplitude is quantized with a resulting loss of information. Pulse amplitude modulation pam theory of and its applications. For the baseband digital transmission, pulse amplitude modulation pam is the most efficient in terms of power and bandwidth utilization. Another kind of pulse modulation is pulseduration modulation pdm, in which intelligence is represented by the length and order of regularly recurring pulses.
Here we will discuss in details, pulse modulation and pulse modulation techniques like pulse amplitude modulation pam, pulse width modulation pwm, pulse position modulation ppm and pulse code. Lipo this is a soft file publication that can be got by downloading from on the internet book. Pulsewidthmodulation control circuits slvs084f april 1994 revised january 2002 post office box 655303 dallas, texas 75265 1 complete pwm power control 3. Feedback can be used to achieve an output that matches exactly the control signal. This video lecture describes, pulse width modulation pwm concept and related theory. Pdf differential pulse code modulation differential. In general, the larger the command signal, the wider the pulse. Many signals in modern communication systems are digital also, analog signals are transmitted digitally.
Pulse modulation definition of pulse modulation by the. Developers of communications systems face these constraints. Pulse duration modulation pdm or pulse width modulation pwm. This reduces to the very simple sigmadelta modulation, more detailed models of the vocal tract further reduce the amount of data needed by vocoders to transmit. Pulse modulation demodulation of pam signals method 1. For a better quality and efficient communication, digital modulation technique. Analog communication pulse modulation tutorialspoint. Consequently, the constellation points lie on the horizontal line.
Problem 3 consider n signals, each bl 1 hz and is quantized to 16 levels. For a perfect modulation, the value of modulation index should be 1, which means the modulation depth should be 100%. Because pwm turns the coils of the motor it drives on and off, the motor itself will often vibrate at the speed of the pulse width 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.
Pulsewidth modulation pwm is the basis for control in power electronics. 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. Pulse amplitude modulation pam, quadrature amplitude modulation qam 12. Pulse code modulation modulation is the process of varying one or more parameters of a carrier signal in accordance with the instantaneous values of the message signal. Pulse code modulation is the heart of technology in communications in todays. Sampling theorem determines the necessary conditions which allow us to change an analog signal to a discrete one. Pulse amplitude modulation an overview sciencedirect topics. Pulse number modulation pnm related to ppm in the sense that we are using pulses with fixed amplitude and width. Next topic pulse code modulation pulsecode modulation pcm is used to digitally represent sampled analog signals. Jul 01, 2019 since pulse width modulation requires relatively simple circuitry, it is the ideal type of pulse modulation for use in outer space vehicles. Modulation is the process by which we map information on to a carrier. Pdf differential pulse code modulation differential pulse. In cw modulation schemes some parameter of modulated wave varies.
Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. We expect a rectangular pulse to have a very broad frequency spectrum, due to the sharptransitions atthe pulse edges. Modulation is broadly classified into two categories namely analog modulation a. The pulse may take any real voltage value that is proportional to the value of the original waveform. The longer the switch is on compared to the off periods. The following figures explain the pulse amplitude modulation. Pdf introduction to various signal modulation techniques to have effective transmission of signals and comparison among them find, read and cite all the. The carrier frequency, fc, should be larger than the highest spectral component. Oct 03, 2011 this is a ppt for pulse modulation for final year ej diploma. Sampling theorem and pulse amplitude modulation pam. The first version, the transmission system 1 t1, was introduced in 1962 in the bell system, and could transmit up to 24 telephone calls simultaneously over a single transmission line consisting of copper wire.
170 1365 1502 889 539 1190 566 666 783 133 430 132 158 1408 1573 918 16 786 1338 1618 70 902 1366 90 1114 702 1313 671 921 1214