When we take the pulse digital modulation, we use a periodic sequence of rectangular pulses as the carrier signal. Demodulation is the opposite process of modulation. Reduced distortion and improvement in signal to noise ratios. The output frequency is determined by this master oscillator. Pulse modulation communications university of toronto. Analog pulse modulation digital pulse modulation pulse amplitude pam pulse width pwm pulse position ppm pulse code pcm delta dm pulse modulation pulse amplitude modulation pam. In analog modulation, analog signal sinusoidal signal is used as a carrier signal that modulates the message signal or data signal. 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. 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. Some pulse modulation schemes also allow the narrowband analog signal to be transferred as a digital signal i.
For minimum distortion, the sampling rate should be more than twice the signal frequency. Investigation of the pulse time modulation techniques for. Analog communication pdf notes basic concepts, frequency modulation. The pulse may take any real voltage value that is proportional to the value of the original waveform. Ee4512 analog and digital communications chapter 6 the dsbsc am coherent receiver has a bandpass filter centered at f c and with a bandwidth of twice the bandwidth of st because of the lsb and usb. The general function sinusoidal waves is shown in the figure below, in which, three parameters can be altered to get modulation they are amplitude, frequency and phase. More precisely, we consider analog pam where we wish to. Most pwm systems do not allow for 0% or 100% modulation because the output would be dc and may damage other components in the signal path.
Pulse amplitude modulation an overview sciencedirect. Complete notes download link ac notes analog communication pdf free download unit i introduction. Analog and digital modulation refers to how a carrier signal is modified in order to transmit information. The am and fm radios are examples of analog data over analog medium. Chapter 6modulation techniques shandong university. Pulse position modulation ppm is an analog modulation scheme where, the amplitude and the width of the pulses are kept constant, while the position of each pulse, and also the reference to the position of a reference pulse varies according to the instantaneous sampled value of the message signal. Modulation, analog modulation, digital modulation, am,fm. In pulseamplitude modulation pam a pulse signal is used to sample an analog signal.
Frequency modulation the frequency of the carrier signal is proportional to the modulating. The first transmission of a message using pcm was in 1943 during the world war ii. Pwm is the poor mans digitalto analog converter dac. 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. Because the wider pulse has more time to integrate to a stable filter voltage and the smaller pulse has less time to disturb it. A single resistor, rset, programs the ltc6992s internal master oscillator frequency. 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. Where as digital modulations are with bit streams or symbols from computing vevices as base band signals. In general when we talk about a digital system, we are usually talking about digital information over an analog medium. Pulse width modulation pwm is a simple method of using a rectangular digital waveform to control an analog variable pwm control is used in a variety of applications, ranging from communications to automatic control 3. Pulse modulation accessscience from mcgrawhill education. It is analog to digital conversion method where the message information is encoded in the amplitude of the series of signal pulses. Digital modulation in somewhat similar to the analog modulation except base band signal is of discrete amplitude level.
Pdf introduction to various signal modulation techniques to have effective transmission of signals and comparison among them find, read and cite all the. Varying the amplitude, polarity, presence or absence, duration, or occurrence in time of the pulses gives rise to the four basic forms of pulse modulation. Our study begins with the pulseamplitude modulation pam scheme. However, it is the first step in another very popular conversion method called pulse code modulation. Sampling theorem determines the necessary conditions which allow us to change an analog signal to a discrete one. Calculate the pulse width of each bit to support the multiplex of these 20 signals. 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.
Although ptm has many advantages over analogue and. Pulse amplitude modulation pam pulse width modulation pwm pulse position modulation ppm analog overdigital methods. Modulation is broadly classified into two categories namely analog modulation a. Pulse amplitude modulation pam, quadrature amplitude modulation qam 12. Modulation techniques pwm and pulse code modulation. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. This analog pulse modulation schemes that i have just mentioned we have. In pulse modulation, the carrier is in the form of pulse rather than being a sine wave as in other types of modulation. Analog modulation delas with the voice, video and regular waves of base band signals. For the baseband digital transmission, pulse amplitude modulation pam is the most efficient in terms of power and bandwidth utilization. The same filter will do better on a low or high duty cycle pulse compared to a 50% duty cycle pulse. Pulse amplitude modulation is the basic form of pulse modulation. We will continue with our discussion on pulse modulation schemes, that we started last.
The radios are examples of analog data over analog medium. Common digital modulation techniques and pulse modulation. Sampling theorem and pulse amplitude modulation pam. Pulse code modulation pcm was pioneered by the british engineer alec reeves in 1937. Pulse amplitude modulation pulse code modulation sampling. Pulse position modulation ppm is an analog modulating scheme in which the amplitude and 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. The time is quantized into number of discrete slots and is selected by a. In cw modulation schemes some parameter of modulated wave varies continuously with message. Analog communications 26 other modulation methods amplitude modulation the amplitude of the carrier signal is controlled by the modulating signal pitfall of am.
Analog communication basics, reference books, pdf, viva. Pulse amplitude modulation has some applications, but it is not used by itself in data communication. Pulse digital modulation is also used in both analog and digital communications. Digital information can be generated from a computer but the information source can also be analog, as its the case of the voice. In this, the amplitude of carrier which is in the form of pulses is varied according to the amplitude of modulating the signal. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. In pulse width modulation, there are different types of modulation for analog and digital as shown below. Pulse amplitude modulation is the simplest form of modulation.
No information is lost, but the energy is redistributed in the frequency domain. Pdf analog,digital and pulse modulation techniques researchgate. Modulation techniques for mobile radio school of information science and engineering, sdu. In the pulse code modulation, analog signal is reconstructed to digital signal for ease of transmission by using the analog signal samples. The analog modulation techniques are mainly classified into pulse amplitude modulation, pulse duration modulationpulse width modulation, and pulse position. Analog modulation refers to the process of transferring digital low frequency baseband signal, like digital bitstream from computers over a higher frequency carrier signal such as a radio frequency band. The principle and design of a costeffective optical fiber communication system are proposed to support hybrid digital analog signal transmissions, by simultaneously using pulse width modulation. Digital pulse width modulation dpwm provides a digital to time domain conversion.
The main difference between analog and digital modulation is that an analog modulated signal can take up any value in a possible range whereas a digitally modulated signal can only take up one of a discrete set of values. Analog and digital pulse modulation techniques gate study. Analog communication pulse modulation tutorialspoint. In technical terms, pcm will transmit the analog in a digital from, whose signal is sampled at regular intervals of time and quantized at same quantum levels to digital code. Introducing pulse width modulation pwm what is pulse width modulation. If you continue browsing the site, you agree to the use of cookies on this website. The ltc6992 is a silicon oscillator with an easytouse analog voltagecontrolled pulse width modulation pwm capability. The original waveform amplitude is quantized with a resulting loss of information. These instances correspond to having analog channels that require the transmitted signal to be continuous in time, and to also be compatible with the bandwidth. Pulse coded modulation pcm is a form of modulation where there is no carrier, so. In cw modulation schemes some parameter of modulated wave varies. There are two types of modulation analog and digital. Introduction to communication system, need for modulation, frequency division multiplexing, amplitude modulation. Analog todigital converter analog signal mt analog samples pcm digital encoded signal.
We use modulation technique to alter signals in time and frequency to accomplish desired objectives. Analog and digital pulse modulation techniques need. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. Analog neuron circuits based on both frequency modulation and pulse modulation are investigated. Pulse code modulation is the heart of technology in communications in todays. Many signals in modern communication systems are digital also, analog signals are transmitted digitally. The signal is sampled at regular intervals such that each sample is proportional to the amplitude of the signal at that sampling instant.
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