Amplitude modulation am, demodulation and their circuit. The demodulated signal might require amplification and further filtering to achieve good quality message signal. Its still used in radio systems to transmit audio signals although it has lesser in popularity compared to fm due to its lower signal to noise ratio. Pulseposition modulation ppm is a signal modulation used for both analog and digital signal transmissions. 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 goal of this experiment is to become familiar with fm modulation and demodulation. In the double polarity pulse amplitude modulation, the output of modulating signal will have both positive and negative ends. You need to somehow convert this in to a wave that travels over the wire. Amplitude modulation am, demodulation and their circuit implementations. Pulse width 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. The most simple demodulation principle of pwm signals are describes in this article.
Pulse width modulation pwm generation, applications. As the duty cycle changes to deliver more or less power, efficiency remains essentially constant. This process of imposing an input signal on a carrier wave is known as 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 positive. The basic idea is to vary the input signal which is supplied to. After converted to digital signal, it is easy for us to. Abstract this document gives an overview of how pulse width modulation and demodulation can be performed using bipolar junction transistors and operational amplifiers.
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. Am modulation and demodulation with circuit and output. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. This is divided into analog pulse modulation and digital pulse modulation. To understand the operation theory of pcm demodulator. In general, the larger the command signal, the wider the pulse. This video is about the demodulation detection of pulse width modulation pwm and pulse position modulation ppm. Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. Recognize pulse amplitude and pulse width modulated signals, and do simple experiments.
Capacityapproaching codes demodulation line coding modem anm pom pam pcm. We can also get back our analog signal by demodulation. Synchronous modulation and demodulation low dc current may be transformed into a high voltage dc by simple chopper action. One method is that the pwm signal must first be converted to a pulseamplitude modulation. Frequency modulation is an analog modulation technique in which the frequency of carrier wave is varied in accordance with the instantaneous value amplitude of. Demodulation of pwm and ppm block diagram and waveform. 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. In this video you will learn the block diagram of pwm and ppm.
The longer the switch is on compared to the off periods. Pwm coding can be done using 741 op amp that we discussed before. Demodulation demodulation is the act of extracting the original information bearing signal from a modulated carrier wave. The demodulator is composed of a lowpass filter, whose. The term detection is the older term dating back to the early days of radio. The simulation for the same was carried out using ngspice. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. This lecture introduces phase characteristic in the frequency response, and the derivation of dtft for a rectangular pulse. Pulse width modulation and in position ppm, pulse position. Generating pwm pulse width modulated wave using 555 timer ic. 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. Terms like diode detector, synchronous detector and product detector are widely used.
Pwm is the first type of ptm and is discussed in the previous content. The key difference between modulation and demodulation is that modulation is done at the transmitter side while demodulation is done at the receiver side of a communication system. Pulse width demodulation theory with block diagram and wave form. There are two common techniques used for pulsewidth 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.
General information on pulse width modulation demodulation. In this method the average voltage delivered to the load is controlled by varying the duty cycle of the rectangular wave. Explain generation and demodulation of pam, ppm and pwm with. Demodulation is extracting the original informationbearing signal from a carrier wave. Analog communicationpulse width modulation and demodulation is proposed to user friendly to process the experiments and the trainer had all internal. To design and setup an frequency modulator circuit using 555 ic and measure its modulation index. General information on pulse width modulationdemodulation. Pulse width modulation pwm is a modulation technique, which converts an analog signal into a digital signal for transmission. Defining the term, we can say that pwm is the way we control a digital signal simulating an analog one, by. To involve data information or speech information, another wave has to be imposed known as input signal above the carrier wave. There are many types of modulation so there are many. When input noise power is quite large we would be inclined to use fm and allows a sacrifice of bandwidth for the sake of improved. This problem can be avoided by using pulse width modulation. 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.
The pwm generation is explained with the help of the fig5 given below. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. Frequency modulation fm frequency modulation is the process of varying the frequency of a carrier wave in proportion to the amplitude of a baseband signal. Pulse width modulation pwm, or pulseduration modulation pdm, is a method of reducing. Fm demodulation using pll in fm modulation when the bandwidth becomes so large that the input noise power is relatively large, the performance of the fm system degrades rapidly and the system exhibits a threshold. Frequency shift keying fsk modulation and demodulation techniques duration. 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.
Principles of communication modulation a signal can be anything like a sound wave which comes out when you shout. Here im going to discuss one of the simple technique to generate pwm using the 555 timer ic. Synchronous modulation and demodulation photo optical. The results obtained have been presented at the end of this document. The operation theory of pcm modulation pcm modulation is a kind of source coding. This method is widely used for optical communication systems such as optic fiber and ir remote controls, where efficiency is required and little or no external interference occurs.
Pulse width modulating signal can be generated using a comparator as shown in the figure 4 a. Pwmf modulated signal, middle pwm signal demodulation. Here the modulated pwm wave is applied to the decoder system for getting the message signal. User manual for pulse width modulation and demodulation trainer. In telecommunications and signal processing, frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave in analog frequency modulation, such as fm radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the.
Modulating signal forms one of the input to the comparator and the other input is fed with a nonsinusoidal wave or sawtooth wave. Principles of communication modulation tutorialspoint. Content introduction what is modulation types of modulation amplitude modulation modulation index amplitude demodulation circuit diagram about project conclusion 3. Pulsewidth modulation the output of a pwm amplifier is either zero or tied to the supply voltage, holding losses to a minimum. Key differences between modulation and demodulation 1.
Each channel sharing scheme a set of basis vectors. Pulse amplitude modulation pam pulse width modulation pwm pulse position modulation ppm. The basic theory behind pulse width demodulation is that converting the pwm signal to pam pulse amplitude modulation signal. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. This shout can be heard only up to a certain distance. An example of how to send a pulse over a lowpass and a bandpass channel opens discussion about modulation and demodulation.
Pcm is in binary form,so there will be only two possible states high and low0 and 1. Pwm signal can be generated by using a comparator, where modulating signal and sawtooth signal form the input of the comparator. Am modulation and demodulation with circuit and output 1. 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. The message signal is, for example, a function of the sound to be. Although pwm is also used in communications, its main purpose is actually to. The concepts of amplitude modulation, modulation and demodulation, along with their differences is explained below. The pulse width demodulation circuit with the first order low pass filter used for the demodulation is given in the following figure. The meaning of source coding is the conversion from analog signal to digital signal. Pulse amplitude modulation is the basic form of pulse modulation in which the signal is sampled at regular and each sample is made. The amplitude of the carrier remains constant phase modulation pm another form. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Pulse width modulation pwm is a technique to generate low frequency output signals from high.
To understand the generation of the ppm signal, it is necessary to understand pulse width modulation pwm or pdm. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Pwm, or pulse width modulation is a powerful way of controlling analog circuits and systems, using the digital outputs of microprocessors. Pulse width demodulation theory with block diagram and. Pulse width modulation pwm or pulse duration modulation pdm or pulse time modulation ptm is an analog modulating scheme in which the duration or width or time of the pulse carrier varies proportional to the instantaneous amplitude of. But the term demodulation tends to be used more widely when referring to the process of extracting the modulation from the signal. Pulse modulation is a technique in which the signal is transmitted with the information by pulses. Circuit diagram of pulse width demodulation circuit with low pass filter. Pulsewidth modulation pwm is a modulation process or technique used in most communication systems for encoding the amplitude of a signal right into a pulse width or duration of another signal, usually a carrier signal, for transmission. Pulse width modulation with frequency changing emo.
1201 983 198 427 1553 1002 934 1536 1380 505 283 628 681 1296 1140 794 675 762 497 1039 208 463 781 1249 264 1568 1205 85 992 1562 1387 1093 78 1157 1547 21 1357 522 319 1222 684 1201 1241 1362 1472