There are different types of modulation and so are demodulators. This demodulator is more complex than most asynchronous demodulators. Angle modulation ch16 angle modulation host modulation therapy digital modulation schemes ch16 angle modulation detection estimation and modulation theory part i pdf sinusoidal pulse width modulation inverter arduino. No information is lost, but the energy is redistributed in the frequency domain. Analog communication lab manual, prepared by nakka. 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. 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. This chapter describes the essential principles behind modulation and demodulation, which we introduced briefly in chapter. The theory behind multichannel am radio for k 1k, let x kt be a continuoustime signal with fourier transform x kj. Amplitude modulation a1 49 you will see in this experiment, and in others to follow, that there is no problem in generating an am signal with a depth of modulation exceeding 100%, and without any rf distortion whatsoever. Pdf simple, ultralow distortion digital pulse width modulator. Double sideband suppressed carrier dsb sc modulation. This chapter describes the essential principles behind. Pulse center two edge modulation phase correct pwm.
Modulation and demodulation medium, it would be dif. Then inner products dot products are 1 1 0 can interpret inner product as projection of vector 1 v1 onto vector 2 v2in other words, inner product of v1 and v2 tells us how much of vector 1 is there in the direction of vector 2. The term detection is the older term dating back to the early days of radio. Both amplitude and phase of ft carry information of ft. To study and perform pulse width modulation and demodulation. This conforms to the expectation as the maximum and minimum peak of the modulated signal waveform varies proportional to the amplitude of the modulating signal. Review pulse train bandwidth s ingle pulse of duration. In general, the larger the command signal, the wider the pulse. Fsk frequency shift keying d1 63 fsk in f 1 f 2 decision out figure 4. In a pcm stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. Typical modulation system the reverse process is called demodulation.
To recover the original audio signal from a pwm signal, a decoder or demodulator is need in the receiver circuit. The square generator and the monostable multivibrator circuits were used to generate the pwm signal. As described in previous pages, single sideband is a form of amplitude modulation where the carrier and one sideband have been suppressed or reduced in level. User manual for pulse width modulation and demodulation. There will be a minimum frequency separation required of the two tones. 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. At the broadcasting station, modulation is done to transmit the audio signal over larger distances to a receiver. Pwm converts an audio signal into a sequence of pulses having constant amplitude, but the width is proportional to amplitude of. To understand the operation theory of pcm demodulator. Pwm converts an audio signal into a sequence of pulses having constant amplitude, but the width is proportional to amplitude of an audio signal. In this method, the pulse center is fixed and both edges of the pulse is modulated. Pulsecode modulation pcm is a method used to digitally represent sampled analog signals.
This lab introduces students to communications theory with amplitude modulation and demodulation. Pulse width modulating signal can be generated using a comparator as shown in the figure 4 a. Then as the audio signal amplitude is changed to 150 mvpp, the percentage modulation dropped to around 30%. Terms like diode detector, synchronous detector and product detector are widely used. Hapter modulation and demodulation mit opencourseware. Introduction frequency modulation is a form of modulation, which represents information as. Print means choose the print command in the file menu. The original waveform amplitude is quantized with a resulting loss of information. The meaning of source coding is the conversion from analog signal to digital signal. Modulation and demodulation pdf on the various aspects of modulation and demodulation. It is primarily useful for optical communications systems, which tend to have little or no multipath interference. Analysis of random pulsewidth modulation techniques for power. To study and perform pulse position 6 to study and perform pulse code modulation and demodulation. Pulseposition modulation ppm is a form of signal modulation in which m message bits are encoded by transmitting a single pulse in one of possible required time shifts.
After converted to digital signal, it is easy for us to process the signal such as. We can also get back our analog signal by demodulation. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. The longer the switch is on compared to the off periods. Topics pulse, modulation, theory, pwm, power ratio. 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. The pulse may take any real voltage value that is proportional to the value of the original waveform.
Vectors and modulation cse 466 interfacing 3 spose m and n are orthogonal unit vectors. If modulation index is greater than 1, or the modulation percentage is more than 100%, it is called over modulation. The demodulation of shaped noise introduced by the. Frequency division multiplexing, fdma amplitude modulation and demodulation. Pulse modulation timedivision multiplex tdm continued receivers for timemultiplexed pam signals requirement 2 when a large number of pam signals are timemultiplexed together, the width of the sampling pulses must be made very narrow. Sampling theorem determines the necessary conditions which allow us to change an analog signal to a discrete one. Capacityapproaching codes demodulation line coding modem anm pom pam pcm pdm. Modulation can be defined as the process of impressing information from a modulating signal onto another signal called the carrier. If the received carrier phase is assumed to be constant, each of the seven reference values will have to be shifted only once at the beginning of the simulation.
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 operation theory of pcm modulation pcm modulation is a kind of source coding. That is, there are only two possible states, represented by logic 1 high and logic 0 low. Pulsewidth modulation pwm, or pulseduration modulation pdm, is a method of reducing. Infrared remote control modulation and encoding theory. Modulation allows us to transmit multiple signals in the same medium i. Analog communicationpulse width modulation and demodulation is proposed to user friendly to process the experiments and the trainer had all internal features like message signal, carrier signal, power supply etc.
Theory shows that in order to transmit a wave effectively, the length of the. A pulsemodulated signal in radar may be detected by a simple circuit that detects the presence of rf energy. The resulting signal is called the modulated signal in general, it is a bandpass signal. The simulation for the same was carried out using ngspice. Pwm have not yet been properly analyzed from a theoretical point of view. Tcom 370 notes 995 modulation and demodulation modems for data transmission over analog links 1. The baseband signal is not preserved in the envelope of the am signal and therefore, the recovered signal is distorted at the output of the receiver. Pulsewidth modulation the output of a pwm amplifier is either zero or tied to the supply voltage, holding losses to a minimum. 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. The bandwidth of each is dependent on the message bit rate. Pcm is in binary form, so there will be only two possible states high and low0 and 1.
Then, students will use labview to program an am demodulator and use it to explore and visualize the. The transmission bandwidth required by dsb sc is b t2b. Pulse width modulation pwm generation, applications. Pulse width modulation pwm is a modulation technique, which converts an analog signal into a digital signal for transmission. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. This is true no matter how complex the analog waveform happens to be. The larger fraction of the pulse energy is near 0 frequency. In order to demodulate single sideband, ssb, it is necessary to reintroduce the carrier. This is repeated every t seconds, such that the transmitted bit rate is bits per second.
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. Students will explore the mathematical theory behind amplitude modulation and use the analog discovery 2 to visualize the effects of amplitude modulation in the time and frequency domains. Using matlab mfile and simulink to implement fm modulation and demodulation. The results obtained have been presented at the end of this document. Circuits that are capable of this were covered in this chapter in the cw detection discussion. Process by which a property or a parameter of a signal is varied in proportion to a second signal. Abstract this document gives an overview of how pulse width modulation and demodulation can be performed using bipolar junction transistors and operational amplifiers. The amplitude of the carrier remains constant phase modulation pm another form of analog modulation technique which we will not discuss. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave.
The process of recovering the original signal from the modulated wave is known as demodulation or detection. Pulse width demodulation objective to study the and implementing a pulse width demodulator. 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. But the term demodulation tends to be used more widely when referring to the process of extracting the modulation from the signal. Sampling theorem and pulse amplitude modulation pam. Pdf on may 1, 2006, bruno putzeys and others published simple, ultralow distortion digital. But we are getting ahead of ourselves, as we have not yet even defined what am is. Depending on the requirement the width of the pulse is modulated adjusted.
Pdf this article tell detail about pwm demodulation its circuit diagram, block diagram and. Modulation and demodulation pdf modulation and demodulation ch16 modulator demodulation 16. In the doublesideband suppressedcarrier transmission dsb sc modulation, unlike am, the wave carrier is not transmitted. One approach to reduce this interference, known as frequencydivision multiplexing, allocates different carrier frequencies to different users or for dif. To study pulse amplitude modulation and demodulation. Pulse code modulation pulse code modulation pcm is a digital scheme for transmitting analog data.
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