In this chapter we will discuss ways of demodulating am, cw, fm, phase, and pulse. Overmodulation overmodulation is a condition that occurs when an excessive intelligence signal overdrives an am modulator making %m 100% because e i e c modulated carrier amplitude reach value greater than double of unmodulated value it produces a distortion known as sideband splatter, which results on transmission at frequencies outside. Chapter 4 automatic modulation recognition frequency and phase conventionally, modulation identification is performed by i decision theoretic dt approach ii statistical pattern sp approach iii spectral processing iv instantaneous amplitude, phase and frequency histogram techniques v hybrid scheme. Pdf an analytical phase noise model of charge pump mismatch in. Since the pfd and the charge pump generates the phase error. Pulse amplitude modulation pam, pulse width modulation pwm, pulse position modulation ppm digital modulation modulating signal is analog example. Chapter 4 frequency modulation linkedin slideshare. The amplitude, phase, or frequency of a carrier can be varied in accordance with the intelligence to be transmitted. Angle modulation includingfrequency modulation fm and phase modulation pm.
Pdf a low power phase locked loop pll based transmitter for wireless sensor application is presented in this paper. Amplitude modulation chapter 3 objectives at the conclusion of this chapter, the reader will be able to. The process of varying one of these characteristics is called modulation. Am wave in its most general formam wave, in its most general. The modulation depth am or frequency deviation fm is controlled by the signal level on the rearpanel modulation in connector. Introduction angle modulation modulation where the angle of a sinewave carrier is varied as a function of the intelligence amplitude. In addition to the basic building blocks that are the subject of this chapter, these circuit blocks often. Frequency modulation is widely used for radio transmission due to the fact that the signaltonoise ratio snr is large in this method of modulation and hence radio frequency interference is minimized. Frequency modulation, fm, variation of the frequency of a carrier wave in accordance with the characteristics of a signal. Am is defined as a process in which the amplitude of the carrier t i i d b t l li l ith b b dct a cc cos 2. Fm signals are used in technology such as radars, telemeters, eeg, radio broadcasting, satellite communication and magnetic tape recording systems. The big advantage of frequency modulation is its noise reduction ability, because most of noise is appeared as additional amplitude and in fm the amplitude of signal is hold fixed. Calculate modulation index, signal bandwidth, sideband frequencies and. Phase modulation pm is a modulation pattern for conditioning communication signals for transmission.
Although its old technology, it is still widely used in. The external modulation input has 3 db bandwidth of 100 khz. This chapter introduces a local oscillatorlo as a building block that finds place. Hapter modulation and demodulation mit opencourseware. The inherent problem of the fractionaln frequency synthesizer is that the. Explain the advantages and disadvantages of the different analog modulation techniques. 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. Modulation concep modulation is the process by which a message or informationbearing signal is transformed into another signal to facilitate transmission over a communication channel requires an auxiliary signal called carrier the modulation process. Analogue modulation the modulating signal and carrier both are analogue signals examples. The modulation scheme could be amplitude modulation am, frequency. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is sinusoidal. Frequency modulation while amplitude modulation synthesis changes the gain or volume of an audio signal, frequency modulation synthesis, or fm synthesis, is used to make periodic changes to the frequency of an oscillator. The three types of modulation, then are amplitude modulation, phase modulation, and frequency modulation.
Frequency modulation definition of frequency modulation. Frequency modulation is the process in which the frequency of the carrier signal is varied by the modulating signal while the amplitude remains constant. If you continue browsing the site, you agree to the use of cookies on this website. Pdf a calibrationless low error twopoint modulation transmitter. The pd drives a charge pump, which pumps constant current into the loop filter during the pulse opening windows. By successfully completing the occecc, you indicate that you have met the objectives and have learned. In chapter 5, system design considerations in frequency synthesis for high spectral. Modulation free download as powerpoint presentation.
Modulation has the effect of moving the baseband signal spectrum to be centered frequencies around the frequency of the carrier. Continuouswave cw modulation consists of onoff keying of a carrier wave. We discussed in chapter 10 why it is generally untenable to directly transmit baseband signals over communication links. Amplitude modulation am, frequency modulation fm, phase modulation pm 2. Therefore we only consider the case where the message signal mtis a sinusoidal signal. This chapter describes the essential principles behind. The transmitter adopts twopoint modulation architecture in highpass and. Identify the topology of in am the voltage of the carrier signal is varied to represent the information. Introduction 3 properties of an analog signal can be modulated by information signal.
Spectra have a typical trapezoidal shape in linear frequency and amplitude in decibels. We therefore assume mta mcos2 f mtfor pm and mta msim2 f mtfor fm. These two terms are introduced in the chapter of this volume entitled introduction to modelling with tims, in the section entitled multipliers and modulators. Amplitude modulation am and frequency modulation fm. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation the phase of a carrier signal is modulated to follow the changing signal level amplitude. Modulation in an am transmitter, intelligence superimposed on the carrier. Operation of fractionaln frequency synthesizers by. The comprehensive check questions are based on the objectives.
Transmission chapter 8 objectives at the conclusion of this chapter, the reader will be able to. Since frequency modulation is a nonlinear process, an exact description of the spectrum of an frequencymodulated signal for an arbitrary message signal is more complicated than linear process. 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. Frequency modulation frequency modulation is the process by which frequency of the carrier signal ct changes with respect to the modulating signal mt. Pulse amplitude modulation pam, pulse width modulation pwm, pulse position modulation ppm 3. Pulse modulation the modulating signal is an analogue signal but carrier is a train of pulses examples. Because many noise sources produce amplitude disturbances, am reception is very susceptible to them. Chapter 5 amplitude modulation so far we have developed basic signal and system representation techniques which we will now apply to the analysis of various analog communication systems. A typical f c for lowrate telephone line modems is 1800 hz approximate center of 300 3400 band, and for 1200 baud signaling 1200 pulses per. Phase modulation of the carrier with a message signal is equivalent to frequency modulation of the carrier with the derivative of the message signal. Chapter 4 modulation 1 what is modulation modulation is. Amplitude modulation introduction amplitude modulation is the simplest and earliest form of transmitters am applications include broadcasting in medium and highfrequency applications, cb radio, and aircraft communications basic amplitude modulation the information signal varies the instantaneous amplitude of the carrier am characteristics am is a nonlinear process sum and. Discuss the differences between am and angle modulation. 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.
Frequency modulation definition is modulation of the frequency of the carrier wave in accordance with speech or a signal. Fm modulated signal st is a nonlinear function of the modulating signal mt, thus it is known as nonlinear modulation process. In its simplest form, frequency modulation uses two oscillators. Of all the methods of impressing information onto a carrier signal, am is the oldest. We reiterate and elaborate on those reasons in section 14. It encodes a message signal as variations in the instantaneous phase of a carrier wave.
Frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The term and technology is used in both telecommunications and signal processing 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. All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. Frequency modulation objectives upon completion of this chapter, the student should be able to. Pulse code modulation pcm, delta modulation dm, adaptive delta modulation adm, differential pulse. The signal whose gain is being modulated is called the carrier, and the signal responsible for the modulation is called the modulator. Chapter 2 concerns all the general problems of frequency modulation, while chapter 3 deals with the propagation distortion, which is apparent in a variablevelocity guided transmission channel, and, which appears on an echoing path either in free space, or over a badly matched feeder.
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