Therefore we only consider the case where the message signal mtis a sinusoidal signal. Phase and frequency modulation consider a signal of the form x cta c cos2. The spectrum consists of sidebands, spaced by u m, with phase dependent on sideband, and amplitude given by the bessel functions. Fm modulation and demodulation will be presented and you will implement two types of demodulators, the frequency discriminator and the phase locked loop. A linear timeinvariant system having a transfer function. Phase and frequency modulations are techniques that modify the instantaneous phase and frequency, respectively, of a sinusoid in a way dictated by an information signal f. In the frame of the rotating carrier vector, the sidebands modulate the phase. Phase modulation pm is a modulation pattern for conditioning communication signals for transmission. Even for the pure tone modulation, the fm spectrum consists of an in nite number of sidebands whose signs change from one sideband to the next one and whose amplitudes are given by the horrible bessel functions. The amount of phase shift is proportional to the message signal amplitude. We will assume that the baseband message signal mt is band limited with a cuto. Modulation is the act of changing a signal to transmit useful data. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Frequency modulation the frequency of the carrier signal is proportional to the modulating signal phase modulation the phase of the carrier signal is proportional to the modulating signal 2 cos 0.
Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. The spectrum of an fm signal is quite complicated and is dependent on mf. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. When the carriers phase changes, frequency deviations also occur. There are many ways to embed a message in a carrier. Difference between frequency modulation and phase modulation. There are three aspects of a signal that can be modulated. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. Relationship between phase modulation pm and frequency modulation fm. Frequency modulation definition, applications, advantages. Phase modulation and frequency modulation derivation, wave forms, relation between fm and pm. The envelope is a constant so the message cannot be in the envelope.
The bessel function computes amplitude spectrum only. Thus, ssb modulation requires half the bandwidth of am or dsbscam modulation. The message signal can be scaled by a constant factor as well. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. The fact is that theres only so much modulation that can be reasonably covered in the last several chapters of this course, and am is the easiest to visualize and demonstrate. In phase modulation it is to be noted that there is a resultant frequency deviation which varies directly with the modulating frequency. Phase and frequency modulation for angle modulation, the modulated carrier is represented by. Frequency shift keying fsk phase shift keying psk all of these techniques vary a parameter of a sinusoid to represent the information which we wish to send. Jun 02, 2020 difference between frequency modulation and phase modulation in this article we are going to understand the difference between fm and pm.
Phase modulation the instantaneous carrier phase changes with the modulating waveform. Amplitude modulation am frequency modulation fm phase modulation pm click on the links given above to know more. We shall focus more on frequency modulation in this course and less on phase modulation. Frequency versus amplitude modulation l frequency modulation fm l most popular analog modulation technique l amplitude of the carrier signal is kept constant constant envelope signal, the frequency of carrier is changed according to the amplitude of the modulating message signal. In either case, the frequency of the modulated signal changes as a function of mt. A sinusoid has three different parameters than can be varied. Comparing and contrasting amplitude, frequency, and phase. It must instead lie in the variation of the cosine argument with time. Here we will be modulating the frequency of the carrier wave with a. Chapter 6modulation techniques shandong university. Both fm and pm waveforms are identical except for a phase shift. It encodes a message signal as variations in the instantaneous phase of a carrier wave. Lecture 2829 fm frequency modulation pm phase modulation. An fm signal with a modulation index 9 is applied to a frequency tripler.
In ask, the amplitude of the signal is changed in response to information and all. Phase modulation pm is used primarily in digital communication. The modulator circuits can be used for demodulation, but replacing the bpf by a lpf of bandwidth b hz. Voltage controlled oscillator, entrainment, phase modulation, rf mems introduction frequency sources that are tunable in frequency and phase are essential parts in modern communication and radar applications. Phase resolved, phasemodulation, or phase sensitive lifetime measurements are based on the use of a continuous, sinusoidally modulated excitation source and phase sensitive detection figure 7. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Modulation modulation is the process whereby some characteristic of one wave is v aried in accordance with some characteristic of another wave. Also consider modulating the phase replace phase with a message signal x m t. In pm, carrier signal modulation occurs when the carrier signal changes its phase and frequency with the changes in the message signal amplitude and frequency. Amplitude, phase, and frequency modulation ieee xplore. Hence info is carried in the phase or frequency of the carrier. Optical phase modulation pm and frequency modulation fm are promising techniques that can improve system performance.
Look at the signal generator manual to see how to get an fm signal. Phase modulation pm is that form of angle modulation in which the angle. In this experiment, we will use a famous chip, the lm 566c to generate the fm signal. The experimentally measured parameters are the modulation m and the frequency dependent phase shift. Modulationtypesamplitude,frequency,phase modulation. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. By frequency modulation, fm, the variation in instantaneous frequency from the carrier frequency is directly controlled by the baseband signal as shown by eqs. A radio frequency signal consists of an oscillating carrier in the form of a sine wave is the basis of the signal. The simplest form of fsk is binary fsk bfsk, in which a carriers frequency is. Linear, low noise microwave photonic systems using phase.
As we already know, phase modulation produces frequency modulation. The basic types of modulation are angular mo dulation including the special cases of phase and frequency modulation and amplitude modulation. Fm frequency modulation pm phase modulation continued ee44510 22 narrowband fm only the j o and j 1 terms are significant same bandwidth as am using eulers identity, and. But, a very important point may be noted here that the frequency modulation fm is produced by pm if and only if the phase shift is being varied.
Pdf phase shifts and intensity dependence in frequency. Amplitude and frequencyphase modulation i always had di culties in understanding frequency modulation fm and its frequency spectrum. In this dissertation, i discuss an optical ltering approach to demodulation of pm and fm signals, which does not rely on high frequency electronics, and which scales in linearity with increasing photonic integration. Linear, low noise microwave photonic systems using phase and. Bandwidth and spectra of phaseandfrequencymodulated waves.
The modulation index in the output signal will be a 0 b 3 c 9 d 27 gate 1996. For digital phase modulation, we only modulate the phase of the carrier. The receiver must generate a carrier frequency in phase and frequency synchronization with the incoming carrier. Frequency modulation is the process of varying the frequency of the carrier signal linearly with the message signal. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc. Modulation allows for the designated frequency bands with the carrier frequency at the center of the band to be utilized for communication and allows for signal multiplexing. We therefore assume mta mcos2 f mtfor pm and mta msim2 f mtfor fm.
We will use a trig identity to expand this expression. The amplitude is the power or intensity of the signal, the frequency is how often the signal repeated itself, and the phase describes where in the cycle the waveform is with respect to time. Graphical representation of a frequency modulated signal the envelope is constant, and the frequency varies with the modulation. Angle modulation frequency modulation university of. Amplitude modulation am is an analog and linear modulation process as opposed to frequency modulation fm and phase modulation pm. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation. With the aid of electronic andor opticaldelay lines. To determine the sudden phase shift or lack thereof see kpmt for pm. When we have a voltage wave form with a variable frequency, this has the form.
Since the three variables are the amplitude, frequency, and phase angle, the modulation can be done by varying any one of them. Example commercial fm signals use a peak frequency deviation of. This type of demodulation is therefore called coherent demodulation or detection. The modulator shown on slide 76 is also a block diagram for a demodulator that implements the formula at the bottom of the previous slide if the input mt is replaced by the received signal. This is further divided into frequency and phase modulation. Phase modulation frequency is not the only choice in the argument of the sinusoid for modulation. This video shows the concept about amplitude modulation, frequency modulation and phase modulation with examples. Like am synthesis, frequency modulation requires a carrier wave and a modulator wave. V t v0 cos c t v0 cos c t mcos m t m is the modulation index and u m is the modulating frequency. Then the required channel bandwidth for an ssb signal is w. Frequency modulation is equivalent to a phase modulation in which the phase shift is inversely proportional to. For fm, the maximum frequency deviation occurs when modulating signal is at its peak values. In frequency modulation fm, the instantaneous frequency deviation of the carrier is proportional to the mess age signal.
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