Phase locked loop, pll fm demodulator or detector is a form of fm demodulator that has gained widespread acceptance in recent years. Fm modulation introduction in this lab, you will investigate frequency modulation fm and its properties. Fm demodulation is also called fm detection and sometimes the phrase fm discrimination is used, although this term tends to be used with older circuits and technology. Demodulation of wideband, lowpower fm signals darlington. However, these are representative of the types with which you will be working. A pll should have basic functional blocks like voltage controlled oscillator vco, phase comparator, low pass filter lpf and source follower. The proposed scheme is based on the basic principle of zero crossing zc for.
Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. The principles involved in their operation are similar to the other types. Pdf fm demodulation based on fm to pwm conversion with. If youve read the page on amplitude demodulation, the preceding paragraph may have caused you to realize that a quadrature demodulator is actually composed of two amplitude demodulators. Remember to set up the vco module in 100 khz vco mode. To see this, start with a sinusoidal modulating signal. In frequency modulation fm, the frequency of the carrier signal is varied as a function of the. Using matlab mfile and simulink to implement fm modulation and demodulation. But quadrature amplitude demodulation can capture the frequencyencoded informationthis is simply the rather interesting nature of iq signals. The design approach is to design the fm demodulator as if it were an analog phase lock loop. A technique for the robust demodulation of discrete fm signals in the presence of additive noise is presented. Division is normally achieved either by using the newtonraphson method or by. The frequency content and spectrum of this waveform is inherently bandlimited to a few kilohertz.
Implementation of fm demodulator algorithms on a high performance digital signal processor tms320c6711 dsp franz schnyder christoph haller. A noncoherent detector has only one input, namely, the modulated signal port. Mar 16, 2019 multiple choice questions and answers on modulation and demodulation. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. You will model the pll, and recover the message from the fm signal. Pdf amfm demodulation methods for reconstruction, analysis. The second section will be the design of the fm radio front end. To demodulate stereo audio using 38 khz, enable stereo demodulation. Fixedpoint dsp implementation of fm demodulationdecoding. Demodulation of fm slope and balanced slope detector.
With that all the components values has been designed and the complete circuit design for the fm demodulation is shown in the following. Note that although well concentrate on fm demodulation, similar methods are useful for general measurements of signal frequencies and for pm demodulation. Fm demodulation in v93000 will also be briefly introduced. Of course, you cannot apply ordinary amplitude demodulation to a frequency modulated signal. Frequency modulation offers improved performance over amplitude modulation, but it is somewhat more difficult to extract the original information from an fm waveform. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. It is a matlab demonstration of fm and am modulation and demodulation. January 22, 2019 january 25, 2019 by ian etheridge 2 comments. The telecommand system enables the control of launch vehicle during the flight. Quadrature detection, also known as fm discrimination and fm am conversion, is one of the most popular forms of fm demodulation due to its ease of implementation in an ic at low cost 2 25. Learn about two techniques for recovering the baseband signal from a frequency modulated carrier. Based upon least squares, the proposed technique is shown to improve the accuracy of instantaneous frequency estimation by 17 to 79% compared with the popular discrete energy separation desa, smooth desa and hilbert transformbased algorithms, e. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod. All digital fm demodulator kartik nair vtechworks virginia tech.
Fm demodulator circuits are found in any receiver that uses fm. Fm detector demodulators the fm detector demodulator treats the fsk signal as a simple fm signal with binary modulation. In an earlier semester project, four fm demodulation algorithms were developed and tested on their suitability. The fm demodulator is done with the help of a circuit called phase locked loop pll.
Here well examine how it is possible to demodulate these signals and recover the information. The modulated signal scope illustrates that the frequency of the modulator output, mod sig, varies with the amplitude of the input data. Frequency modulation frequency modulation is realized by varying signal frequency in accordance with the modulating signal or message, as in figure 1. Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier. The circuit in which restoration is achieved is called the detector or demodulator both of these terms are used in neets. Introduction frequency modulation is a form of modulation, which represents information as. The document is intended for users of the rf options on the system five. In this chapter we will discuss ways of demodulating am, cw, fm, phase, and pulse modulation. The demodulation module involves division and arctan for which there is no dedicated hardware on a fixedpoint dsp. Demodulation of fm is done by frequency discrimination method and phase discrimination method. Implementation of fm demodulator algorithms on a high.
Phase demodulation in phase modulation pm the intelligence is contained in the amount and rate of phase shift in a carrier wave. In this paper, different quadrature detection methods for fm demodulation like arc tan method, cordic vector rotation method etc. You should recall from your study of pm that there is an incidental shift in frequency as the phase of the carrier is shifted. There are far more efficient methods that can be used for fm detection demodulation.
The design approach is to design the fm demodulator as if it were an analog phase lock loop, only it will be implemented with digital components rather than their analog counter parts. This tutorial and accompanying applet allow you to experiment with fm parameters and see the results at different stages of demodulation. Quadrature detection, also known as fm discrimination and fmam conversion, is one of the most popular forms of fm demodulation due to its ease of implementation in an ic at low cost 2 25. In the laboratory, you will use function generator as vco.
The input data is a sine wave of frequency 4 hz and amplitude 1 v. In addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well. Digital modulation and demodulation fsk,psk,bpsk,qpsk techniques. Apr 16, 2017 demodulation of fm is done by frequency discrimination method and phase discrimination method.
The audio content from a received am radio wave can be recovered or demodulated by using a diode to rectify the signals and extract the audio content, or else via filtering to separate the highfrequency carrier signal from the audio content. Both modulation and demodulation involve a frequencyshifting. The essential parts of the fm demodulation system, which are demodulator unit, rf. Am and fm modulation and demodulation matlab ee501 youtube.
The continuous analog signal st is a baseband signal with the information content. I recently compiled and posted a project on describing how a theremin an electronic musical instrument can be built using the analog discovery 2, the digilent analog parts kit, and a. Figure 9 shows a functional block diagram for an fm detector type remove out of band interference and then limited to remove am inter ference. Once a signal has been modulated, information is retrieved through a demodulation process. Command system uses a fmfsk modulation on a uhfband link. 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. Experiment4 frequency demodulator preliminary work 1. Design and implementation of pll for frequency demodulation. In the part 12 we saw how it is possible to create signals which carry information by modulating the frequency or phase of a carrier wave. The quadrature fm detector or demodulator is used in many fm radios and receivers. Introduction to iq demodulation of rfdata september 15, 1999 page 3 of 1 introduction 1. Oct 15, 2017 i had already made a fm transmitter on 27mhz. Fm demodulation system, which are demodulator unit, rf unit and audio unit,were designed by hardware and the designed parts were examined.
Fm slope detection is a concept that can used be recover the modulation from an fm signal, but it is not widely used. Introduction frequency modulation fm has a long history of its application and is widely used in radio broadcast. Fm demodulation august 29, 20 by ashutosh bhatt frequency modulation fm is a technique in which the frequency of a transmitted waveform is varied according to the variations in the message wave. Command system uses a fm fsk modulation on a uhfband link. To demodulate rbds signals from the 57 khz band, enable rbds demodulation.
The fm broadcast demodulator baseband block demodulates a complex baseband fm signal by using the conjugate delay method, and filters the signal by using a deemphasis filter. In pulse position modulation the amplitude of the pulse is kept constant as in the case of the fm and pwm to avoid noise interference. The fmmodulated signal has its instantaneous frequency that varies linearly with the amplitude of the message signal. Of particular interest is the applet showing the output spectrum for an adjustable modulation index, based on the values of the bessel functions for the various sidebands. Abstract this paper addresses the fixedpoint dsp implementation of fm demodulation and decoding for the digital radio application. Balanced zerocrossing fm detector this is a hybrid circuit analog and digital combination if fi fc. Implementation of fm demodulator algorithms on a high performance digital signal processor tms320c6711 dsp franz schnyder christoph haller 11. The analytical signal for an analog frequency modulated fm signal is. 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.
To recover the message signal from the fm signal, frequency demodulation must be performed. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont. Understanding quadrature demodulation radio frequency. There are many types of modulation so there are many types of demodulators. In the demodulator circuit the vco generates a frequency which matches the original carrier frequency and compares the phase of that with received fm wave using the. 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. Get pdf 16357k get pdf 16357k some theoretical aspects of the demodulation of wideband, lowpower fm signals are discussed. Multiple choice questions and answers on modulation and. Multiple choice questions and answers by sasmita march 16, 2019 multiple choice questions and answers on modulation and demodulation in addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well. An important concept in the understanding of fm is frequency deviation. To transmit stereo music, fm is enhanced by stereo multiplexing which carries both l. This paper attempts to present the fm demodulation based on fm to pwm conversion with voltage gain control vgc. In an earlier semester project, four fm demodulation algo.
Once the signal has been received, filtered and amplified, it is necessary to recover the. Fm radio receiver with digital demodulation a senior project presented to the faculty of the electrical engineering department california polytechnic state university, san luis obispo. What is fm demodulator an electronic circuit in which frequency variations of modulated signals are converted to amplitude variations first, with the help of tuned circuit and then original information is extracted with the am demodulation techniques say diode detector. During this lab you will create an fm signal by modulating an audio waveform onto a carrier, examine the spectrum of the modulated carrier, evaluate the modulated carrier when the modulation index is varied and. The output signal via demodulator may describe the sound, images or binary data. You are free to choose the frequency and magnitude of the carrier and message signals. An am radio signal can be demodulated by rectifying it to remove one side of the carrier, and. There are different types of modulation and so are demodulators. Frequency modulation is a form of analog angle modulation in which the baseband information. The technique used to demodulate the fm signal is the popular phase lock loop demodulator.
But the only things i dont understand is the following. The pll was operated as a complete if strip, limiter, and detector employed in fm receivers. It is assumed that a bandlimited, continuous, analog signal is supplied to the modulator and is recovered to a fidelity suitable for television, telephone, or carrier telephone. The signal output from a demodulator may represent sound an. There are more than the three types of fm demodulators presented in this chapter. Implementation of fm demodulator algorithms on a high performance digital signal processor. Pdf bluetooth demodulation algorithms and their performance.
Fm demodulation is a key process in the reception of a frequency modulated signal. Slope detector can be constructed with the help of a tuned amplifier and an envelope detector. Because fm is a nonlinear modulation it is highly sensitive to the frequency content of modulating signal. Quadrature detection methods for fm demodulation ieee. Demodulation of fm signal there are two predominant methods for demodulating an fm signal. As a result the output waveform for every part was measured in order to ensure that the design is compatible with the required conditions. Demodulation is extracting the original informationbearing signal from a carrier wave. Fixedpoint dsp implementation of fm demodulationdecoding h. Fm transmission to amplify the highfrequency content of the message signal. Amfm demodulation methods for reconstruction, analysis and motion. In any radio that is designed to receive frequency modulated signals there is some form of fm demodulator or detector. You will now briefly study phase demodulation which uses the same basic circuitry as fm demodulators.
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