Fm modulation demodulation with pll general description package outline njw2307 is a fm modulation demodulation ic for audio signal in full duplex communication that operates from 3. So, the message signal of the above derivative is contained in the frequency of the sinusoid and also in its magnitude. Demodulation of fm slope and balanced slope detector. A pll can lock onto the frequency of an incoming waveform. Fm is considered an analog form of modulation because the baseband signal is typically an analog waveform without discrete, digital values.
In this experiment, we will use a famous chip, the lm 566c to generate the fm signal. Fm is less vulnerable to signal interference from adjacent channels. There are different types of modulation and so are demodulators. In the simulation experiment section2, we used the vco to demodulate the information signal to make life easier. Lets assume that by looking at the transfer curve obtained, you have decided that the fm carrier should fall at 452 khz. The demodulator extracts the original baseband signal from the received modulated signal to summarize. 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. Menu capture and decode fm radio fraida fund 10 february 2016 on education, software defined radio, wireless. To understand the theoretical foundations for angle modulation as well as frequency modulation fm and demodulation. Fm demodulation is a key process in the reception of a frequency modulated signal. Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier. A complex baseband fm signal is generated from the conventional fm signal 1 as shown in figure 1. Upon completion of the experiment, the student will. Fm detectortype demodulators are somewhat complex for fdm work and cannot generally be used with interleaved fdm signals.
The most basic frequency demodulator consists of a frequency discriminator, which is a differentiator followed by an envelope detector, as shown in figure 3. Frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The way in which a phase locked loop, pll fm demodulator works is relatively straightforward. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. Jun 05, 2015 guide students to gain a working understanding of theories such as demodulation, bandwidth, and carsons rule.
Understanding quadrature demodulation radio frequency. It should take about 60120 minutes to run depending on your familiarity with the reference material, but you will need to have reserved that time in advance. Is a nonlinear function of the modulating signal mt, which makes frequency modulation a nonlinear modulation process. You will model the pll, and recover the message from the fm signal. Frequency modulation fm is a form of modulation in which changes in the carrier wave frequency correspond directly to changes in the baseband signal. This information recovery process is known as demodulation or detection. Using matlab mfile and simulink to implement fm modulation and demodulation. 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. The main reason behind using the fm modulations by the radio stations is the quality of the signal that can be recreated in the fm receiver. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators. 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. The second section will be the design of the fm radio front end. The pll demodulates the fm signal using feedback force a voltagecontrolledoscillator vco to remain in phase with the carrier of the incoming signal. It requires no changes to the basic phase locked loop, itself, utilising the basic operation of the loop to provide the required output.
However the fm modulator and demodulator circuits are complex compared to other modulation and demodulation techniques. Apr 16, 2017 demodulation of fm is done by frequency discrimination method and phase discrimination method. I and q components in communications signals and single. The block diagram of square law demodulator is shown in fig 2. The continuous analog signal st is a baseband signal with the information content voice or music to be transmitted. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave. The total mixing operation produces a real inphase and an imaginary quadraturephase baseband component. A pilot signal is transmitted outside the passband of modulated signal.
If you want a starting point, the equivalent function in matlab is fmdemod if you have the communications toolbox. Learn about two techniques for recovering the baseband signal from a frequencymodulated carrier. Because the dfsk signal transmits only one frequency at a time, transmitter power efficiency can be much higher than an fdm transmitter, which has a linearity requirement to prevent intermodulation of tones. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. An important concept in the understanding of fm is frequency deviation. The am demodulator can be implemented by utilizing a balanced modulator.
Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Implementation of fm demodulator algorithms on a high. Slope detector can be constructed with the help of a tuned amplifier and an envelope detector. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. To keep the compatibility the new device should be able to perform the analog modulation. Some phase modulation and quadrature amplitude modulation formats have a higher spectral efficiency for data transmission than frequency shift keying, a form of frequency modulation. In addition to audio signal, it can also be used in data pulse. Fixedpoint dsp implementation of fm demodulationdecoding. Consequently, unlike amplitude modulation, the spectrum of an fm signal is. In this experiment you will demodulate the fm signal using either slope detector or phase locked loop pll.
This circuit takes in frequency modulated rf signals and takes the modulation from the signal to output only the modulation that had been applied at the transmitter. Once the signal has been received, filtered and amplified, it is necessary to recover the. 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. The goal of this experiment is to become familiar with fm modulation and demodulation. Because both algorithms demand the same pre and after signal preparation, the demodulation. Then retune the transformer so that the fm carrier frequency falls at 455 khz.
The signal to noise ratio is comparatively very high at the output of fm demodulator circuits. The design approach is to design the fm demodulator as if it were an analog phase lock loop. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. Once a signal has been modulated, information is retrieved through a demodulation process. To recover the message signal from the fm signal, frequency demodulation must be performed. The process of recovering the message signal from the received modulated signal is known as demodulation. We call this type of modulator as synchronous detector or product detector. Demodulation is extracting the original informationbearing signal from a carrier wave. Introduction frequency modulation is a form of modulation, which represents information as. Modulation and demodulation technology innovation and.
The analytical signal for double sideband, large carrier amplitude modulation dsblc am is. This senior project paper reports on the design and implementation of an fm receiver front end and of a digital phase lock loop design to demodulate fm broadcast signals. This process of detection is exactly opposite to that of modulation. There are two types of am detectors or demodulators such as. But quadrature amplitude demodulation can capture the frequencyencoded informationthis is simply the rather interesting nature of iq signals. Teach the basics of frequency modulation and demodulation. Discuss the requirements for recovery of intelligence from an am signal and describe the theory of operation of the following am demodulators. The fm is a very popular technique since they are widely used by the fm radio stations. Disadvantage of fft filters all the data manipulation is processor intensive and delays are an issue.
In coherent detection or synchronous demodulation both the phase and frequency of carrier must be known at the detector. Demodulation for communications simulation matlab demod. However the fm modulator and demodulator circuits are complex compared to other modulation and demodulation. Fm, on the other hand, encodes all of the information in the temporal characteristics of the transmitted signal. This chapter describes the demodulation methods of am signal and fm signal. Remember to set up the vco module in 100 khz vco mode.
Finds the pulse widths of a pulsewidth modulated signal y. However, for a small class of signals specifically designed for pll demodulation, pll demodulators may perform better than fm detector demodulators. Phase locked loop fm demodulators are used in many radio receivers both domestic and professional for the demodulation of fm signals. The analytical signal for an analog frequency modulated fm signal is. A noncoherent detector has only one input, namely, the modulated signal port. Fm demodulation in v93000 will also be briefly introduced. The message is recovered as the control input of the vco 4.
It converts the instantaneous frequency deviation in an fm signal to. This experiment is meant to teach the basics of fm signal processing. Each channel sharing scheme a set of basis vectors. January 22, 2019 january 25, 2019 by ian etheridge 2 comments. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. In the modulating process the carrier wave is generated by the lo circuit, and then combined with the baseband signal inside the mixer. To implement the simulink models for fm including a basic sinusoid and a multimedia file music to analyze each signal in time and frequency domains using time scope and spectrum analyzer. Frequency modulation the fm signal st defined by equation 2.
Jan 18, 2012 when a modulated signal arrives at the receiving antenna, the embedded information must somehow be extracted by the receiver and separated from the hf carrier signal. Phasemodulation and demodulation techniques are more complex than modulation and demodulation based on amplitude and frequency. The left column is the shaped baseband signal spectrum, and the middle column is the spectrum of the modu lated signal that is transmitted and received. The angle of the fm signal, assuming the value is 0 at t 0, is. This complex representation of fm signal has a major advantage in the design of fm demodulator, which involves division and arctan. 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. 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.
Modulation is the process of impressing a lowfrequency information signal baseband signal onto a higher frequency carrier signal modulation is done to bring information signals up to the radio frequency or higher signal. Of course, you cannot apply ordinary amplitude demodulation to a frequency modulated signal. Its amplitude a, which leads us to the class of systems designated as amplitude. You cant easily cook up firiir filters, for instance. If you do not specify the opt parameter, modulate uses a default of opt pimaxmaxx so the maximum phase excursion is. Chapter 5 radio frequency demodulation pdf version. Dutton ee3 winter 2004 3 3 fm demodulation using the pll now that youve seen how the pll tracks a signal, we will explore one of its applications, fm demodulation. Fsk demodulation the demodulation methods for fsk can be makes all positive voltages into binary 1s and all negative voltages into binary 0s. Fm can be created by applying message signals directly to a voltagecontrolled oscillator vco, so that the vcos output will be a function of the input signal. Signal manipulation based on frequency removing bin 210 212 performing an ifft inverse fast fourier transform and sending the data stream to a dac will recreate the analog signal without the carrier. Introduction to iq demodulation of rfdata september 15, 1999 page 6 of 3. In this case, using the 1,0,1 coefficient differentiators, the fm demodulator is simplified to that shown in figure 61b where the scaling operation is multiplication by. Abstract analog modulations are more and more replaced by digital ones.
Frequency modulation 1 objective to understand the principles of frequency modulation and demodulation. This means that, in order to move the fm carrier up to 455 khz, the whole response curve. Passing the derivative of the fm signal through an envelope detector will give the desired message signal at the output. Therefore, the following block diagram is an fm demodulator. By the time youre done, you should be sending and receiving your very own fm broadcasts from within the con. Referred to as the baseband signal carrier a higher frequency sinusoid example. Teach the basics of frequency modulation and demodulation national instruments.
A phaselocked loop pll can be used to create a complex but highperformance circuit for fm demodulation. There are many types of modulation so there are many types of demodulators. The pll fm demodulator provides a very attractive option in many instances, offering exceedingly low levels of distortion, and the ability to be incorporated into integrated circuit technology. Once the signal has been received, filtered and amplified, it is necessary to recover the original modulation from the carrier. Mixeramplifier allows fm ip signal to be am modulated by a noise ip prior to demodulation 3. Fm detector demodulators the fm detector demodulator treats the fsk signal as a simple fm signal with binary modulation. The fm demodulator is done with the help of a circuit called phase locked loop pll. Two of them mixed and pll demodulator are are implemented on the dsp tms320c6711dsk.
Downmixing lowpass filtering decimation the multiplication with the square root of two is included to preserve the energy in the signal explained in section 3. Carrier is recovered by the carrier recovery circuit at the receiver. When a modulated signal arrives at the receiving antenna, the embedded information must somehow be extracted by the receiver and separated from the hf carrier signal. An oscillator whose frequency is controlled by its input mt in this manner is called a voltage controlledoscillator. Restoring or recovering the message signal from the received modulated waveform that is generally corrupted by noise types of am detectors.
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