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. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod. Demodulation is extracting the original informationbearing signal from a carrier wave. In many respects the foster seeley fm demodulator resembles the circuit of a full wave bridge rectifier the format that uses a centre tapped transformer, but additional components are added to give it a frequency sensitive aspect. A noncoherent detector has only one input, namely, the modulated signal port. La72912v fm modulator and demodulator ic on semiconductor. The essential parts of the fm demodulation system, which are. 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. As the amplitude variations occurs in the sine wave the frequency generated by the 555 changes and hence a frequency modulated wave is obtained at the output of the 555 ic. All digital fm demodulator kartik nair vtechworks virginia tech. In this experiment, we will consider a simple slope detector circuit for fm demodulation. The pll is examined in the lab sheet entitled fm demodulation by pll. A pll should have basic functional blocks like voltage controlled oscillator vco, phase comparator, low pass. Fm signal will result in a larger signal amplitude at the output of the tuned circuit, and any decrease will result in a smaller amplitude.
The demodulation module involves division and arctan for which there is no dedicated hardware on a fixedpoint dsp. Consider a frequencymodulated signal fed to a tuned circuit whose resonant frequency is to one side of the center frequency of the fm signal. Copy of fm modulation and demodulation circuit multisim live. Then we need a circuit that can add an appropriate dc offset to the. In the modulating process the carrier wave is generated by the lo circuit, and then combined with the baseband signal inside the mixer.
The pulse width demodulation circuit with the first order low pass filter used for the demodulation is given in the following figure. Once the signal has been received, filtered and amplified, it is necessary to recover the. Design and implementation of pll for frequency demodulation. The fm demodulator is done with the help of a circuit called phase locked loop pll. A simple pll fm demodulator circuit using ic xr2212 is shown here. In this paper, pll fm detectors were designed from the pll integrated circuits where the frequency demodulation was obtained directly from the pll circuit by. Its adjustment free modulationdemodulation circuit significantly. Remember to set up the vco module in 100 khz vco mode. To understand the theoretical foundations for angle modulation as well as frequency modulation fm and demodulation.
Aug 29, 20 the fm demodulator is done with the help of a circuit called phase locked loop pll. Implementation of fm demodulator algorithms on a high performance digital signal processor tms320c6711 dsp franz schnyder christoph haller. The foster seeley fm discriminator, detector or demodulator enabled audio to be recovered from frequency modulated signals using a relatively simple circuit. There are different types of modulation and so are demodulators. The mute circuit malfunctions and demodulation output decreases if the voltage level at this pin drops below 180 mv. In an earlier semester project, four fm demodulation algo. Frequency discriminator slope detector phase locked loop.
Implementation of fm demodulator algorithms on a high. Attention each group will submit only one report which will be completed on this experiment document. At this point, an envelope detector such as the one used for. 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. When implemented in q30 representation, the snr is expected to be further increased. The proposed circuit is an alldigital quadrature demodulator, where the individual components. The pll was operated as a complete if strip, limiter, and detector employed in fm receivers.
Slope detector can be constructed with the help of a tuned amplifier and an envelope detector. Using matlab mfile and simulink to implement fm modulation and demodulation. The second section will be the design of the fm radio front end. Introduction frequency modulation is a form of modulation, which represents information as. For this to operate correctly the demodulator circuit between pins 10 and 11 must have a loaded qfactor of 19. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont.
A phaselocked loop pll can be used to create a complex but highperformance circuit for fm demodulation. Implementation of fm demodulator algorithms on a high performance digital signal processor. The demodulated signal might require amplification and. Fm modulation introduction in this lab, you will investigate frequency modulation fm and its properties. The block diagram of a discretetime version of a pll is shown in the. 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. It does this by combining a phase detector, a lowpass filter aka loop filter, and a voltagecontrolled oscillator vco into a negativefeedback system, as follows. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. Slope detector fm demodulation that is illustrated in figure 633. Frequency modulation parts required for lab 6 resistors. Other methods of fm demodulation include a phase locked loop pll demodulator, and various arrangements using tuned circuits once popular, but no longer in these days of miniature, integrated circuit implementations. In an earlier semester project, four fm demodulation algorithms were developed and tested on their suitability. The output of this tuned circuit will have an amplitude that depends on the frequency deviation of the input signal. One approach to reduce this interference, known as frequencydivision multiplexing, allocates different carrier frequencies to different users or for dif.
Heres a simple fm receiver with minimum components for local fm reception. A pll can lock onto the frequency of an incoming waveform. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. Apr 16, 2017 demodulation of fm is done by frequency discrimination method and phase discrimination method. This circuit compensates nonlinearities introduced by demodulation. Xr2212 is a highly stable, monolithic pll phase locked loop ic specifically designed for communication and control system applications. Functions ask modulation and demodulation video signal fm modulation and demodulation. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave. Frequency modulation is widely used for fm radio broadcasting. A pll should have basic functional blocks like voltage controlled oscillator vco, phase comparator, low. There are a number of circuits that can be used to. This is because it is a simple circuit and does not have the power and sensitivity to receive the weak signal. A transistor amplifier is used for additional gain.
The output signal via demodulator may describe the sound, images or binary data. You will model the pll, and recover the message from the fm signal. The coupling and emitter bypass capacitors are chosen as. The la72912v is a fm modulation and demodulation singlechip. Demodulation in this case is simply involves the detection of the envelope of a sinusoid. This method is shown to be effective with respect to speed. An envelope detector is any circuit whose output follows the envelope of an input signal. Demodulation of fm slope and balanced slope detector. Your design decisions, circuit, plots,and expected results. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. The zerocrossingcounter demodulator a simple yet effective fm demodulator is one which takes a time average of the zero crossings of the fm signal.
Abstract this paper addresses the fixedpoint dsp implementation of fm demodulation and decoding for the digital radio application. The njw2307 includes fm modulation demodulation, vco, pll and afc, will contribute to the adjustmentfree. The design approach is to design the fm demodulator as if it were an analog phase lock loop. Construct the circuit shown in figure 2 using 91 k. I got the idea for this circuit from one of my professors. Otherwise, you wont receive the commercial broadcast signal. Fixedpoint dsp implementation of fm demodulationdecoding. The signal output from a demodulator may represent sound an. Fm demodulation is a key process in the reception of a frequency modulated signal.
Lm565lm565c phase locked loop general description the lm565 and lm565c are general purpose phase locked loops containing a stable, highly linear voltage controlled oscillator for low distortion fm demodulation, and a double balanced phase detector with good carrier suppression. There are a number of circuits that can be used to demodulate. Division is normally achieved either by using the newtonraphson method or by. Its adjustment free modulationdemodulation circuit significantly reduces the number of peripheral circuits required and can contribute to lower production costs. It is also used in telemetry, radar, seismic prospecting, and monitoring newborns for seizures via eeg, twoway radio systems, music synthesis, magnetic tape. Transistor bf495 t2, together with a 10k resistor r1, coil l, 22pf variable capacitor vc, and internal capacitances of transistor bf494 t1, comprises the colpitts oscillator the resonance frequency of this oscillator is set by trimmer vc to the frequency of the transmitting station that we wish to listen. Fm modulationdemodulation with pll general description package outline njw2307 is a fm modulation demodulation ic for audio signal in full duplex communication that operates from 3. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. Pdf design of a digital fm demodulator based on a 2ndorder all. Demodulate fm signal using fm to am conversion discriminator. Overview of fm demodulation to recover the message mt. Consequently there is no need for the demodulator tuned circuit to be adjusted for minimum thd, instead the adjustment criterium is for a symmetrical stop pulse.
However, you can construct any fm transmitter circuit which works in the fm band 88108 mhz and receive the transmitted signal using this simple fm receiver circuit. Refer to the circuit diagram in figure 76 or figure acs72 on etek acs300004 module to produce the demodulated fm signal as the signal source. Function internal equivalent circuit notes 10 if input if input via the phase shift circuit. In any radio that is designed to receive frequency modulated signals there is some form of fm demodulator or detector. Theory frequency demodulator is a circuit which converts instantaneous frequency variations to linear.
There are many types of modulation so there are many types of demodulators. It simply uses a tuned circuit that is tuned to a frequency slightly offset from the carrier of the signal. Frequency modulation fm is a process in which the carrier frequency is varied. Slope detector fm demodulation balanced slope detector.
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. As the frequency of the signal varies up and down in frequency according to its modulation, so the signal moves up and down the slope of the tuned circuit. That design wasnt meant for passing frequencies high enough to be able to pass an audio file, e. January 22, 2019 january 25, 2019 by ian etheridge 2 comments. Nov 11, 2018 consider a frequency modulated signal fed to a tuned circuit whose resonant frequency is to one side of the center frequency of the fm signal. If your signal is narrow band, a few khz or so you could get by with an if of less than 500 khz which is the maximum frequency for the lm565s oscillator. It is also used in telemetry, radar, seismic prospecting, and monitoring newborns for seizures via eeg. Monolithic linear ic la1145, 1145m fm if system quadrature. Fmif amplifierdemodulator circuit nxp semiconductors.
Lm565lm565c phase locked loop michigan state university. Need a circuit whose output is proportional to the difference of the instantaneous frequency from the carrier frequency. Using a phaselockedloopfor fm demodulation a device called a phaselockedlooppll can be used to demodulate an fm signal with better performance in a noisy environment than a frequency discriminator. In addition to audio signal, it can also be used in data pulse. 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.
If the receiver uses a pll to demodulate the fm, it would likely be at the intermediate frequency if. Demodulation of fm is done by frequency discrimination method and phase discrimination method. Circuit diagram of pulse width demodulation circuit with low pass filter. It uses a phase shift circuit it converts the instantaneous frequency deviation in an fm signal to phase shift and then detects the changes of phase cs results in 90 deg. The very simplest form of fm demodulation is known as slope detection or demodulation. The vco frequency is set with an external resistor and capacitor. Consider a frequency modulated signal fed to a tuned circuit whose resonant frequency is to one side of the center frequency of the fm signal. The continuous analog signal st is a baseband signal with the information content. A pll should have basic functional blocks like voltage controlled oscillator vco, phase comparator, low pass filter lpf and source follower. Fm receiver electronics circuit with full explanation. Modulation and demodulation medium, it would be dif.