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FSK MODULATORMahin Khushbakht atiq (08-TE-03)Tayaba Irum (08-TE-06)Javeria Yasmin (08-TE-15)Qurrat-ul-ain (08-TE-21)Samreen Kousar (08-TE-50)Kinza Ahmed (08-TE-56)

Outline:Digital ModulationFrequency shift keyingFSK ModulatorFSK modulator specificationsDesign configurationSimulink Implementation

Digital modulation can then be defined as the process whereby the amplitude, frequency, phase or a combination of them is varied in accordance with the information to be transmitted. digital data (0 and 1) is translated into an analog signal --- the baseband signal.

Digital modulation:

Digital modulation is used before analog modulation to convert the digital data into analog baseband signal.

The move to digital modulation provides:more information capacitycompatibility with digital data serviceshigher data securitybetter quality communicationsquicker system availability. Developers of communications systems face these constraints: available bandwidth permissible power inherent noise level of the system Why digital modulation?The RF spectrum must be shared, yet every day there are more users for that spectrum as demand for communications services increases. Digital modulation schemes have greater capacity to convey large amounts of information than analog modulation schemes. Cont.We can vary each of these parameters or a combination of these parameters to represent our information signal.The basic sine signal:

A scheme that uses: amplitude is called ASK (Amplitude Shift Keying) frequency is called FSK (Frequency Shift Keying) phase is called PSK (Phase Shift Keying) Types of digital modulation:

Frequency-shift keying (FSK)is afrequency modulation scheme in which digital information is transmitted through discrete frequency changes of acarrier wave. The simplest FSK isbinaryFSK(BFSK).

Frequency shift keying: FSK

BFSK signal:

Data rate 4800, 9600, 14400 BPSCarrier frequency f0 = 2.4 GHz, f1 = 2.5 GHzInput signaling RS 232C serial communication.Modulation method - FSK

FSK modulator specsFSK Modulator Design The relation of FSK signal and data signal is shown in figure .

When the data signal is 5 V, after the signal pass through the buffer, the switch S1 will ON, then the frequency of FSK signal is f1.

When the data signal is 0 V, after the signal pass through the buffer, the switch S2 will ON, the frequency of FSK signal is f2.

Normally, the difference between frequencies f1 and f2 has to be as large as possible. This is because the correlation of both signals is low, therefore, the effect of transmitting and receiving will be better. However, the required bandwidth must be increased. Figure is the signal waveforms of FSK modulation.

Structure diagram of FSK modulator. DIGITAL DATAFSK signalPOWER SUPPLY (+5V)VCO (SBVD-10D)RS232 C INTERFACE (MAX3232)ATTENUATORCLIPPER (1N4148)CONNECTOR (9PIN DSUB, SMA (F, R-ANGLE))PARTS SPECIFICATIONS:We are using MAX3232 for RS232 to TTL voltage level conversion. The TTL level is a logic 1for any voltage above about 1.5 volts and a logic 0 for any voltage below about 1.5 volts.

RS232C INTERFACE

TTL= transistor- transistor logic, 17Aclipperis a device designed to prevent the output of a circuit from exceeding a predetermined voltage level without distorting the remaining part of the applied waveform.A clipping circuit consists of linear elements likeresistors and non-linear elements likejunction diodesortransistors, but it does not contain energy-storage elements likecapacitors. Clipping circuits are used to select for purposes of transmission, that part of a signal wave form which lies above or below a certain reference voltage level.Used to create a voltage level at which the VCO operates. clipper18

Two shunt diode clipper circuitsIn the example circuits above, one or twoZener diodesare used to clip the voltage VIN. In the first circuit, the voltage is clipped to the reverse breakdown voltage of the zener diode. The output voltage in the first circuit should also never be more negative than the diode's forward voltage (such as .7V for a typical diode), but it is not shown in the picture. In the second, the voltage in either direction is limited to the reverse breakdown voltageplusthe voltage drop across one zener diode.

19Avoltage-controlled oscillatororVCOis anelectronic oscillatordesigned to be controlled inoscillationfrequencyby avoltageinput. The frequency of oscillation is varied by the applied DC voltage, whilemodulatingsignals may also be fed into the VCO to cause Frequency shift keying. voltage-controlled oscillator

Anattenuatoris anelectronic devicethat reduces theamplitudeorpowerof asignalwithout appreciablydistortingitswaveform. Filters are used as attenuator allowing the required frequencies to pass and prohibiting others.

ATTENUATOR SIMULINK MODEL If we divide the whole model into different small modules than it consists of: Binary generatorFSK modulatorChannelDescriptionModel:

This is the complete simulink model for the FSK modultor. 24

the input is binary zeros and ones randomly generated by the Bernoulli binary generator. Lets now come to the first block FSK modulator and see whats inside.25FSK modulator

This the background circuitry of the FSK modulator, here two frequency carriers at 2.5 GHz and 2.4 GHz and the binary stream are input into the FSK modulator. The two scopes show the two carrier frequencies. 26Scope 2Scope 1

The switch uses is controlled by the binary input and it selects f1 for a binary 1 and selects f2 for a binary 0. 29

This the final output of the FSK modulator.30Channel

The channel adds Band-limited white noise. White noiseis a randomsignal(or process) with a flatpower spectral density. In other words, the signal contains equal power within a fixedbandwidthat any center frequency.32

The upper signal represents the output after passing through the channel and the lower signal is the white noise.33Final output of the system:

FSK modulators are used practically in telecom applications to transmit the information signals to longer distances using frequency in Giga hertz ranges but the noise addition is the main constraint in this process. Point to point military communicationMost early telephone-linemodemsused audio frequency-shift keying to send and receive data, up to rates of about 1200 bits per second.FSK is also used in the Emergency Alert Systemto transmit warning information.Applications:Military communication because of its inherit security property, as exactly same carrier frequencies should be generated at the receiver to demod the signal.35We have discussed so for the overall system of FSK modulator with Basic FSK modulator theoryDesign specificationDesign configurationSimulink Model DesignApplication

SummaryTHANK YOU