modullation ppt new

Modulation & Its Types Presented By-

P.L.Rongmei Manoj Kumar

(ME-IST YR, I&C)

• Electrical Engineering Deptt NITTTR, Chandigarh

1. Communication: Processing, sending and receiving of information

Source of information

Transmitter

Link

Receiver Destination

i) Speech ii) Pictures iii) Words iv) Codes v) Symbols vi) Commands vii) Data

i) Oscillators ii) Amplifiers iii) Filters iv) Antenna

i) Wire Links ii) Wireless iii) Optic Fibres

i) Radio ii) TV iii) Computer iv) Telephone v) Teleprinter vi) Telegraph vii) Fax viii) Internet

BASICS OF COMMUNICATION1. Communication: Processing, sending and receiving of information

2. Information: Intelligence, signal, data or any measurable physical quantity

3. Basic Communication System:

Forms of Communication:

1. Radio Broadcast

2. Television Broadcast

3. Telephony

4. Telegraphy

5. Radar

6. Sonar

7. Fax (Facsimile Telegraphy)

8. E-mail

9. Teleprinting

10. Telemetering

11. Mobile Phones

12. Internet

Types of communication:

1. Cable communication

2. Ground wave communication

3. Sky wave communication

4. Satellite communication

5. Optic fibre communication

Analogue signal

A continuous signal value which at any instant lies within the range of a maximum and a minimum value.

A discontinuous signal value which appears in steps in pre-determined levels rather than having the continuous change.

Digital signal

0 t

V1 0 1 0 1 0 1 0 1

T/4 T/2 3T/4 T 5T/4 3T/2 7T/4 2Tt

0π 2π 3π 4ππ/2 3π/2 5π/2 7π/2 θ = ωt

E ,I E0

E = E0 sin ωtI = I0 sin ωt

I0

MODULATION:Modulation is the process of variation of some characteristic of a high frequency wave (carrier wave) in accordance with the instantaneous value of a modulating signal.

NEED FOR MODULATION:

1) TO REDUCE THE ANTENNA HEIGHT

2) TO MULTIPLEX THE MORE NUMBER OF SIGNALS

3) TO NARROW BANDING THE SIGNAL

4) TO REDUCE EQUIPMENT COMPLEXITY

Height of Antenna = 1/4 wavelength and, wavelength = velocity of light / frequencyrange of audio frequency = (20 - 20k)hz.

Types of Modulation:

1. Amplitude Modulation

2. Frequency Modulation

3. Phase Modulation

AMPLITUDE MODULATION:

Modulator

A.F. Signal Amplitude

Modulated Signal

H.F. Signal Oscillator

AMPLITUDE MODULATION (AM):

e m= Em sin mt

ec = Ec sin ct

e = EAM sin

Amplitude modulation of a sine or cosine carrier results in a variation of the carrier amplitude that is proportional to the amplitude of the modulating signal.

Where,

e m= modulating signal

e c = carrier signal

e = modulated signal

AMPLITUDE MODULATION (AM):

Here,

EAM = EC+eM

e = EAM sin

e = (EC+eM ) sin

e = (Ec + Em sin mt) sin ct

Where,

EAM = Amplitude of Modulated signal

sin = sin ct

AMPLITUDE MODULATION (AM):

From the above expression,

ma =Modulation Index; ma = kaEm/Ec

ka = amplitude sensitivity

If ka=1, then ma= Em/Ec

e = Ec sin ct + (maEc/2) cos (c - m)t

- (maEc/2) cos (c + m)t

1. The Amplitude Modulated wave is the summation of three sinusoidal waves with different frequencies c, c- m and c+ m namely Original frequency, Lower Side Band frequency and Upper Side Band frequency respectively.

2. The Bandwidth required for AM, BW = 2 m

3. The amplitude Ec of the unmodulated carrier wave is made proportional to the instantaneous voltage (e m = Em sin mt) of the modulating wave.

Voltage Amplitude

Frequency

Inferences from equation for e:

c- m c c+ m

Significance of Modulation Index:

maEc= kaEm

Emin

Emaxe

0

Emax = Ec + maEc

Emin = Ec - maEc

Emax - Emin

Emax + Emin

ma =

Generally,

0 < ma < 1

AF signal

ma = 0 (No modulation)

ma = 0.5 or 50%

On manipulating, we get

ma = 1 or 100%

ma > 1 or 100%

Ec

Power Relation in the AM wave:

If the modulated wave is applied to a resistor of resistance R (say antenna circuit), then the r.m.s. power dissipated in the form of heat is,

Pr.m.s = (1/R)Ec /22 + maEc /222 + maEc /222

Prms = (Ec 2 /2R) 1 + (ma

2 /2) = Pc1 + (ma2 /2)

(where Pc is power dissipated by unmodulated carrier wave)

If ma = 1, then Prms Pmax and Pmax = 3 Pc /2

Similarly, Power carried by both side bands PSB = Prms / 3 which is wasted.

Generation of AM Waves

Consider, two devices used for the generation of AM waves:

1. The square Law Modulator2. The Switching Modulator

Square Law Modulator:

Required Three features:1. Summing (Carrier and Modulating)2. Non Linear Element3. Band Pass Filter

Fig. Square-Law Modulation

Square Law ModulatorThe output v1(t) of the Non-Linear Element is given by;

v2(t) = a1 v1(t) + a2 v12(t) (by Square-Law)

Where, a1 and a2 are constants.

Input signal to non-linear element, v1(t) = Ac cos(2fct) + m(t)

From the above two equation,v2(t) = a1Ac[1+(2a2/a1)m(t)]cos(2fct) +

a1m(t) + a2m2(t) + a2(Ac)2cos2(2fct).

the first term is the desire AM wave with amplitude sensitivity ka = 2a2/a1. the remaining three terms are unwanted terms that are removed by filtering.

Switching Modulator:

Consider the arrangements of switching modulator as shown in fig. it is used for carrier wave c(t) is greater than m(t) in amplitude.

Switching Modulator:

V1(t) = Accos(2fct) + m(t)

Where m(t) << Ac the resulting load voltage V2(t) is

V2(t) = V1(t), c(t) > 0

= 0 , c(t) < 0The load voltage V2(t) varies periodically between the value V1(t) & 0 at a rate equal to the carrier frequency fc

DemodulationIt is reverse process of Modulation.The devices used for Demodulation are;

1. Square-Law Detector2. Envelope Detector

Square-Law Detector

• It is essentially obtained by using a Square-Law Modulator for the purpose of Demodulation.

• By square-Law, determination of transfer characteristic of a non-linear device is given by,

v2(t) = a1 v1(t) + a2 v12(t) …(1)

• The input of the device will be, v1(t) = Ac[ 1+kam(t)]cos(2fct) … (2)

From the above two equations, the desired is, Ac

2kam(t)Which is obtained from the term a2 v1

2(t) as explained in equation (1).

Envelope Detector• An envelope detector produced an output

signal that follows the envelope of input signal waveform exactly.

• The circuit diagram of envelope detector is given below:

Working of Envelope Detector

• Requirement:

-- Narrow band of AM wave(fc>>fm).

-- Percentage of modulation is less than 100%.

Contd.. (Working of Envelope Detector)

AM signal R C

tt

t

+

vc(t)

-

Rs

Contd.. (Working of Envelope Detector)

• Necessary condition;-- The diode should be ideal.-- The charging time constant should be RsC<<1/fc

--The discharging time constant RLC ranges as:

1/fc << RLC<<1/W .

Where, W – Message bandwidth. fc-carrier frequency.

DSB-SC Modulation

• A fraction of total power transmitted is affected by the m(t) and the rest of the power is because of information carrying signal.

• We may suppress the carrier component from the modulated wave.

• By suppressing the carrier wave, we obtain a modulated wave that is proportional to the product of the carrier wave and the baseband signal.

• Therefore, s(t) = Ac cos(2fct) m(t).

Generation of DSBSC wave

The device for achieving the requirement of the DSBSC modulated wave is called “ product modulator”. The device can be described in two forms:

(1) Balance modulator(2) Ring modulator

Balanced Modulator

To suppress the carrier wave, two AM modulators are used as shown in block diagram

Contd… Balanced Modulator

Condition to be satisfied:• Both the Modulators should be identical.• One of the m(t) applied to the modulators should be

opposite in polarity (-m(t).Then, the output of the modulators are;

s1(t) = Ac[ 1+kam(t)]cos(2fct) and

s2(t) = Ac[ 1- kam(t)]cos(2fct)

Subtracting s2(t) from s1(t), we get

s (t) = 2ka Ac cos(2fct) m(t)

Ring Modulator

The Ring Modulator circuit consist of ;• Four Diodes• Two Transformers

Generation of DSBSC wave

Ring Modulator

Diode switching modes:

( a) (b)

Ring Modulator

DSBSC Waves Detector

There are three Detectors of DSBSC Waves:

1. Coherent Detector2. Costas Receiver3. Squaring Loop

Coherent Detector

• This method of demodulation is also known as “Synchronous Detector”.

• The block diagram of the detector is shown below;

v(t)=Ac cos (2fct + ) s(t) and

vo(t)= Ac Ac ‘ cos m(t)

SSB Modulation• In Amplitude Modulation including DSBSC

Modulation, the transmission bandwidth is double the message bandwidth (uper-sideband and lower-sideband).

• Both the sidebands are carrying same information.

• One of the sideband can be suppressed without any lost of information.

• This system is known as Single Sideband (SSB) system.

SSB ModulationDifferent Spectrums are shown below;

• Spectrum of Baseband signal

• Spectrum of DSBSC wave.

• Spectrum of SSB wave with upper-sideband transmitted

• Spectrum of SSB wave with lower-sideband transmitted

Generation of SSB

There are two method of Generation of SSB waves:1. Frequency Discrimination Method2. Phase discrimination Method

The block diagram of “frequency discrimination “method (single stage) for generating SSB wave is shown in below;

Demodulation of SSB waves

SSB waves Demodulation block diagram is shown in fig. below;

Vestigial Sideband Modulation

• In VSB system one sideband and a vestige of other sideband are transmitted together.

• The resulting signal has a bandwidth > the bandwidth of the modulating (baseband) signal but < the DSB signal bandwidth.

• If the baseband signal contains significant components at extremely low frequencies, which may not be present in both the sidebands.

• The above condition the SSB is inappropriate.

Vestigial Sideband Modulation

Spectrum of Baseband Signal

Spectrum of VSB Wave

Block diagram of VSB:

Angle modulation

• There are two forms of angle modulation phase modulation & frequency modulation detail of the angle modulation given below. Let the angle modulation wave is s(t)= Ac cos[ϴi(t)]…………………..(1) where Ac -is Carrier amplitude, ϴi(t )= Angle of a modulated sinusoidal career

• a complete oscillation occurs whenever ϴi(t) changes by 2π radians.

Continued……….• The angle ϴi(t) may be varied in some manner with the base band

signal. Consider Only two methods. (1) phase modulation (2) frequency modulation

• Phase modulation- phase modulation is defined as the process in which the phase of the carrier wave is varied in accordance with a message signal or the baseband signal. in phase modulation Amplitude & frequency are constant.

OR in which the angle ϴi(t) is varied linearly with the message signal m(t).

ϴi(t )= 2πfc t+ kp m(t)………………(1) where 2πfc t – angle of the un modulated career. kp = phase sensitivty of the modulator in radian/volt

The phase modulated wave s(t) is s(t) =Ac Cos [2πfc t + kp m(t) ]……………………………..(2)

1. AM is an easier method of transmitting and receiving speech signals.

2. It requires simple and inexpensive receivers.

3. It is a fairly efficient system of modulation.

Drawbacks:4. AM is more likely to suffer from noise.

2. Appreciable energy is contained by three components of AM wave. Sufficient energy can be saved by suppressing carrier wave and one of the side bands. This process makes the equipment complex.

3. Cost of such transmitters and receivers becomes practically more.

Advantages:

Phase modulation

Wave forms of phase modulation.

Wave forms of phase modulation

Block Diag. Of Phase Modulation

Frequency Modulation

• Frequency modulation is defined as the process in which the Frequency of the carrier wave is varied in accordance with a message signal or the baseband signal .in Frequency modulation Amplitude & phase are constant.

ORFrequency modulation (FM) is that form of angle modulation in

which the instantaneous frequency fi(t) is varied linearly with the base band signal m(t) as shown by

fi(t)= fc + kf m(t)……………………………………….(1)

where- fc ……… frequency of the unmodulated carrier,

FM Continued…………………

integrating equ.(1) Wave shape…………

Types of frequency modulation

• Block diag of method of generating a narrow band FM signal.

Integrator ƩNarrow band

FM Wave

Modulating Wave Product

Modulator

90o - phase shifter

Carrier waveAccos(2pfct)

Acsin(2pfct)

Fig: Block diagram of a method for generating a Narrow band Modulator

Narrow band Modulator

Types of frequency modulation

• Wide band frequency modulation.• Wide band frequency modulation is analysed

with the Bessel Function of the first kind and argument β for which β will be large and the value of β is given by;

β =∆f/fm

β= modulation index.

Generation of FM

• There are essentially two methods of generating frequency- modulated signals.

(1)Indirect FM(2) Direct FM

• Indirect FM- in this method the instantaneous frequency of the carrier wave is not varied directly in accordance with the message s/g. This method also called ARMSTRONG Freq. Modulation Method.

• For this method β kept small. For minimize the distortion.

• S(t) = Ac Cos[ 2pfc t + βsin(2pfmt)]

• Β = n β1

Generation of FM

Generation of FM

• Indirect FM- this method is explain with the help of block diagram.

fig.:- block diag of indirect method

IntegratorFrequencyMultiplier

Narrow-band phase

modulator

Fixedoscillator

FM SignalBase band

Signal

Generation of FM

oDirect FM method –in this method instantaneous frequency of the carrier wave is varied directly in accordance with the message s/g. By means of a device known as a voltage controlled oscillator.

o Hartley oscillator used.o frequency of oscillation of Hartley oscillator is fi(t) =1/2π{(L1 +L2)C(t)}1/2

un modulated frequency fo= 1/2π{ Co (L1 +L2)} 1/2

Generation of FM

• Direct FM

Block Diag. of wide-band frequency modulator using a voltage-controlled oscillator

m(t) VoltageControlledoscillator

FrequencyMultiplier

FrequencyMultiplierMixer

Band passFilter

Wide-bandFM Wave

Fixedoscillator

Demodulation of FM

• Frequency demodulation is the process that enables to recover the original modulating signal.There are two methods for demodulation:1. Frequency discriminator method2. Phase-Locked Looped Demodulator

1. Block diagram of Frequency discriminator method:-

Frequency discriminator

Wave shape:

fc-BT/2 fc+BT/2

-fc-BT/2 - fc+BT/2

-BT/2 0 +BT/2 Slope= -2πa

Slope=2πa

f

f

Ĥ1(f)/j

H2(f)/j

fc-BT/2 fc+BT/2

-fc-BT/2 - fc+BT/2

Slope=2πa

f

H1(f)/j

0

0

Demodulation of FM

2. Phase- locked loop demodulator:-

FM wave e(t) v(t)

r(t)

(Block diagram of phase locked loop)

Loop Filter

Voltage controlled oscillator

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