Pulse modulation, Pulse Amplitude (PAM), Pulse Width (PWM/PLM/PDM), Pulse Position (PPM), Pulse Code (PCM), Delta (DM)

Pulse Amplitude (PAM)
Pulse Width (PWM/PLM/PDM)
Pulse Position (PPM)
Comparison of PAM, PWM and PPM

Pulse Code (PCM)
Delta (DM)
Comparison of DM and PCM

1. Topics
•Pulse Amplitude(PAM)
•Pulse Width(PWM/PLM/PDM)
•Pulse Position(PPM)
•Comparison of PAM, PWM and PPM
•Pulse Code(PCM)
•Delta(DM)
•Comparison of DM and PCM

2. Modulation

3. Analog PulseModulation Digital PulseModulation
Pulse Amplitude(PAM)
Pulse Width(PWM)
Pulse Code(PCM)
Delta(DM)
PulseModulation
Pulse Position(PPM)

4. Pulse Amplitude Modulation (PAM)
A modulation system in which amplitude of
discrete carrier signal changes in accordance with
the instantaneous amplitude of modulating
signal(message signal) keeping width and position
of carrier constant is called asPAM.

5. Pulse Amplitude Modulation (PAM)

6. PAMGenerator

7. Wave form ofPAM

8. Advantages of PAM
Generation and detection iseasy.
Disadvantages of PAM
Added noise cannot be removed easily as it has impacton
amplitude which carriesinformation.
Transmission bandwidth is toolarge.

9. Pulse Width/Duration/LengthModulation
(PWM or PLM orPDM)
The modulation system in which width of the
discrete carrier signal changes in accordance with
the instantaneous amplitude of modulating
signal(message signal) keeping amplitude and
position of carrier constant is called asPWM.

10. Pulse Width Modulation(PWM)

11. PWMGenerator

12. PWMWaveform

13. Advantages ofPWM
1.Very good noiseimmunity.
2.Its possible to separate out signal fromnoise.
Disadvantages ofPWM
1.Bandwidth requirement is large as compared toPAM.

14. Pulse Position Modulation (PPM)
The modulation system in which position of
the discrete carrier signal changes in
accordance with the instantaneous
amplitude of modulating signal(message
signal) keeping amplitude and Width of
carrier constant is called asPPM.

15. Pulse Position Modulation (PPM)

16. *In this type, the sampled waveform has fixed amplitude and
width whereas the position of each pulse is varied as per
instantaneous value of the analogsignal.
*PPM signal is further modification of aPWM signal.It has
positive thin pulses (zero time or width) corresponding to the
starting edge of a PWM pulse and negative thin pulses
corresponding to the ending edge of apulse.
*This wave canbe
further amended
by eliminating the
whole positive
narrow pulses.
Theremaining
pulseiscalled
clippedPPM.
PWM
PPM
PulsePositionModulation (PPM):

17. PPMGenerator

18. Advantage ofPPM
High noiseimmunity.
DisadvantageofPPM
Generation and detection iscomplex.

19. PAM, PWM and PPM at aglance:
AnalogSignal
Amplitude ModulatedPulses
Width ModulatedPulses
Position ModulatedPulses

20. Basis for
Comparison
PAM PWM PPM
Varying parameterAmplitude Width Position
Immunity towards
noise
Low High High
Signal to noise ratioLow Moderate Comparitivelyhigh
Need of
synchronization pulse
Not exist Not exist Exist
Bandwidth
dependency
On pulse width On rise time of pulseOn rise time of pulse
Transmission powerVariable Variable Constant
Bandwidth
requirement
Low High High
Similarity of
implementation
Similar to AM Similar to FM Similar to PM
Synchronization
between Transmitter
and Receiver
Not needed Not needed Needed

21. Pulse Code Modulation(PCM)
Itis the type of pulse modulation in
which the group of pulses or codes are
transmitted which represent binary
numbers corresponding tomodulating
signalvoltage.

22. *Analog signal is converted into digital signal by using a digital
code.
*Analog to digital converter employs twotechniques:
1.Sampling:The process of generating pulses of zero width
and of amplitude equal to the instantaneous amplitude of the
analogsignal.The no. of pulses per second is called
“samplingrate”.
2.Quantization:The process of dividing the maximum value
of the analog signal into a fixed no. of levels in order to
convert the PAM into a BinaryCode.
The levels obtained are called “quanizationlevels”.
*A digital signal is described by its „bit rate‟ whereas analog
signal is described by its „frequencyrange‟.
*Bit rate = sampling rate x no. of bits /sample
PulseCodeModulation(PCM):

23. Time
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111
110
101
100
011
010
001
000
7
L
6
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v4
e3
l2
s1
0
B
i
n
a
r
y
C
o
d
e
s
Time
Time
l
t
0 1 0 1 0 1 1 1 0 1 1 1 1 1 0 1 0 1 0 1 0
Sampling, Quantization andCoding

24. PCM

25. Advantages ofPCM
1.Secured.
2.Encoding ispossible.
3.Very high noiseimmunity.
4.Convenient for long distance communication.
5.Good signal to noiseratio.
Disadvantages ofPCM
1.Complexcircuitry.
2.Requires largebandwidth.
3.Synchronization is required between transmitter &
receiver.

26. DeltaModulation
•DM is the simplest form of differential pulse-
code modulation.(PCM)
•To achieve high signal-to-noise ratio, delta
modulation.
•DM can change instantlybut
voice signals can’t not changeinstantly.
•DM signal is smaller than the PCMsystem.
Delta Modulation used by Satellite Business
Systems orSBS.

27. Concept ofDM

28. DM BlockDiagram
•If signal is large, the next bit in the digital data is 1,
otherwise, it is O.

29. Demodulation
•Demodulation is digital-to-analog signalconversion.
•It’s the reverse System ofmodulation.
•Demodulation was first used in radioreceivers.

30. DeMBlockDiagram

31. Limitations of thesystem
•
•
•Slopeoverload
•When the analog signal has a high rate of
change, the DM can “fall behind” and a distorted
output occurs

32. Advantages ofDM
1.One bit code word foroutput.
2.Low signalingrate.
3.Low channelbandwidth.
•Disadvantages ofDM
1.Slope overloadpresent.
2.Granular noisepresent.

33. PCM VSDM