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 Pulse Modulation Digital Pulse Modulation
Pulse Amplitude (PAM)
Pulse Width (PWM)
Pulse Code (PCM)
Delta (DM)
Pulse Modulation
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 as PAM.

5. Pulse Amplitude Modulation (PAM)

6. PAM Generator

7. Wave form of PAM

8. Advantages of PAM
Generation and detection is easy.
Disadvantages of PAM
Added noise cannot be removed easily as it has impact on
amplitude which carries information.
Transmission bandwidth is too large.

9. Pulse Width/ Duration/Length Modulation
(PWM or PLM or PDM)
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 as PWM.

10. Pulse Width Modulation (PWM)

11. PWM Generator

12. PWM Waveform

13. Advantages of PWM
1. Very good noise immunity.
2. Its possible to separate out signal from noise.
Disadvantages of PWM
1. Bandwidth requirement is large as compared to PAM.

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 as PPM.

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 analog signal.
*PPM signal is further modification of a PWM 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 a pulse.
* This wave can be
further amended
by eliminating the
whole positive
narrow pulses.
The remaining
pulse is called
clipped PPM.
PWM
PPM
Pulse Position Modulation (PPM):

17. PPM Generator

18. Advantage of PPM
 High noise immunity.
Disadvantage of PPM
 Generation and detection is complex.

19. PAM, PWM and PPM at a glance:
Analog Signal
Amplitude Modulated Pulses
Width Modulated Pulses
Position Modulated Pulses

20. Basis for
Comparison
PAM PWM PPM
Varying parameter Amplitude Width Position
Immunity towards
noise
Low High High
Signal to noise ratio Low Moderate Comparitively high
Need of
synchronization pulse
Not exist Not exist Exist
Bandwidth
dependency
On pulse width On rise time of pulse On rise time of pulse
Transmission power Variable 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)
 It is the type of pulse modulation in
which the group of pulses or codes are
transmitted which represent binary
numbers corresponding to modulating
signal voltage.

22. * Analog signal is converted into digital signal by using a digital
code.
* Analog to digital converter employs two techniques:
1.Sampling: The process of generating pulses of zero width
and of amplitude equal to the instantaneous amplitude of the
analog signal. The no. of pulses per second is called
“sampling rate”.
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 Binary Code.
The levels obtained are called “quanization levels”.
* A digital signal is described by its „bit rate‟ whereas analog
signal is described by its „frequency range‟.
* Bit rate = sampling rate x no. of bits / sample
Pulse Code Modulation (PCM):

23. Time
l
t
111
110
101
100
011
010
001
000
7
L 6
e 5
v 4
e 3
l 2
s 1
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 and Coding

24. PCM

25. Advantages of PCM
1. Secured.
2. Encoding is possible.
3. Very high noise immunity.
4. Convenient for long distance communication.
5. Good signal to noise ratio.
Disadvantages of PCM
1. Complex circuitry.
2. Requires large bandwidth.
3. Synchronization is required between transmitter &
receiver.

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

27. Concept of DM

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

29. Demodulation
• Demodulation is digital-to-analog signal conversion.
• It’s the reverse System of modulation.
• Demodulation was first used in radio receivers.

30. De M Block Diagram

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

32. Advantages of DM
1. One bit code word for output.
2. Low signaling rate.
3. Low channel bandwidth.
• Disadvantages of DM
1. Slope overload present.
2. Granular noise present.

33. PCM VS DM