Pulse-amplitude modulation, acronym PAM, is a form of
signal modulation where the message information is
encoded in the amplitude of a series of signal pulses.
Example: A two bit modulator (PAM-4) will take two bits at a
time and will map the signal amplitude to one of four
possible levels, for example −3 volts, −1 volt, 1 volt, and 3
Demodulation is performed by detecting the amplitude
level of the carrier at every symbol period.
Pulse-amplitude modulation is widely used in baseband
transmission of digital data, with non-baseband
applications having been largely superseded by pulsecode modulation, and, more recently, by pulse-position
Analog pulse modulation
Digital pulse modulation
In the pulse amplitude modulation of pulsed carrier
is changed in proportion with the instantaneous
amplitude of the modulating signal x(t). So the
information is continued in the amplitude variation of
the carrier is in the form of train of narrow pulses .
If you compare the PAM system with the sampling
process ,you will find these two processes are
The PAM signal is then sent by either wire or cable or
it is used to modulate a carrier.
Generation of natural PAM
The PAM signal can be detected
(demodulated) by passing it through a low
The low pass filter cutoff frequency is
adjusted to fm so that all the high frequency
ripple is removed and the original modulating
signal is recovered back.
Due to the aperture effect an amplitude
This distortion can be corrected by equalizer
Better SNR due to increased signal power.
Generation is easy.
Aperture effect introduces distortion.
Flat top PAM
Nature of sampling
Train of finite duration
Train of finite duration pulses
Circuit arrangement Uses a chopper
Uses a sample n hold circuit
Increases with increase in
the pulse width
Increases with increase in the
Increases with the
reduction in pulse width
Increases with reduction in
the pulse width
Effect of noise
Since the information is contained in the amplitude
variations, the noise will contaminate the information
Q. Explain generation and demodulation of PAM
signal with the help of suitable diagrams.
(10 marks-May 2008)