Pulse width modulation is also referred
to as pulse duration or pulse length modulation and
along with pulse position modulation, may be termed
as a form of pulse time or pulse frequency modulation.
In PWM systems, the leading edge, the trailing edge
or both may be varied as a function of the amplitude
of the sampled signal, and care must be taken to ensure
that the pulses do not overlap in a TDM system. In general,
PWM requires a greater average power than PAM systems.
Also, the PWM system requires a larger bandwidth than
PAM.
If there are K signals to be multiplexed and if  is
the highest frequency in these signals, then the maximum
permissible pulse width without overlapping is given
by  seconds. |
,
the pulse width will 
and
the modulated pulse-train is given as below:
( as 
)