Pulse Width Modulation_555

To study and draw the characteristics of Pulse Width Modulation.


Pulse Width Modulation is widely used in communication system. It is a process in which analog signals are converted to digital form. The analog signal is represented by a series of pulses and non-pulses (1 or 0 respectively).
Also Pulse Width Modulation is one of the powerful technique uses in control systems. It is employed in wide range of control application which includes speed control, power control and measurement.

Pulse Width Modulation

In layman language, Pulse width Modulation is a technique in which you vary the ratio of HIGH time to LOW time of a pulse.
PWM is achieved with the help of a square wave whose Duty Cycle is changed to get a varying voltage output as a result of average value of waveform. This method is sometimes called Pulsed Duration Modulation (PDM) or Pulse Length Modulation (PLM). PWM is an active portion of the duty cycle which is proportional to the amplitude of the analog signal. PWM uses pulse that all have same amplitude. The width of each pulse in a train is made proportional to the instantaneous value of the modulating signal at the instant of the pulse. The duration of each pulse depends on the amplitude of the signal at the time it is sampled.

Duty Cycle :- A duty cycle is the time that an entity spends in an active states as a fraction of t he total time under consideration.
In a periodic event, the duty cycle is the ratio of the duration of the event to the total period of signal.

Where τ is the duration that the function active, and T the period of the function.
In an ideal pulse train (one having rectangular pulses) the duty cycle is the pulse duration divided by the pulse period. For example a pulse train in which pulse duration is 1μS and the pulse period is 4 μS has a duty cycle of 25 %. The pulse duration is normally calculated for positive pulses unless negative duty cycle is specified.

Period :- A portion of time as limited and determined by some recurring phenomenon as by the completion of a revolution of one of the heavenly bodies.

Pulse width :- An interval between leading and trailing edge medians. The specified and displayed value is that obtained with fastest edges, essentially equal to the interval from the start of the leading edge to the start of the trailing edge. In Pulse waveform the interval between the time during the first transition that the pulse amplitude reaches a specified fraction of its final amplitude and the time pulse amplitude drops on the last transition to the same level.

Signal :- A signal is a real or complex valued function of one or more real variables. Or a signal is an electric current or electromagnetic field used to convey data, gesture, action or sound from one place to another place. The signal is said to be one dimensional.