Pulse Width Modulation (PWM) - Basic Concepts, Waveform and Definition of PWM Explained

What is Pulse Modulation

Pulse modulation is a type of modulation where some parameter of the pulsed carrier wave is varied as per the instantaneous value of the modulating signal (message signal).

Types of Pulse Modulation Techniques

Pulse modulation can be categorized into 3 types-
1.Pulse Amplitude Modulation (PAM)
2.Pulse Width Modulation (PWM)
3.Pulse Position Modulation (PPM)

Out of these three types of pulse modulation techniques, PWM and PPM come under Pulse Time Modulation (PTM).

Pulse Width Modulation Video [HD]

 

Pulse Time Modulation (PTM)

In pulse time modulation, the timing of pulses of the pulsed carrier is varied. So the variations occur on the time axis. Since it is of two types, Pulse Width Modulation and Pulse Position Modulation, where width and position of the pulses is varied respectively. These changes in width or position take place on the time axis. Therefore PWM and PPM are types of pulse time modulation.

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Now we will understand the Pulse Width Modulation (PWM), in detail-

Pulse Width Modulation (PWM)

Definition:-

In Pulse width modulation, width (duration) of the pulses of the carrier wave is varied according to the modulating signal (message signal).

Let's analyze the waveform of pulse width modulation.
Look at the image given below to see the waveform of pulse width modulated signal. (Click the image to enlarge)-

Pulse Width Modulation Waveform (PWM)

Here you can see waveforms of modulating signal, pulsed carrier wave and pulse width modulated wave.

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As per the definition of pulse width modulation, we know that, in Pulse width modulation, the width of the pulses of carrier wave is varied according to the message signal. So you can see here in the image that as the amplitude of the message signal changes, the width of pulses of the pulsed carrier wave changes accordingly.
You can easily observe here, the width of the pulse is maximum when amplitude of the message signal is at maximum and in the same way, width is minimum when amplitude of the modulating signal is minimum.

Important Observations about Pulse Width Modulation (PWM)

1.Since it is pulse width modulation (pulse duration modulation), therefore only the width (duration) of the pulses of the carrier wave changes. No change takes place in amplitude or position of the pulses.

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2.As the width of pulses changes according to the modulating signal; information is present only in the width of the pulses. In Pulse width modulation, amplitude or position of the pulses contain no information.

Properties of Pulse Width Modulation (PWM) 

1.Power in PWM

In PWM, instantaneous power of the transmitter varies due to variations in width of the pulses.

2.Noise in PWM 

Pulse Width Modulation is less affected by noise due to its constant amplitude. It is also easier to remove noise from the signal as compared to Pulse amplitude modulation.

3.Similarity of PWM with Continuous Wave Modulation

The pulse width modulation is very similar to Frequency Modulation (FM). Since in frequency modulation, frequency of the carrier wave varies according to instantaneous value the of the modulating signal. 
f=1/T 
i.e. frequency is inversely proportional to the time period.
Similarity in PWM, the duration (time period/time duration) varies.

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Need and benefits of modulation
Pulse modulation techniques (PAM, PWM, PPM, PCM)
Comparison of PAM, PWM, PPM modulation techniques
Pulse amplitude modulation (PAM)
Pulse width modulation (PWM)
Pulse position modulation (PPM) 
Pulse code modulation (PCM) advantages and disadvantages
Pulse code modulation (PCM) vs differential pulse code modulation (DPCM)
Sampling theorem and reconstruction (sampling and quantization)