Difference Between PAM, PWM and PPM

In a communication system, the modulation is an important step. Modulation is the process of transmitting a message signal (Baseband signal with low frequency) from transmitter to receiver without changing its characteristics (like amplitude, frequency, phase) by using a carrier signal (high frequency) which varies in accordance with the instantaneous values of the low frequency wave by keeping its frequency and phase constant.

The modulation techniques are classified into two major types: analog and digital or pulse modulation. We have discussed previously the different types of modulation techniques, let us understand the basic difference between PAM, PWM, and PPM.

Types of Modulation Techniques
Types of Modulation Techniques

Before going to discuss the difference between PAM, PWM, and PPM, let us discuss individually each. All these are pulse analog modulation techniques.

Pulse Amplitude Modulation

By varying the amplitude of the pulses (the carrier signal) in proportion to the instantaneous values of the analog signal (the message signal).

Pulse Amplitude Modulation (PAM) Signals
Pulse Amplitude Modulation (PAM) Signals

The above figure illustrates the time-domain representation of the PAM technique which mentions the analog message and PAM modulated signal as an output.

Pulse amplitude modulation is used in the popular Ethernet communication standard. The PAM modulator and demodulator circuits simple compared to other kinds of modulation and demodulation techniques.

There are two categories of PAM techniques, one is the pulses have the same polarity and the other in which the pulses can have both positive and negative polarities according to the amplitude of the modulating signal.

Pulse Width Modulation

The Pulse width Modulation– By varying the width of the pulses (the carrier signal) in proportion to the instantaneous values of the analog signal (the message signal).

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The width of the pulse varies, but the amplitude of the pulse remains constant. Amplitude limiters are used to make the amplitude constant. These circuits clip-off the amplitude, to a preferred level and hence the noise is limited.

There are three types of PWM. They are

  • The leading edge of the pulse being constant, the trailing edge varies according to the message signal.
  • The trailing edge of the pulse being constant, the leading edge varies according to the message signal.
  • The center of the pulse being constant, the leading edge and the trailing edge varies according to the message signal.

Pulse Position Modulation

By varying the position of the pulses (the carrier signal) in proportion to the instantaneous values of the analog signal (the message signal).

Pulse position modulation is done in accordance with the pulse width modulated signal. Each trailing of the pulse width modulated signal becomes the starting point for pulses in the PPM signal.

Hence, the position of these pulses is proportional to the width of the PWM pulses. But the main disadvantage of the PPM modulation technique is, The synchronization between transmitter and receiver must be needed.

Difference Between PAM, PWM, and PPM
Difference Between PAM, PWM, and PPM

In all the above cases, we detect the message of the pulse modulated signal and reconstruct the original analog signal.

Difference Between PAM, PWM, and PPM

The below table gives a detailed difference between PWM, PAM, and PPM.

Sr. No.ParameterPAMPWMPPM
1Type of CarrierTrain of PulsesTrain of PulsesTrain of Pulses
2Variable Characteristic of the Pulsed CarrierAmplitudeWidthPosition
3Bandwidth RequirementLowHighHigh
4Noise ImmunityLowHighHigh
5Information Contained inAmplitude VariationsWidth VariationsPosition Variations
6Power efficiency (SNR)LowModerateHigh
7Transmitted PowerVaries with an amplitude of pulsesVaries with variation in widthRemains Constant
8Need to transmit synchronizing pulsesNot neededNot neededNecessary
9Bandwidth depends onBandwidth depends on the width of the pulseBandwidth depends on the rise time of the pulseBandwidth depends on the rise time of the pulse
10Transmitter powerInstantaneous transmitter power varies with the amplitude of the pulsesInstantaneous transmitter power varies with the amplitude and width of the pulsesInstantaneous transmitter power remains constant with the width of the pulses
11The complexity of generation and detectionComplexEasyComplex
12Similarity with other Modulation SystemsSimilar to AMSimilar to FMSimilar to PM

This article is all about the difference between PAM, PWM, and PPM techniques. Furthermore, for any help on Electronic projects or doubts regarding this article, you can contact us by commenting in the comment section given below.

One Comment

  1. thanks, this is VERY GOOD comprehensive explanation;

    all the best to you;
    regards
    surv

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