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 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 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). 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 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. Parameter PAM PWM PPM 1 Type of Carrier Train of Pulses Train of Pulses Train of Pulses 2 Variable Characteristic of the Pulsed Carrier Amplitude Width Position 3 Bandwidth Requirement Low High High 4 Noise Immunity Low High High 5 Information Contained in Amplitude Variations Width Variations Position Variations 6 Power efficiency (SNR) Low Moderate High 7 Transmitted Power Varies with an amplitude of pulses Varies with variation in width Remains Constant 8 Need to transmit synchronizing pulses Not needed Not needed Necessary 9 Bandwidth depends on Bandwidth depends on the width of the pulse Bandwidth depends on the rise time of the pulse Bandwidth depends on the rise time of the pulse 10 Transmitter power Instantaneous transmitter power varies with the amplitude of the pulses Instantaneous transmitter power varies with the amplitude and width of the pulses Instantaneous transmitter power remains constant with the width of the pulses 11 The complexity of generation and detection Complex Easy Complex 12 Similarity with other Modulation Systems Similar to AM Similar to FM Similar to PM This article is all about the difference between PAM, PWM, and PPM techniques. 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