Pulse Modulation System- PAM, PWM, PPM.pptx

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1. CHAPTER 2: Part 2 Types of Pulse Modulation System PAM, PWM and PPM By Dr. Sandeep Kumar Singh ECED, MNNIT Allahabad Ref: Simon Haykin , “Chapter 7 THE TRANSITION FROM ANALOG TO DIGITAL “   Communication systems . John Wiley & Sons, 2008.

2. Pulse modulation systems are techniques used in telecommunications to encode analog signals into digital pulses. Pulse Amplitude Modulation (PAM): In PAM, the amplitude of a series of pulses is varied according to the instantaneous amplitude of the analog signal being transmitted. The width and position of the pulses remain constant. PAM is relatively simple but sensitive to noise and distortion . Pulse Width Modulation (PWM): PWM works by varying the width of the pulses in proportion to the instantaneous amplitude of the analog signal. The amplitude and position of the pulses remain constant. PWM is widely used in applications like motor control, audio amplification, and power regulation due to its efficiency and simplicity . Pulse Position Modulation (PPM): In PPM, the position of the pulses within a fixed time frame is varied according to the instantaneous amplitude of the analog signal. The amplitude and width of the pulses remain constant. PPM is less susceptible to noise compared to PAM, but it requires more bandwidth

3. PULSE-AMPLITUDE MODULATION the amplitudes of regularly spaced pulses are varied in proportion to the corresponding sample values of a continuous message signal There are two operations involved in the generation of the PAM signal: 1. ( sample ) Instantaneous sampling of m(t ) every T s seconds , sampling rate f s = 1/ T s 2. (hold) Lengthening the duration of each sample so obtained to some constant value T. This process is called sample and hold

4. PAM signal h(t ) is a standard rectangular pulse of unit amplitude and duration T

5. instantaneously sampled version of m(t ) convolving m  ( t ) with the pulse h(t) Using the sifting property of the delta function

6. PAM signal s(t) is mathematically equivalent to the convolution of m{t), the instantaneously sampled version of m(t ), and the pulse h(t ), FT Also, as discussed previously We have

7. We may use the increased bandwidth consumed by pulses to obtain an improvement in noise performance by representing the sample values of the message signal by some property of the pulse other than amplitude PWM: Samples of the message signal are used to vary the duration of the individual pulses The modulating signal may vary the time of occurrence of the leading edge, the trailing edge, or both edges of the pulse PPM: the position of a pulse relative to its unmodulated time of occurrence is varied in accordance with the message signal

8. PPM signal k p is the sensitivity of the pulse-position modulator s(t ) must be strictly nonoverlapping