Pulse Amplitude Modulation

Objective
To perform and understand the characteristics of pulse amplitude modulation.

Introduction

Just as the amplitude, frequency, or phase of a sinusoidal carrier can be modulated with an information signal, so as the amplitude, frequency or phase or position of pulses in a pulse modulation system can also be modulated. This is a variant of pulse amplitude modulation, in which the pulses amplitudes are transmitted in binary code.

Pulse Code Modulation
PCM is the method of converting an analog signal in to a digital signal (A/D) conversion. An analog signal is characterized by the fact that its amplitude can take on any value over a continuous range. This means that it can take on an infinite number of values. On the other hand, digital signal amplitude can take on only a finite number of values. An analog signal can be converted into a digital signal by means of sampling and quantizing.

Sampling: - In signal processing, sampling is the reduction of a continuous signal to a discrete signal. Sampling can be done for functions varying in space, time or any other dimensions and similar results are obtained in the two or more dimensions.
The sampling frequency or sampling rate Fs is defined as the number of samples obtained in one second (samples per second).

Fs = 1 / Fs


Quantization: - Quantization is the process of rounding off the values of the flat-top samples to certain predetermined levels in order to make a finite and manageable number of levels available to the A/D converter.
In the quantization process, the total signal range is divided into a number of subranges. Each sub range has its mid-value designated as the standard or code level for that range. Comparators are used to determine which subranges a given pulse amplitude is in, and the code for that subrange is generated.