PULSE CODE MODULATION:
Modulation is the process of varying one or more parameters of a carrier signal in
accordance with the instantaneous values of the message signal.
The message signal is the signal which is being transmitted for communication and the
carrier signal is a high frequency signal which has no data, but is used for long
distance transmission.
There are many modulation techniques, which are classified according to the type of
modulation employed. Of them all, the digital modulation technique used is Pulse
Code Modulation PCM.
A signal is pulse code modulated to convert its analog information into a binary
sequence, i.e., 1s and 0s. The output of a PCM will resemble a binary sequence. The
following figure shows an example of PCM output with respect to instantaneous values
of a given sine wave.
Instead of a pulse train, PCM produces a series of numbers or digits, and hence this
process is called as digital. Each one of these digits, though in binary code, represent
the approximate amplitude of the signal sample at that instant.
In Pulse Code Modulation, the message signal is represented by a sequence of coded
pulses. This message signal is achieved by representing the signal in discrete form in
both time and amplitude.
BASIC ELEMENTS OF PCM:
The transmitter section of a Pulse Code Modulator circuit consists of Sampling,
Quantizing and Encoding, which are performed in the analog-to-digital converter
section. The low pass filter prior to sampling prevents aliasing of the message signal.
The basic operations in the receiver section are regeneration of impaired signals,
decoding, and reconstruction of the quantized pulse train. Following is the block
