Pulse Code Modulation (PCM)

After getting an idea about the sampling & Quantization process we are now ready to describe pulse code modulation (PCM)

PCM is the most basic form of digital pulse modulation.

PCM:- In PCM a message signal is represented by a sequence of coded pulses. which is accomplished by representing the signal in discrete form in both time and amplitude.

PCM Block Diagram:-

The Block Diagram of a PCM system is given in the following figure. This Block Diagram consists of the Basic elements of a PCM system.

i. Transmitter

ii. Transmission path.

iii. Receiver.

PCM Transmitter:-  The basic operations performed in the transmitter are

  • Sampling
  • Quantization
  • Coding

is known as Analog-to-Digital conversion (ADC).

LPF:- The LPF prior to the sampler is inclined to prevent the aliasing of the message signal.

Sampler:- Converts the analog Band limited Signal to a discrete signal.

ADC:- It’s a device that performs two operations known as Quantization and Encoding.

Regenerative repeater:- PCM encoded output is transmitted through the transmission path to the receiver, during transmission the PCM output get distorted in the channel by noise which can be generated by the device called regenerative repeater.

PCM Receiver:- The essential operations in the receiver are regeneration of impaired PCM output decoding.

The device that performs decoding and demodulation at the Receiver is known as (DAC) Digital-to-Analog Converter.

A few points about PCM:-

  1. we know that PAM, PWM &PPM analog pulse modulation techniques. where as PCM is a pure Digital Modulation scheme.
  2. It should be understood that the PCM is not a modulation technique in the conventional sense.
  3. The output of PCM is in the coded digital form that is in the form of code words.  a PCM system consists of PCM encoder as well as Decoder.

Author: Lakshmi Prasanna Ponnala

Completed M.Tech in Digital Electronics and Communication Systems.

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