To describe Pulse Code Modulation (PCM) the idea about Sampling and Quantization are required in hand.
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.
- Transmission path.
the basic operations performed in the transmitter are Sampling, Quantization and Coding -Analog to Digital Conversion(ADC).
LPF:- The Low Pass Filter to sampler is inclined to prevent aliasing of the message signal.
Sampler:- Converts the analog band limited signal to discrete signal.
ADC:- It’s a device which performs two operations known as Quantization and Encoding.
Regenerative repeaters:- 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 regenerated by the device called regenerative repeater.
The essential operations in the receiver are decoding, regeneration of impaired PCM output .
the device which performs decoding and demodulation at the receiver is known as (DAC) Digital-to-Analog Converter.
Few points about PCM:-
- we know that PAM, PWM and PPM are analog pulse modulation techniques, where as PCM is a pure Digital Modulation scheme.
- It should be understood that the PCM is not a modulation technique in the conventional sense.
- 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.