The analog signal is firstly sampled and then converted into an n-bit binary sequence called code. This code is helpful in transmission. The basic operations that signal undergo are sampling, quantization, and encoding.


ANALOG SIGNAL-->  SAMPLING--> QUANTIZATION--> ENCODING--> DIGITALLY CODED SIGNAL (PCM)

In pulse code modulation, time and amplitude are represented as discrete values.
PCM mainly consists of three steps:
• Sampling
• Quantising
• Encoding
Pulse code modulation is not only a modulation technique, it is also an encoding technique with which the signals are assigned with a definite digital value.
In pulse code modulation each code has an identical number of bits and run-length for transmission.
Basically, it is the only digitally encoded modulation technique for transmission. In the binary system in which the pulse within a prescribed time period represents logic 1 and the lack of pulse within a time period represents logic 0. Which is for specific time intervals.
• If pulse arrives then it is represented as logic 1
• If a pulse does not arrive then it is represented as logic 0

From the above diagram let us see the appliance and its functions

• Bandpass filter
To limit the analog input frequency up to standard voice band ranges from 300Hz to 3000Hz. It is used to band restrict the input signal.
• Sample and hold circuit
It converts the continuous-time analog signal into a discrete-time signal
• Analog to digital
This block converts the discrete-time signal into a digital bitstream
• Parallel to serial converter
Converts n-bit parallel binary sequence into the n-bit binary frame. Serial n-bit digital serial pulse code modulated code
• Transmission path
Physical media like wires, co-axial cables, twisted pairs,s, etc. In the case of the transmission path, regenerative repeaters will be there.
• Regenerative repeaters
These receivers receive, amplify or boost the signals and retransmit them. They are used here to reduce signal attenuation.
• Serial to parallel converters
Converts the received serial PCM code frame into the n-bit parallel stream.

• Digital to analog
Digital to analog conversion is done by successive approximation method. That results in distant time pulses.
• Hold circuit
Reconstruction of the analog signal at the output.
• Low pass filter
A low pass filter helps in transmitting the noise and quantization noise which results in error-free output.

ADVANTAGES OF PULSE CODE MODULATION (PCM)


• PCM is convenient for long-distance communication
• PCM has higher transmitter efficiency than other modulation
• PCM has higher noise immunity than other modulation

DISADVANTAGES OF PULSE CODE MODULATION (PCM)


•The PCM requires more bandwidth while compared to other modulation
• In PCM the following are complex to perform:
(i)encoding
(ii)Decoding
(iii)Quantizing
• PCM is an integrated digital network that can only be realized by a gradual extension of noise.
• PCM is not used in wireless-based communication systems.
• More crosstalk occurs.

APPLICATIONS OF PULSE CODE MODULATION


• The pulse code modulation is most commonly used in the satellite transmission system
• PCM is used in space communication.
• PCM is used in telephony communication.
• The compact disc (CD) is a recent application in the field of pulse code modulation.

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