Pulse Code Modulation
Category : JEE Main & Advanced
The pulse amplitude, pulse width and pulse position modulations are not completely digital.
A completely digital modulation is obtained by pulse code modulation (PCM).
An analog signal is pulse code modulated by following three operation.
(1) Sampling : It is the process of generating pulses of zero width and of amplitude equal to the instantaneous amplitude of the analog signal.
The number of samples taken per second is called sampling rate.
(2) Quantisation : The process of dividing the maximum amplitude of the analog voltage signal into a fixed number of levels is called quantisation.
e.g. amplitude 5 V of the analog voltage signal divides into six. Quantisation level viz 0, 1, 2, 3, 4, 5.
Pulses having amplitude between ? 0.5 V to 0.5 V are approximated (quantised) to a value 0 V, amplitude between 0.5 V to 1.5 V are approximated to a value of 1 V and so on.
(3) Coding : The process of digitising the quantised pulses according to some code is called coding.
Coding
| Quantis-ation level | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Binary code | 000 | 001 | 010 | 011 | 100 | 101 | 110 | 111 |
For example consider that voltage amplitude of an analog signal varies between 0 and 7 V. 
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