Pulse code modulation - Sampling, quantization and encoding

PULSE CODE MODULATION

Pulse code modulation is a way of transmitting analog data in digital format. Digital signal are binary, it represents only two possible state 1 or 0. In PCM( Pulse code modulation), an analog signal is sampled and converted to a series of binary bits. It includes three steps sampling, quantization and encoding. In pulse code modulation, amplitude of analog wave is sampled at regular intervals and then converted into digital form (binary 0 and 1). 

But if there is a difference between sender side analog signal and receiver side digital signal, then it is called quantization error.

SAMPLING

To sample a continuous signal, a sampler is required. A sampler is a system that extracts samples from a continuous signal. Sampling is a process of measuring the amplitude of a continuous-time signal at discrete instants. It converts a continuous-time signal to a discrete-time signal.

QUANTIZATION

Quantization is a method of representing the sampled values of the amplitude by a finite set of levels. It converts a continuous-amplitude sample to a discrete-amplitude sample. Quantization is used to limit the amplitude of these samples.

The difference between an input value and its quantized value (such as round-off error) is referred to as quantization error. A device that performs quantization is called a quantizer. An analog-to-digital converter is an example of a quantizer.

Quantization level

If there is a 8-bit sample rate then it gives 256 possible levels.

A/D output = n bits per sample (quantization level M=2n)

    8 bits = 256 levels

   16 bits = 65,536 levels

QUANTIZATION DISTORTION

It is a deviation between samples at receiver and sender side.