Explain what is meant by quantization noise and comment on Adaptive delta modulation.

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written 6.7 years ago by

teamques10 ★ 68k

Quantization is a process of approximating or rounding off. The sampled signal in PCM transmitted is applied to the quantizer block
Quantizer converts the sampled signal into an approximate quantized signal which consists of only finite number of predicted voltage levels
Each sampled value at the input of the quantizer is approximated or rounded off to the nearest standard predicted voltage level. These standard levels are called as quantization levels
The quantized signal xq (t) is the approximation of x(t). The difference between them is called as quantization error or as quantization noise. This error should be small as possible
To minimize the quantization error, we need to reduce the step size ‘s’ by increasing the number of quantization levels Q.
If we do not use the quantizer block in the PCM transmitter, then we will have to convert each and every sampled value into a unique digital word.
This will need a large number of bits per word (N). This will increase the bit rate and hence the bandwidth requirement of the channel.
The difference between the instantaneous values of the quantized signals and the input signal is called as quantization error or as quantization noise.
The mean square value of the quantization error= s^2/12

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Adaptive Delta Modulation

To overcome the quantization errors due to slope overload and granular noise, the step size (δ) is made adaptive to variations in the input signal x(t).
Particularly in the steep segment of the signal (t) , the step size is increased .When the input is varying slowly , the step size is reduced .Then the method is called Adaptive Delta odulation(ADM).
The adaptive delta modulators can take continuous changes in step size or discrete changes in step size.

Advantages of ADM

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