Write short note on Quantization.

Quantization: This is the first step in PCM. The whole amplitude range of the modulating signal is divided in a number of standard levels termed as quantization levels at equal intervals as demonstrated in figure. These levels are, after that transmitted, in binary code. Therefore, the actual number of these standard levels is a power of two as 4, 8,16,32,64,128 and so on. For the sake of simplicity, figure demonstrates only eight levels, however practical systems use 128 levels or even higher. A new signal is generated through producing, for every sample, a voltage level equivalent to the mid-point level of the standard level wherein the sample falls. Therefore if a range of 0-4 V were divided in four 1V standard levels and the signal was sampled while this was 2.8V, the quantizer will output a voltage of 2.5 V, and hold which level till the next sampling time 2.5 V corresponds to the midpoint of the third standard level. The result in a stepped wave forms that follow, the contour of the modulating signal. This discritisation of the modulating signal is termed as Quantization. Given figure demonstrates the modulating signal m(t) and quantized signal (mq(t)) when eight standard levels are utilized. The quantized wave forms are an approximation to the original signal. The difference in between the two wave forms amounts to noise added to the signal through the quantization process. Therefore the error introduced is termed as quantizaton error.

FIG - Modulating Signal and Quantized Signal