Q. Write short note on Quantization?

Quantization: This is first step in PCM. Total amplitude range of the modulating signal is divided into a number of standard levels called quantization levels at equal intervals as demonstrated in figure. These levels are then transmitted in binary code. Thus actual number of these standard levels is a power of two like 4, 8,16,32,64,128 etc. For the sake of simplicity, Figure displays only eight levels, though practical systems use 128 levels or even higher. A new signal is generated by producing, for every sample, a voltage level corresponding to mid-point level of the standard level in which sample falls. So if a range of 0-4 V were divided into four 1V standard levels and signal was sampled when it was 2.8V, quantizer will output a voltage of 2.5 V and hold that level till next sampling time 2.5 V corresponds to midpoint of the third standard level. This leads to a stepped wave form which follows contour of the modulating signal. This discretisation of modulating signal is termed as Quantization. Figurebelow demonstrates modulating signal m (t) and quantized signal (mq (t)) when eight standard levels are used. Quantized wave forms are an approximation to the original signal. Difference between two wave forms amounts to noise added to the signal by quantization process. Error introduced so is called quantization error.