In the field of digital signal processing, quantization refers to the process of approximating a continuous value (or a large number of possible discrete values) of a signal to a limited number (or less) of discrete values. Quantization is mainly used for the conversion from continuous signal to digital signal. A continuous signal is sampled into a discrete signal, and the discrete signal is quantized into a digital signal. Note that discrete signals usually do not need to be quantized, but may not be discrete in the value domain or need to be quantized. The sampling and quantization of signals are usually realized by ADC.