Any continuous-time analogue signal can be converted into a digital signal by making discrete both the time and the amplitude axes. The process of making the time axis discrete is called *sampling* and consists of substituting the whole continuous-time analogue signal with a series of its analogue values (samples) taken at particular instants. This process is reversible only if the original signal has limited bandwidth. A well-known result, the fundamental *Sampling Theorem* [2.1]–[2.3], commonly attributed to Shannon orNyquist^{1}, assures that the series of (analogue) samples taken with sampling frequency *f*_{s} is perfectly equivalent to the original signal if

where *B* (bandwidth) is the maximum Fourier frequency in the signal spectrum.

The process of making the amplitude axis discrete is called *quantization.* It consists of dividing the amplitude axis in contiguous intervals and in associating to all the amplitudes within any interval a single amplitude value chosen among them. In practical applications, the number of intervals is finite and the quantized amplitude values can be thus expressed in a numerical form, with a fixed number of digits depending on the total number of intervals chosen.

Through the joint processes of sampling and quantization, therefore, any continuous-time analogue signal is converted to a sequence of numbers or binary ...

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