the process of converting analog signals to digital signals is called ?
CONVERSION (convert) OF ANALOG SIGNALS TO DIGITAL SIGNALS
In communication systems, sometimes it happens that we are available with analog signal, however, we have to transmit a digital signal for a particular application. In such cases, we have to convert an analog signal into digital signal. This means that we have to canvert a continuous time signal in the form of digits. To see how a signal can be converted from analog to digital form, let us consider an analog signal as shown in figure 1.6(a). First of all, we get sample of this signal according to sampling theorem. For this purpose. we mark the time-instants t0, t1, t2 and so on, at equal time-intevals along the time axis. At each of these time-instants, the magnitude of the signal is measured and thus samples of the signal are taken. Figure 1.6(b) shows a representation of the signal of figure 1.6(a) in terms of its samples.
Now we can say that the signal in figure 1.6(b) is defined only at the sampling instants. This means that it no longer is a continuous function of time, but rather, it is a discrete-time signal. However, since the magnitude of each smaple can take any value in a continuous range, the signal in figure 1.6 (b) is still an analog signal.
This difficulty is neatly resolved by a process known as quantization. In quantization, the total, amplitude range which the signal may occupy is divided into a number of standard levels.
As shown in figure 1.6(c), amplitudes of the signal x(t) lie in the range
(- mp, mp) which is partitioned into L intervals, each of magnitude Dv=. Now, each smaple is approximated or rounded off to the nearest quantized level as shown in figure. Since each sample is now approximated to one of the L numbers, therefore the information is digitized.
The quantized signal is an approximation of the original one. We can improve the accuracy of the quantized signal to any desired degree simply by increasing the number of levels L.
FIGURE 1.6 (a) An analog signal, (b) Samples of analogsignal, (c) Quantization