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3.7 Selection of Sample Frequency 67
Figure 3.3 Aliasing because of under sampling
Generally, the analog
signal must be bandlim-
ited and the sample rate
must be larger than twice
the bandwidth. However, if
the analog signal is band-
pass filtered before the
sampling, then the sam-
pling frequency may be as
low as twice the signal
bandwidth [15, 29]. The
bandlimit restriction need
not be satisfied if the infor-
mation contained in the
digital signal is to be
reduced by subsequent
digital filtering.
Figure 3.4 Aliasing of non-bandlimited signal
3.7 SELECTION OF SAMPLE FREQUENCY
In this section we will discuss
selection of sampling frequency.
To ensure that the analog signal
is bandlimited, it is necessary to
use an anti-aliasing filter before
the sample-and-hold circuit
(S&H) as shown in Figure 3.5. A Figure 3.5 Analog-to-digital conversion
