Biomedical Engineering Reference
In-Depth Information
Sampled signal continuous in amplitude but discrete in time
1.0
0.8
0.6
0.4
0.2
0.0
0
10
20
30
40
50
60
70
80
90
100
-0.2
-0.4
-0.6
-0.8
-1.0
Time (some unit)
FIGURE 6.3
:
An analog signal that has been sampled such that the sampled signal is “continuous
in amplitude but defined only at discrete points in time.” The dashed line is the original sinusoidal
signal
finite set of discrete values at each of these points. A digital signal can represent samples
of an analog signal at discrete points in time.
There are two distinct operations in converting from analog to digital signals:
1.
Sampling
, which is the transition from continuous-time to discrete-time
2.
Sample quantization
, the transition from a continuous changing amplitude to a
discrete amplitude representation
Reversing the process from digital to analog involves a similar two-step procedure in
reverse.
6.2 SAMPLING THEORY
Before getting into the topic on analog-to-digital conversion, it is necessary to have
some knowledge and understanding of the theory behind the sampling of data. The
mechanism for obtaining a sample from an analog signal can be modeled in two ways.
Ideally, an instantaneous value of the signal is obtained at the sample time. This model
Search WWH ::
Custom Search