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For a digitally sampled system, some useful definitions of bandwidth are:
SIGNAL BANDWIDTH -- analog bandwidth of a region of interest
ANALYSIS BANDWIDTH -- half the sample rate
PERCENTAGE BANDWIDTH -- fraction of the region of interest (SIGNAL BANDWIDTH) occupied by a particular signal of interest
Typically, the ANALYSIS BANDWIDTH is chosen to be 1-1/2 times the SIGNAL BANDWIDTH to avoid undesired aliasing (folding) of the skirts of the SIGNAL BANDWIDTH. Notice that the term SIGNAL BANDWIDTH is somewhat ambiguous, since it can refer either to the bandwidth of a signal within a region or to the region itself. Because the region is defined by a pre-sampling filter, this bandwidth is usually referred to as the SIGNAL BANDWIDTH independently of the type of signal which might appear in that region. The significance of PERCENTAGE BANDWIDTH relates to integration gain. If the percentage bandwidth is small (typically a highly coherent CW signal), then integration gain is possible. If the percentage bandwidth is large (typically a pulsed signal), then integration gain is not possible. See Dynamic Range.
For analog or digital systems, the following definitions are also useful:
LARGE-SIGNAL BANDWIDTH -- The usable bandwidth of a device when the output signal undergoes full-scale (rail-to-rail) variations.
SMALL-SIGNAL BANDWIDTH -- The usable bandwidth of a device when the output signal undergoes variations which are only a small percentage of full-scale variations.
Typically, due to slew-rate considerations for physical devices, the SMALL-SIGNAL BANDWIDTH is much greater than the LARGE-SIGNAL BANDWIDTH. See Slew Rate.