Agilent Technologies 93000 SOC Series Training Manual page 556

Appendix A
By means of oversampling, an 18-bit resolution can be achieved
even with a 16-bit digitizer.
Oversampling Method
Coherent Sampling
We have already mentioned that digital signal processing requires
some kind of synchronization between the signal frequency and
the sampling frequency in order to obtain accurate and
reproducible results.
The ideal sampling method is one that allows us to select a
minimal, but sufficient number of samples N, and then distribute
the samples over the test period in a way that is informationally
equivalent to uniform distribution over one signal cycle.
N sampled data points must contain M whole signal cycles.
The systematic method to achieve this synchronization between N
and M is called coherent sampling.
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