Keysight Technologies 3458A Guide D'utilisation page 497

Figure E-12
The rms error (actual) is the error measured relative to the best-fit perfect sine
wave. The rms error (ideal) is the theoretical error from a perfect N bit ADC. For
low resolution instruments, the effective bits is a true measure quality; for high
resolution instruments, the noise associated with any measurement swamps the
actual performance of the ADC. If, however, a large number of samples is taken
or, equivalently, the samples are averaged, the noise can be reduced to the point
where actual quantization and non-linearity errors are evident in the Fourier
transform of the sampled data. This effect is shown in
harmonic of the input signal is actually an integral non-linearity. Averaging ten
samples does not remove its level, whereas the noise floor drops 10 dB.
Keysight 3458A User's Guide
High Resolution Digitizing With the 3458A
With static DC input levels, the analog-to-digital converter may
exhibit an ideal transfer function as shown in 12a. With a
dynamic input, however, errors shown in 12b may appear.
Figure E-13. The third
E
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