  Signal digitisation may produce significant effects in balloon - borne or
space CMB experiments, since the limited bandwidth for downlink of data
requires imposes a large quantisation step q applied on board by the instrument
acquisition chain. In this paper we present a study of the impact of the
quantization error in CMB experiments using, as a working case, simulated data
from the Planck/LFI. At TOD level, the effect of the quantization can be
approximated as a source of nearly normally distributed noise. At map level,
the data quantization alters the noise distribution and the expectation of some
higher order moments. Finally, at the levell of power spectra, the quantization
introduces a power excess, that, although related to the instrument and mission
parameters, is weakly dependent on the multipole l at middle and large l and
can be quite accurately subtracted, leaving a residual uncertainty of few % of
the RMS uncertainty. Only for l<30 the quantization removal is less accurate.
