Résumé en anglais

Let X̄Δ be the process obtained by linear interpolation from discrete observations of a diffusion X. In the first part of this paper we study the statistical properties of the observation sgn X̄Δ. In the second part we prove that the number of zero-crossings of X̄Δ, suitably normalized, converges in (L2-norm) to the zero local time of X.