  In this work we discuss observational aspects of three time-dependent
parameterisations of the dark energy equation of state $w(z)$. In order to
determine the dynamics associated with these models, we calculate their
background evolution and perturbations in a scalar field representation. After
performing a complete treatment of linear perturbations, we also show that the
non-linear contribution of the selected $w(z)$ parameterisations to the matter
power spectra is almost the same for all scales, with no significant difference
from the predictions of the standard $\Lambda$CDM model.
