  Pulsed parametric downconversion (PDC) processes generate photon pairs with a
rich spectral-temporal structure, which offer an attractive potential for
quantum information and communication applications. In this paper, we
investigate the four-dimensional chronocyclic Wigner function of the PDC state,
which naturally lends itself to the pulsed characteristics of these states.
From this function we derive the conditioned time-bandwidth product of one of
the pair photons, a quantity which is not only a valid measure of entanglement
between the PDC photons but also allows to highlight a remarkable link between
the discrete and continuous variable descriptions of PDC. We numerically
analyze PDC processes with different conditions to demonstrate the versatility
of our approach, which is applicable to a large number of current PDC sources.
