  The recent detection of the primordial gravitational waves from the BICEP2
observation seems to be in tension with the upper bound on the amplitude of
tensor perturbations from the PLANCK data. We consider a phenomenological model
of inflation in which the microscopical properties of the inflationary fluid
such as the equation of state $w$ or the sound speed $c_s$ jump in a sharp
manner. We show that the amplitude of the scalar perturbations is controlled by
a non-trivial combination of $w$ and $c_s$ before and after the phase
transition while the tensor perturbations remains nearly intact. With an
appropriate choice of the fluid parameters $w$ and $c_s$ one can suppress the
scalar perturbation power spectrum on large scales to accommodate a large
tensor amplitude with $r=0.2$ as observed by BICEP2 observation.
