  We introduce an effective quark-meson-nucleon model for the QCD phase
transitions at finite baryon density. The nucleon and the quark degrees of
freedom are described within a unified framework of a chiral linear sigma
model. The deconfinement transition is modeled through a simple modification of
the distribution functions of nucleons and quarks, where an additional
auxiliary field, the bag field, is introduced. The bag field plays a key role
in converting between the nucleon and the quark degrees of freedom. The model
predicts that the chiral and the deconfinement phase transitions are always
separated. Depending on the model parameters, the chiral transition occurs in
the baryon density range of $(1.5-15.5)n_0$, while the deconfinement transition
occurs above $5 n_0$, where $n_0$ is the saturation density.
