An apparatus for determining and/or monitoring at least one process variable of a medium. The apparatus includes: at least one mechanically oscillatable unit; a driving/receiving unit, which, starting with an electric, excitation signal, excites the mechanically oscillatable unit to execute mechanical oscillations, and which receives the mechanical oscillations of the mechanically oscillatable unit and converts them into an electric, received signal; and an electronics unit, which, starting with the electric, received signal, generates the electric, excitation signal and sends it to the driving/receiving unit. The electronics unit is embodied in such a way that it generates the excitation signal, such that a predeterminable phase difference exists between the excitation signal and the received signal. Present in the electronics unit is at least one all-pass filter for tuning the phase difference.