  We apply the Nonequilibrium Green's Function (NEGF) formalism to the problem
of a multi-terminal nanojunction subject to an arbitrary time-dependent bias.
In particular, we show that taking a generic one-particle system Hamiltonian
within the wide band limit approximation (WBLA), it is possible to obtain a
closed analytical expression for the current in each lead. Our formula reduces
to the well-known result of Jauho et. al. [doi:10.1103/PhysRevB.50.5528] in the
limit where the switch-on time is taken to the remote past, and to the result
of Tuovinen et. al. [doi:10.1088/1742-6596/427/1/012014] when the bias is
maintained at a constant value after the switch-on. As we use a partition-free
approach, our formula contains both the long-time current and transient effects
due to the sudden switch-on of the bias. Numerical calculations performed for
the simple case of a single-level quantum dot coupled to two leads are
performed for a sinusoidally-varying bias. At certain frequencies of the
driving bias, we observe `ringing' oscillations of the current, whose
dependence on the dot level, level width, oscillation amplitude and temperature
is also investigated.
