  The analytical model of the small-signal current and capacitance
characteristics of RF graphene FET is presented. The model is based on explicit
distributions of chemical potential in graphene channels (including ambipolar
conductivity at high source-drain bias) obtained in the framework of
drift-diffusion current continuity equation solution. Small-signal
transconductance and output conductance characteristics are modeled taking into
account the two modes of drain current saturation including drift velocity
saturation or electrostatic pinch-off. Analytical closed expression for the
complex current gain and the cutoff frequency of high-frequency GFETs are
obtained. The model allows describe an impact of parasitic resistances,
capacitances, interface traps on extrinsic current gain and cut-off frequency.
