  In this work, a modified, lumped element graphene field effect device model
is presented. The model is based on the "Top-of-the-barrier" approach which is
usually valid only for ballistic graphene nanotransistors. Proper modifications
are introduced to extend the model's validity so that it accurately describes
both ballistic and diffusive graphene devices. The model is compared to data
already presented in the literature. It is shown that a good agreement is
obtained for both nano-sized and large area graphene based channels. Accurate
prediction of drain current and transconductance for both cases is obtained.
