We present here a new unified analytic model for ballistic and quasi-ballistic transport. Starting from the classical approach of Natori, we enhanced it by taking into account degeneracy and adding consistently an original modelling of Short Channel Effect (SCE) and Drain Induced Barrier Lowering (DIBL) by including quantum confinement. Our model has been validated by comparisons with TCAD simulations and results from literature. Finally, we applied our model to simple circuit elements to evaluate potential performance of a Double-Gate architecture in a Verilog-A environment.