Conductance of MOS transistors in saturation

The finite output conductance of MOS transistors operating in the saturation region is generally attributed to the spreading of the depletion region near the drain which results in a reduction of the channel length. Previous treatments have attempted to calculate the extent of this spreading by describing the electric field distribution using step p-n junction theory. It is shown in this work that the experimentally observed output conductance can be in gross disagreement with such calculations. This discrepancy is due to the fact that, owing to the presence of the gate electrode, the electric field in the drain depletion region is greatly increased.