Analytical voltage dependence of an unsaturated MESFET´s gate capacitance

Using a one-dimensional gradual channel analysis, the authors derive an analytical expression for the gate-source capacitance of an unsaturated MESFET as a function of the applied drain and gate voltages. Experimental measurements of the dependence of the gate-source capacitance on drain voltage show good agreement with theory when the device is biased below saturation. As the MESFET is biased into saturation the measured capacitance decreases with increasing drain voltage at a slightly faster rate than that predicted by the gradual channel theory due to high-field effects. These results show that the derived analytical expression may be useful for the analysis of the characteristics of MESFET´s that are biased in the linear region.<>