Relating Dynamics of FET Behavior to Operating Regions

Dispersion effects and the operating regions they effect are identified in a HEMT and a MESFET. Large-signal pulse and small-signal RF measurements reveal a simple structure to the otherwise complicated dynamic behavior of the FETs. A simple model demonstrates how heating, impact ionization, and leakage currents can contribute to this behavior and that each has an effect in specific regions of bias and operating frequency. It is possible to identify operating conditions that will or will not be affected by dispersion with measurements over a wide range of frequencies from dc to microwave and a range of terminal potentials.