| The purpose of the research described herein was to develop large-signal models for semiconductor RF power devices. The lumped-charge modeling approach, developed with low-frequency power switching devices in mind, was seen as having good potential for RF devices also. RF power MOSFETs were of particular interest because of their highly nonlinear capacitance behavior, their particular advantages for RF application and their rapidly increasing application to RF power designs. Such models were nonexistent at the time of this research and according to a major vendor, were greatly needed by both device and circuit designers. A software implementation of a lumped charge model for power MOSFETs, written in the MAST modeling language for the Saber simulator, was available for this purpose. This research describes the determination of the lumped-charge modeling parameters for a Motorola MRF255 RF power MOSFET and the results of simulations of a Motorola test circuit for that device. The simulation results compare very favorably to the manufacturer's published test results. The lumped-charge modeling approach should also be applicable to other large signal RF power devices, such as BJTs, lateral MOSFETs and MESFETs. Lumped charge models for the low-frequency counterparts of such devices have either already been developed or are being considered. |
