MOSFETs as High-Power DC Controlled Capacitors

Motivation: Varactor diodes find wide application as direct current controlled variable capacitors in low-power RF applications. However, varactors are typically restricted to receive side applications due to low power handling capabilities. Goal(s): This research aims to develop DC controllable capacitors capable of operating at transmit side power level. Approach: Controlling drain-to-source voltage of a MOSFET changes the device drain-to-source capacitance. Modules are constructed as drop-in replacements for mechanically variable capacitors. Results: MOSFETs were successfully used for a broadband matching network and near-zero current decoupling of transmit coils both tested with up to 1000 watts of input power. Impact: MOSFETs as DC-controllable capacitors provide an alternate to varactor diodes that can be employed in the transmit chain, enabling applications such as matching networks and effective near-zero current decoupling.