Modeling and Analysis of Large-Signal RFI Effects in MOS Transistors

The ability of radio-frequency (RF) interference signals to upset or disrupt electronic equipment is a matter of concern, and identification of the physical mechanisms leading to device malfunction is of prime importance. This paper presents experimental and theoretical results and analyzes the effects of a large-signal microwave excitation up to 2 GHz on several commercial small-signal MOS transistors. For frequencies beyond the maximum operating frequency, experimental results show RF signal rectification in the devices, and these results are confirmed by SPICE simulations using extracted models for the transistors, including package and test circuit parasitics, with excellent agreement with experiments. Analysis of internal transistors currents and voltages finally leads to the conclusion that the observed rectification effect is not due to active nonlinearities of the devices, but rather due to the nonlinear overlap and parasitic drain-bulk diode capacitances of the MOS transistors. In particular, the role of the nonlinear voltage dependence of the junction capacitance is highlighted. Finally, a simplified model is proposed to reproduce this behavior.