Degradation of the Conducted Radio Frequency Immunity of Microcontrollers Due to Electromagnetic Resonances in Foot-Point Loops

The response of the microcontrollers to conducted radio frequency interference depends strongly on the frequency of the interference signals. As a symbol of the strong frequency dependence, dips appear on the immunity-frequency curve of the microcontrollers. This paper discovers that some of the immunity dips are due to resonances in the current loops through the input and output pins of the oscillator amplifier. Those dips are called foot-point immunity dips. With theoretical analysis, measurements, simulations, and optimizations, this paper gives a systematic description and treatment on the foot-point immunity dips.