Radio Frequency Interference due to Gigahertz On-die Clock and Package/Board-level Mitigation in Mobile Computer Applications

WiFi radio frequency interference (RFI) caused by a 5.76-GHz on-die clock is investigated. It is demonstrated that gigahertz on-die clocks that have no conductive connections to the package and board can introduce significant radio performance degradation to mobile devices. Conventional RFI mitigation approaches focus on megahertz and below GHz. The 5.76-GHz RFI noise mitigation solutions are investigated in package and board levels. The package solution utilizes self-resonance and minimum impedance characteristics of a capacitor in consideration of parasitic components of package. The board solution uses high-frequency ferrite bead that has high resistive and impedance properties at the frequency of the clock noise. The optimum characteristics of the 5.76-GHz filter components proved to provide> 10-dB RFI noise reduction. This work provides good understanding on gigahertz on-die noise propagation and mitigation guideline for designers to develop low-RFI platforms and also may help to debug/reduce such noise.