Electromagnetic interference (EMI) issues for mixed-signal system-on-package (SOP)

Electromagnetic interference (EMI) issues in implementing a mixed-signal system-on-package (SOP) are investigated. Each of the testbeds utilized in our experimentations consists of a digital circuit and a RF front-end circuit with embedded passives, but they vary in terms of the route of the digital trace. With these testbeds, we demonstrate two different EMI mechanisms. The first results in EMI due to capacitive coupling through a small slot and intermodulation between the digital and RF signals. Even when the frequency of the digital signal is much lower than that of the RF signal, this mechanism causes new harmonics of the digital signal to appear around the frequency of the RF signal. The second mechanism produces EMI due to coupling through the common power bus in the package. To prevent such EMI issues, we describe differential signaling of the digital interface as our future work. Our results indicate the correct direction for EMI design in developing mixed-signal SOP.