RFI Noise Source Quantification Based on Reciprocity

In modern mobile electronic systems, several high speed digital ICs often working simultaneously and can cause interference issues with nearby antennas at the same time. In this paper, a method to quantify the contribution of multiple noise sources radiating simultaneously is proposed. The reciprocity theorem based radio frequency interference (RFI) estimation can be decomposed into forward and reverse problems. Multiple imaginary Huygens' boxes are introduced to enclose different IC noise sources. In forward problem, the ICs are working and the tangential E and H fields on corresponding Huygens' boxes can be obtained. In reverse problem, the victim antenna is excited while the noise sources are turned off. On the same set of Huygens' boxes, the tangential electromagnetic fields from the radiating antenna can also be recorded. With tangential E and H fields in both the forward and reverse problems on different Huygens' boxes, the coupled voltage contributed by multiple noise sources can be calculated separately using reciprocity theorem. The RFI noise source quantification method is validated by simulation. A test structure with two simultaneously radiated traces and a planar inverted-F antenna (PIFA) is used.

1. Introduction

In modern mobile electronic device design, high speed digital circuits can often cause radio frequency interference to the RF modules, degrading their performance. With the increasing speed of digital circuits, the electromagnetic interference between them becomes more and more critical. Meanwhile, as the device sizes are preferred to be smaller, the internal structures inside these devices are more and more complex. Many digital electronic parts can serve as potential noise sources for RF receivers. In addition, multiple noise sources can radiate simultaneously, such as the USB port and the internal SSD [1]. This will further increase the complexity to identify the coupling mechanisms and the real trouble makers. To consider the RFI issues during a particular circuit design, it is important to quantify the contribution of each part and evaluate the total coupled noise voltage prior to the final circuit layout.