EMI/EMC Characterization of Mixed Radio Frequency-Digital Circuits

John L. Volakis 

ElectroScience Lab., Electrical and Computer Engineering Dept.,

The Ohio State University,

1320 Kinnear Road, Columbus, OH, 43212, USA

            Due to the ever increasing clock frequencies and radio (RF) interference (unintentional or intentional) onto electronic and computer systems, issues relating to electromagnetic compatibility and interference (EMI/EMC) are of contemporary importance.  Of particular interest is certainly the effect of EMI/EMC onto digital logic circuits. To do so, it is important to evaluate ambient signal penetration into structural enclosures and subsequently onto cables as well as RF integrated circuits that may be part of the printed circuit boards (PCBs) used for logic circuits.

            In this presentation, we summarize recent frequency domain analysis methods for EMI/EMC characterization of entire systems. Specific methods, best suited for the analysis of structures, cables, printed RF circuits and devices (amplifiers, mixers, etc.) and digital circuits are presented and hybridized for system level analysis.  We will present theoretical tools and validation of these for concurrent on-board and off-board EMI analysis of mixed RF-Digital Circuits.  After a brief discussion of cable and structure characterization via generalizations and hybridizations of transmission line methods, we focus on a new port analysis technique based on the S-Parameter matrix for on-Board EMI/EMC analysis. Specifically, we introduce a novel hybrid S-Parameter characterization to account for external field coupling to RF-digital circuit boards. This (frequency domain) approach may circumvent CPU bottlenecks associated with time domain methods. The novelty of the introduced hybrid S-parameter matrix is the introduction of additional port(s) to handle the external plane wave excitation. As such, a single matrix is developed to handle both on-board and off-board EMI problems, simultaneously. The new hybrid S-Parameter matrix approach can be easily integrated into circuit solvers such as HSPICE and Advanced Design System (ADS, Agilent Technologies). It also allows for both time domain and Harmonic Balance simulations of non-linear RF-digital components via broad-band network characterization.

            For experimental validation, analysis and measurements will be presented of example fundamental circuit blocks such as RF Power Amplifiers (PAs), inverters and other basic components of sensor systems such as timers. At the system level, we consider the performance of a 3G wireless communication system subject to EMI and obtain the Bit Error Ratio (BER). Specifically, a W-CDMA signal is tracked prior to and after the application of EMI/EMC and channel noise. In this context, the nonlinearity of a RF Power Amplifier is exploited by introducing additional EMI noise at the input to trigger spectral regrowth and, thus, cause interference at adjacent channels. This work is also applicable to automobile sensor interference exposed to High Power Short Pulse Microwaves with varying repetition rate and pulse widths.