IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. 54, NO. 5, OCTOBER 2012 1137 Chip-Level Design Constraints to Comply With Conducted Electromagnetic Emission Specifications Francesco Musolino, Member, IEEE, Yamarita Villavicencio, and Franco Fiori, Member, IEEE Abstract—This paper deals with the reduction of the conducted electromagnetic emissions of microcontrollers caused by the core block switching. The relationship between the conducted emission at the printed circuit board level and the sources of switching noise at the chip level is evaluated through the analysis of an equivalent circuit that comprises an electric model of the internal building blocks of a microcontroller, the model of its package, and that of the board. The model of the integrated circuit is derived on the basis of functional specifications and technology parameters so that it can be extracted before chip manufacturing. By using this model, and knowing the electromagnetic emission limits to be met, the upper bound of the power supply current spectra of the core logic blocks is evaluated and the effectiveness of common spectrum shaping techniques, like the clock-skewing method or the spread-spectrum clock modulation, is discussed. Index Terms—Circuit modeling, clock-skewing, microcon- trollers, spread spectrum. I. INTRODUCTION T HE contribution to the radiated and conducted emissions of electronic equipment that derives from the switching of modern integrated circuits (ICs) has grown continuously due to the ever-increasing current that the logic gates within an IC draw from the power supply. Such currents flow through the power supply network integrated on silicon and the package frame, thus leading the electromagnetic emission (EME) to be conducted off the chip by means of the unwanted antennas represented by the component pins, the printed circuit board (PCB) traces, and power planes. The IC characterization in terms of EME can help to reduce the system level emissions, and several measurement techniques to estimate IC emissions have been standardized for this purpose by the International Electrotechnical Commission (IEC) [1]. Among the proposed techniques, the 1-Ω method, the 150-Ω method, and the magnetic probe method all make it possible to evaluate the IC conducted EMEs by measuring the spectra of off-chip currents (e.g., I M in Fig. 1) [2], [3]. Besides the description of the test setups and the experi- mental procedures, these standards also define bounds of the off-chip current spectrum (emission masks) with the aim to pro- vide semiconductor manufacturers and users with a method of Manuscript received September 13, 2011; revised January 26, 2012; accepted April 2, 2012. Date of publication May 15, 2012; date of current version October 17, 2012. The authors are with the Department of Electronics and Telecommunica- tions, Politecnico di Torino, 10129 Torino, Italy (e-mail: francesco.musolino@ polito.it; yamarita.villavicencio@polito.it; franco.fiori@polito.it). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TEMC.2012.2195665 Fig. 1. Block diagram of a generic microcontroller. classifying the IC emissions of different devices (see parts 4 and 6 of [1]). Such masks can also be considered as specifications for the conducted emissions of a semiconductor device when tested in accordance with the standard procedure. In order to avoid high costs and time-to-market delay that can result from the redesign of an IC whose conducted emissions do not com- ply with these reference levels, electromagnetic compatibility (EMC)-aware design methodologies must be addressed at the chip level. Some design guidelines can be adopted for this pur- pose, even though the many coupling paths inside a complex IC make the emission of the final device almost unpredictable [4]. Along with these design guidelines, some clock distribution so- lutions, like the spread-spectrum clock (SSC) modulation and the clock-skewing, can also be implemented to shape the spec- tral content of the EMEs [5]. In any case, particular advantages could arise if the transfer function between the off-chip cur- rent I M and the chip-level emission source, i.e., the on-chip switching current I C in Fig. 1, was known before the chip is manufactured. In this paper, a methodology to infer the correlation between the chip-level EME source and the conducted emission at the board level is described. Such a methodology exploits a re- cently developed technique that allows us to find out the equiv- alent circuit of an IC in the early design phases before chip manufacturing, on the basis of the functional and the physical specifications [6]. This methodology has been used in this paper to derive a set of masks for the maximum on-chip supply cur- rent spectrum of an 8-bit microcontroller (μC) that grants the compliance of the IC with the IEC standard levels. Although the method can be generalized, these masks have been computed in 0018-9375/$31.00 © 2012 IEEE