Design and Analysis of the DC–DC Converter With a Frequency Hopping Technique for EMI Reduction

As more circuit functions are integrated within a single die or small integrated package, the number of electromagnetic interference (EMI) problems caused by dc-dc converters is growing. In this paper, the dominant electromagnetic emission source on the dc-dc converter is identified by analyzing the power spectrum of the nodes. The noise scanner method is applied to a packaged single-chip prototype dc-dc converter. The results show that the dominant source of electromagnetic emission is the switching node of the converter, not the output node. The frequency hopping technique (FHT) is applied to the dc-dc converter to reduce the emission at the switching node, and its effectiveness is analyzed mathematically and experimentally. The mathematical model of FHTs is proposed to analyze its effectiveness in reducing EMI, and the optimal design using the FHT and dead-time control is fabricated with 0.18-μm CMOS technology. The measured power spectrum reduction by using the optimal FHT design and dead-time control at the switching node is 16 dB. The EMI reduction amount of the proposed design measured by the IC-stripline method is 12.6 dB at the fundamental switching frequency.

I. Introduction

As the integration density of electronic devices becomes higher, the number of different cores within a chip or within a package continuously increases. Often, different cores of the design require different power supply voltages; thus, the power management unit needs to be integrated to provide different voltages. The power conversion efficiency is a critical problem particularly in portable devices that consume power from limited sources, such as batteries. Therefore, the dc–dc converter is commonly used in almost all electronic devices due to the high efficiency of dc voltages conversion. The switching dc–dc converter operates based on the charging and discharging activities of the passive components (inductor and capacitor) [1]. These activities require high in-/out-current and high voltage variations within the circuit nodes, which causes problems related to the electromagnetic interference (EMI) of the system [2], [3]. The EMI generated from the dc–dc converter will affect all the adjacent devices [4]. With a good understanding of the EMI in dc–dc converters, the system can be designed to eliminate this EMI problem. Therefore, in this paper, the EMI generating issue of the dc–dc converter is analyzed for optimization.