Showing papers by "Jun Fan published in 2021"

Inaudible Attack on Smart Speakers With Intentional Electromagnetic Interference

Abstract: This article demonstrates an inaudible attack on smart speakers using electromagnetic interference (EMI). The EMI induces voltages on the order of a few millivolts on conductors, which are then converted into baseband signals by exploiting the inherent nonlinearity of microphones. The EMI signal is specially preprocessed to minimize the useless harmonics generation at the microphone output signals, which significantly improves the recognition rate as well as nullify the previous countermeasures based on the harmonics detection. The sensitive carrier frequency found by our proposed method can improve the attack distance as well. A measurement-based methodology is applied to locate the sensitive regions for noise coupling without knowing the layout of the printed circuit board (PCB), and the transfer function is also obtained to insure the main coupling location. Our experiments show that in open space, intentional EMI under 2.5 W can inject commands at distances up to 2.5 m on smart speakers.

Identifying Interference From Multiple Noise Sources Using Only Magnetic Near Fields

Abstract: As electronic products become increasingly more complicated, multiple noise sources are likely to simultaneously interfere with the radio frequency (RF) receiver. It will be very helpful if the dominant noise source can be identified when solving the RF interference issue in a complex system. This article proposes a method to separately calculate the contributions from multiple noise sources at their overlapped frequencies so that the worse noise source could be identified even when multiple sources radiate simultaneously. The proposed method creatively employs the decomposition method based on the reciprocity theory to calculate the interference contribution from different sources. Furthermore, in the interest of reducing the near-field scanning time and complexity, the magnetic field only scanning method is developed by using the finite-element method (FEM). In the proposed method, Huygens's surface is established for each source. The tangential magnetic near fields on each Huygens's surface were then applied to solve the corresponding tangential electric fields by the FEM. Subsequently, the sources are removed while the corresponding Huygens's surfaces are maintained. The victim structure is excited under these conditions to obtain the tangential magnetic fields on Huygens's surfaces, and a novel FEM procedure is applied to obtain the tangential electric fields. Finally, based on the electric and magnetic fields, the interference from each noise source can be separately estimated based on the reciprocity theory. This method is validated by a numerical example and measurement. This approach can assist engineers in identifying the contribution of coupling from different sources and in efficiently resolving electromagnetic interference issues.

Jitter-Aware Economic PDN Optimization With a Genetic Algorithm

Abstract: This article proposes a jitter-aware decoupling capacitors placement optimization method that uses the genetic algorithm (GA). A novel method for defining the optimization target function in regard to power delivery network (PDN) and power source-induced jitter (PSIJ) optimization based on the GA-based tool is proposed. The proposed method can provide an optimum and economic solution for the number of decoupling capacitors to use in a PDN to reach the target impedance. Then, by modifying the optimization target function with our proposed method, an optimum solution of the number of decoupling capacitors regarding the PSIJ can be obtained. The PSIJ analytical expressions are derived in conjunction with a resonant cavity model that includes the coordinates of the decoupling capacitors and the PSIJ transfer function. The GA-based optimization algorithm with the proposed target function is first applied to optimize the number of decoupling capacitors regarding the PSIJ. Finally, the measured jitters from HSPICE simulation results are used to verify our optimization method such that both the simulated results and analytically calculated results support the efficiency of our proposed optimization method.

A Novel RFI Mitigation Method Using Source Rotation

Abstract: This article proposes a novel radio frequency interference (RFI) mitigation method and applies it to a real consumer electronic device. Through near-field scanning, an equivalent dipole moment of the noise source containing the CPU and DDR memory chip is reconstructed. The near-field components of the victim Wi-Fi antenna are measured to obtain the transfer function. By determining the relationship between the dipole moment and the antenna near field, the noise source is rotated by a certain angle to reduce RFI. Rotating the source to reduce RFI is implemented in such a way that it does not compromise the signal integrity, and it does not require an additional shield can. New boards with the suggested changes are fabricated and the measured results show the RFI reduction up to 8 dB compared with the original board.

Temperature Effects in OTA MIMO Measurement

Abstract: Evaluating transceiver performance in the research and development stage is the basic function of over-the-air (OTA) testing. OTA testing is considered as the standard method for determining the radiated performance of wireless devices. The multiple-input–multiple-output (MIMO) technology used in wireless devices through the integration of multiple antennas is important for the current 4G long-term evolution (LTE) and the future fifth-generation (5G) wireless systems. OTA testing may be the optimal method for MIMO performance evaluation. During MIMO measurement, the transmitting power level of MIMO devices is set to 10 dB lower than the maximum transmitting power level. Because the transmitting power level can affect a device’s physical temperature and, thus, proportionally increase the noise temperature and affect the throughput of the wireless equipment, the MIMO throughput of the device under test (DUT) determined with standard OTA measurement may not reflect real-world usage, and failure to consider the temperature effect of the DUT might contribute to measurement uncertainty. Here, to verify the temperature effect, we modified the radiated two-stage (RTS) procedure for MIMO systems to eliminate this uncertainty and quantify the temperature effect on DUT MIMO throughput. With this proposed method, the measured MIMO performance is a function of the temperature of the DUT, which is determined according to the transmitting power level of the DUT in its thermally stable condition. The proposed method further provides crucial information enabling engineers to optimize functional and EMC designs.

A Pattern-Based Analytical Method for Impedance Calculation of the Power Distribution Network in Mobile Platforms

Abstract: A power distribution network (PDN) is essential in electronic systems to provide reliable power for load devices. With faster load transient current and lower voltage tolerance margin for microprocessors in mobile platforms, it is crucial to optimize the printed circuit board (PCB) design to satisfy the strict target impedance. Conventional modeling methods become impractical in mobile platforms due to the characteristics of high-density interconnect PCB and limited layout space. To overcome these issues, a pattern-based analytical method for the PDN impedance calculation is presented in this article. Based on the localized patterns formulated by the relative relationships between the adjacent vias, parasitic elements are analytically determined for different regions of the entire PCB structure. With the assistance of this method, a practical modeling methodology is developed to construct an equivalent circuit with one-to-one correspondence to the PCB's physical geometry. As a result, the PDN design can be efficiently optimized, especially in the predesign stage, to accelerate the development process. Finally, the proposed method is validated by measurements and full-wave simulations using a real mobile phone PCB in production.

Multiport PDN Optimization With the Newton–Hessian Minimization Method

Abstract: This article proposes an optimization algorithm using the Hessian minimization method, based on the Newton iteration, to evaluate the effectiveness of the placement of multiple decoupling capacitors on a power/ground plane pair. The exact effective decoupling regions are obtained using the Newton iteration method for each decoupling capacitor. The impedance of the IC port is lower than the target impedance no matter where the decoupling capacitor is placed in this region. To optimize specific capacitor placements in this region, the Newton iteration, based on the Hessian matrix, is used to determine the location where the impedance of the IC port is minimized at the antiresonant frequency of the plane pair. This placement optimization algorithm allows for a decoupling design method that can also be applied to a PDN with multiple decoupling capacitors for multiple IC ports. Compared with the method of random selection from within the effective decoupling area, the method proposed here requires fewer decoupling capacitors and less computational time.

The Simulated TDR Impedance In PCB Material Characterization

Abstract: High-speed PCB design for signal integrity (SI) is about feasible material selection, trace geometry determination and optimization of discontinuities, where the accurate PCB material characterization is essential since incorrect material properties may lead to misleading results and wrong design descisions. The previous studies have revealed that the simulated time-domain reflectometry (TDR) impedance in material characterization, which is based upon the transmission-line-based methods, is erroneous when compared to the measured value, although a good agreement between simulation and measurement in the frequency domain can always be reached. In addition, it is also shown that achieving a satisfactory correlation in both transmission phase and trace impedance is a challenge for SI engineers. This implies that the transmission-line-based approaches, which are widely used in industries, are not perfect and that the extracted PCB material properties are not accurate enough. In this paper, a step-by-step investigation is performed and demonstrated to disclose the root causes of the TDR impedance discrepancy. It is found that the disagreement in TDR impedance is contributed by multiple factors which need to be taken into consideration during material characterization. The improved simulation result exhibits excellent consistency with the measured trace impedance. The suggestions to hardware designers on how more accurate PCB dielectric properties can be obtained are given by addressing the TDR impedance discrepancy issue.

Far-End Crosstalk Analysis for Stripline with Inhomogeneous Dielectric Layers (IDL)

Abstract: Far-end crosstalk (FEXT) noise is a critical factor that affects signal integrity performance in high-speed systems. The FEXT level is sensitive to the dielectric inhomogeneity of the stripline in fabricated printed circuit boards (PCB). Stripline is typically modeled as a 2-layer model with core and prepreg layers. However, in reality, the stripline is laminated by multiple inhomogeneous dielectric layers (IDL). The dielectric layers of the stripline are laminated with epoxy resin and glass bundles. The dielectric permittivity (e r ) of the epoxy resin and glass bundles are different, which causes the inhomogeneity of the dielectric layers while also increasing the FEXT magnitude. Therefore, a typical 2-layer structure is inaccurate to model the FEXT. In this paper, the stripline model is constructed with the core, prepreg, and resin pocket layers. To analyze the stripline with three IDL, a practical superposition method is proposed. A design guideline to mitigate the FEXT level in the stripline design is proposed based on the method.

Topology-Based Accurate Modeling of Current-Mode Voltage Regulator Modules for Power Distribution Network Design

Abstract: Power distribution network (PDN) is essential in electronic systems to provide reliable power for load devices. Thus, modeling of PDNs in printed circuit boards and packages has been extensively studied in the past few decades. However, with the higher integration levels and operation bandwidths of modern voltage regulator module (VRM), there lacks an accurate model for transient load responses based on the widely used current-mode control topology. In this work, a topology-based behavior model, including both the power stage and control loops, is developed for the current-mode buck VRM. A novel method is also proposed to unify the modeling of the continuous and discontinuous conduction modes for transient load responses. Through the measurement-based characterization, the model parameters are optimized to match with the actual design. Furthermore, this model can be applied to both the time-domain and frequency-domain circuit simulations to predict the voltage droop and output impedance, respectively. The accuracy of the model is validated using an evaluation board containing the single-phase and multiphase VRMs. The proposed model for current-mode control VRM can be easily cascaded with other PDN components to enable a combined PDN analysis.

High-Frequency Modeling of Permanent Magnet Synchronous Motor Considering Internal Imbalances

Abstract: In this paper, an accurate high-frequency modeling methodology for a permanent magnet synchronous motor (PMSM) in a vehicular electrical braking system is presented, which is suitable for analyzing various electromagnetic interference problems caused by a motor drive system. The proposed modeling approach is established according to the vector fitting technique and based on the S-parameter measurements of the PMSM. The equivalent circuit model of the PMSM converted from a measured S-parameter matrix can better describe the impedance characteristics of the three-phase PMSM under study compared to the existing equivalent circuit models because the imbalances inside the motor are taken into account in the proposed modeling process. The proposed PMSM model exhibits high accuracy in the range from 100 kHz to 120 MHz in comparison with the common-mode and differential-mode characteristics of the PMSM, which are measured using the conventional setups.

Far-End Crosstalk Control Strategy for High-Volume High-Speed PCB Manufacturing: The Concept of Critical Resin Content Percent

Abstract: Far-end crosstalk (FEXT) can reduce the eye opening and eventually decrease the maximum data rate that can be transmitted through the high-speed interconnections. Therefore, FEXT is an important concern in high-speed digital design. The contributors of stripline FEXT include the dielectric inhomogeneity and the proximity effect. In addition, a characterization technique for the effective relative dielectric constant (Dk) of both core and prepreg has been proposed recently for the analysis of the inhomogeneous medium and induced FEXT. In our study, the FEXT levels of the striplines on various printed circuit boards (PCBs) are measured and compared. It is brought to our attention that for some PCB striplines sharing the same stack-up, same PCB material, and manufactured by the same vendor, the corresponding measured FEXT magnitudes of these coupled single-ended traces could vary drastically, which may bring great challenges to the hardware engineers about FEXT level control during the high-volume PCB production phase. In this paper, the root cause of this issue is investigated and analyzed. The “critical resin content percent” concept is proposed to explain the variations in the Dk values of prepreg that result in the FEXT level variance. The full wave simulations are conducted to identify the “critical glass weave”. A measurement-based statistical analysis is performed to verify the “critical resin content percent” concept. A design guideline for FEXT control strategy in the high-volume PCB manufacturing is presented based upon this investigation.

Gassian Process Regression Analysis of Passive Intermodulation Level and DCR for Spring Contacts

Abstract: In modern consumer electronic devices, for the purpose of having easier access for assembly and repair in a compact designed product, metallic connection components such as springs are universally used for metallic connections between modules or chassis. However, the non-ideal metallic connections tend to have a certain level of non-linearity. Therefore, significant attention has been aroused recently because the passive-intermodulation (PIM) can degrade the radio-frequency (RF) antennas’ receiving quality especially when the unsatisfying spring connections are placed near the RF antenna. Typically, advanced and expensive instruments and components are required to estimate the non-linearity levels of the springs. However, those instruments are usually not available for the manufacturing factories for massive tests. This paper is focused on investigating the feasibility of estimating the nonlinearity level of spring contacts using DC resistance (DCR), which has easier access to be tested with much lower cost. Study showed that the DCR, when under certain conditions, can serve as the alternative figure of merit for PIM prediction. Then, the Gaussian process regression (GPR) analysis based on measured data can provide a statistical estimation to the generated PIM from the DCR values.

Self-contact Introduced Passive Intermodulation Characterizations for Captured Springs

Abstract: Passive intermodulation (PIM) is one of the most common nonlinear behavior that exists in a variety of applications. Nowadays, consumer electronics designs use a variety of mechanical features for radio-frequency (RF) antenna feeds and grounding, such as springs, gaskets, screws, etc. When these components are placed in the path or nearby the RF antennas, the unsatisfying connection such as loose contact will generate PIM and create noise in the receiving frequency range. This can potentially cause RF desense issues. In product design, the most intrinsic method to improve the electrical connection is applying more compression between the spring tip and the landing substrate, but seldom will the engineers notice the spring structure itself can also introduce a lot of PIM. This paper concentrates on characterizing and validating the captured RF springs that can introduce noticeable PIM due to its structural self-contact phenomenon. An integrated camera recorded the spring side-view under compression. The measured information indicates that high PIM tends to occur when the spring contacts itself unintentionally.

EMI Investigation and Mitigation of Flexible Flat Cables and Connectors

Abstract: In modern mobile devices, as a result of the increase in data rate, requirement for higher density signal and cost-effective solution, the flexible flat cable (FFC) now plays an important role to connect separated printed circuit boards (PCBs). Due to the low-cost fabrication and varied shielding structure, FFC has been identified as a noise source for electromagnetic interference (EMI) and desense issues. In this paper, the common mode noise generated from FFC and related connectors is investigated. With the assistance of full wave and circuit simulation, main cause of the common mode noise has been identified as the ground discontinuity and the related voltage difference between the PCB ground and the FFC ground. By providing better shielding and improving ground continuity, 11 dB reduction of total radiation power (TRP) is observed at 5 GHz.

Time Domain Continuous-Time Model of Current Mode Buck Converter for Power Delivery Network Design

Abstract: Proper power integrity (PI) analysis is essential for modem electronics devices to minimize voltage noise. The low- frequency response of a power distribution network (PDN) is determined by the voltage regulator modules (VRMs) installed on the board. However, the conventional VRM model is either represented by an over-simplified passive circuit or an encrypted model provided by then vendor. These models can only work for limited operating conditions. In this paper, a generic average model for up-to-date DC converter is proposed. Both time and frequency domain responses of a current-mode buck converter with adaptive on-time control (AOT) method are captured by the proposed model. This cycle-by-cycle averaged model can be extended for converters with other control methods.

Root Cause Analysis for the Phase Noise of the Clock Generator

Abstract: The performance of the high-speed links in the electronic system is highly dependent on the quality of the clock signal, which can be quantified by phase noise. The phase noise represents the instabilities of the signal in the frequency domain by measuring the power at various offsets from the carrier frequency. The root cause for the phase noise of the clock output at the resonance frequency is analyzed and identified in this paper. The power supply, the heat sink, and the external crystal are the main sources of the phase noise. Spurious occurs at the frequency of the power rail in the measured phase noise. The heat sink over the chip induces the conductive coupling noise to the clock. The low-frequency bump in the phase noise plot turns out to be induced by the external crystal design of the clock. More attention should be paid to the ground routing of the external crystal to ensure the quality of the clock output.

Estimating Electromagnetic Emissions from a Site Installation with Multiple Racks of Server Equipment

Abstract: More than hundreds, sometimes even thousands, of servers operate simultaneously inside a data center. Their radiation can be a problem and cause electromagnetic interference (EMI) issues. However, it is not feasible to perform full-wave 3D simulation of these racks because of the large electrical size of the model. In this paper, an algorithm is proposed to predict the emission from rack arrays. The equivalent dipole source is extracted from EMI measurement data of a single rack and reconstructed as a radiation source in a multiple rack model. The racks in an array can be divided into a few categories and the racks in each category have similar radiation patterns. Thus only one modeling of a representative rack is needed for each category. In order to take rack to rack scattering into consideration, a simplified model for each category is developed and method of moments is used to describe the radiation of representative racks. After the radiation calculations from a representative rack in all the categories are completed, the total radiation from the data center is predicted based on these representative-rack calculations. This method is much faster than the brute-force simulation of the entire data center, and is highly scalable to handle arbitrary number of racks in the data center.

Reduction of Mode Conversion of Differential-Mode Noise to Common-Mode Noise by Printed Circuit Board Modification for Unbalanced EMI Filter Network

Abstract: This paper presents a method for the reduction of mode conversion from differential-mode (DM) noise to common-mode (CM) noise in an unbalanced EMI filter. The unbalanced nature in the EMI filter is a result of not incorporating all the required filter components due to space and cost constraints or due to the parasitic impedances of a printed circuit board (PCB). It is demonstrated that the reduction of mode conversion from DM noise to CM noise can be achieved by modifying the current path on the ground (GND) layer of the PCB of the unbalanced EMI filter. The currents on the GND layer are guided to take a longer route by introducing a "cutout" to the ground plane in the PCB, which increases the impedance of the current path on the GND layer. This approach does not require additional components to the EMI filter for the reduction of CM noise due to the mode conversion. Simulations show that the cutout decreases the CM noise converted from the DM noise by at least 4 dB in the AM radio frequency band (530 kHz – 1.8 MHz).

High-Frequency Electromagnetic Interference Diagnostics

Abstract: Electromagnetic interference (EMI) is becoming more troublesome in modern electronic systems due to the continuous increase of communication data rates. This chapter reviews some new methodologies for high-frequency EMI diagnostics in recent researches. Optical modules, as a typical type of gigahertz radiator, are studied in this chapter. First, the dominant radiation modules and EMI coupling paths in an explicit optical module are analyzed using simulation and measurement techniques. Correspondingly, practical mitigation approaches are proposed to suppress the radiation in real product applications. Moreover, an emission source microscopy (ESM) method, which can rapidly localize far-field radiators, is applied to diagnose multiple optical modules and identify the dominant sources. Finally, when numerous optical modules work simultaneously in a large network router, a formula based on statistical analysis can estimate the maximum far-field emission and the probability of passing electromagnetic compatibility (EMC) regulations. This chapter reviews a systematic procedure for EMI diagnostics at high frequencies, including EMI coupling path analysis and mitigation, emission source localization, and radiation estimation using statistical analysis.