多层PCB 电源地平面返回路径阻抗的边界元分析

研究了多层印制电路板(PCB)中含有一个信号过孔的电源/地平面返回路径阻抗的频域特性,并分析采用添加短路过孔的方法减小多层PCB的输入阻抗.电源/地平面形成了径向传输线结构,反焊盘处的输入阻抗即为信号电流在电源/地平面间的返回路径阻抗.在电源/地平面外部边界施加PMC(完全导磁体)边界条件,在反焊盘处施加电流激励源,短路过孔轴向电场为零,采用高效的二维边界元法求解.计算了10GHz内电源/地平面返回路径的输入阻抗.结果表明:在两特性相同的平面之间添加短路孔可以降低输入阻抗,同时,电源、地平面的输入阻抗随频率变化交替呈现容性或感性,在反谐振频率处输入阻抗值可达几百欧姆,此外,在频率较低时输入阻抗可用静态电容或静态电感表示.采用基于全波分析的有限元软件验证了计算结果和计算方法的正确性.     

Improving signal integrity in circuit boards by incorporatingembedded edge terminations

Much attention has been paid toward signal and power integrity in devices, circuit boards and entire systems. Resonances set up between the power and ground planes due to multiple reflections from the edges of the circuit board will affect signal integrity. The impedance seen by a via passing between the power and ground planes can be very high at the resonant frequencies. This gives rise to the effects of crosstalk and simultaneous switching noise (SSN) which would adversely effect the operation of the device. An attempt has been made in this paper to cover all the topics in earlier papers (Shi et al., Proc. Electron. Comp. Technol. Conf., 2001, and Adsure et al., Proc. IPAC'01 Conf., 2001), which describe a method to incorporate lossy (absorbing) material at the edges of a circuit board to reduce the wave reflections. The "lossy material" is usually a material of very high resistivity but which shows large magnetic losses at UHF and microwave frequencies. Thus this material is suitable to be placed directly between the power and ground planes without introducing any DC leakage currents. Experiments were carried out on a bare copper circuit board with FR-4 dielectric. The absorber used in the experiments is available commercially in flexible, castable and hard dense forms. It is shown that it is possible to reduce the impedances at the resonant frequencies to quite an extent over a broad frequency band by applying the lossy material at the edges of the board. Various configurations of applying the material are also described     

The effect of test system impedance on measurements of groundbounce in printed circuit boards

Based on the 3D-FDTD approach, an efficient equivalent model employing the embedded resistive voltage source is proposed to simulate the effect of test system impedance on the measurement of the ground bounce noise for the power planes structure in the printed circuit boards (PCB). Compared with the measured results by vector network analyzer, this equivalent model well predicts the impedance behavior of the V_cc/GND power planes. The influences of different probe loading conditions of the test system on the measurement of impedance behavior are studied. It is found that the effects of the probing loads on the measurement of the ground bounce noise is significant at the frequencies near the dc point and resonance, but the influences of the probes are small at the frequencies far from resonance. In addition, the transfer characteristics of the power bus in the realistic digital circuits with decoupling capacitance being considered are simulated in the FDTD model. The difference of the transfer behavior between the realistic case without coaxial feed and the measured results with probing effects is also numerically compared. We find that the ground bounce noise in the real circuit can be accurately measured at most frequencies, where the power planes act in very low impedance, except at the frequencies near dc and resonance frequencies, where the power planes behave in relatively higher impedance characteristics     

Reducing simultaneous switching noise and EMI on ground/powerplanes by dissipative edge termination

Power and ground planes are required to have low impedance over a wide range of frequencies. Parallel ground and power planes in multilayer printed-circuit boards exhibit multiple resonances, which increase the impedance and also the radiation from the edge of the board. Resistive termination along the board edges reduces the resonance peaks. Simple and straightforward design expressions, simulated self and transfer impedances, as well as measured impedance plots are presented for power-ground planes     

Application of the cavity model to lossy power-return plane structures in printed circuit boards

Power-return plane pairs in printed circuit boards are often modeled as resonant cavities. Cavity models can be used to calculate transfer impedance parameters used to predict levels of power bus noise. Techniques for applying the cavity model to lossy printed circuit board geometries rely on a low-loss assumption in their derivations. Boards that have been designed to damp power bus resonances (e.g., boards with embedded capacitance) generally violate this low-loss assumption. This paper investigates the validity of the cavity model when applied to printed circuit board structures where the board resonances are significantly damped. Cavity modeling results for sample lossy power-return plane structures are validated using a three-dimensional full wave numerical code. A simple method is also established to check the validity of the cavity model for a power-return plane structure with imperfect conductors and lossy dielectric substrates.     

Reducing power bus impedance at resonance with lossy components

Power bus structures in printed circuit boards with solid power and ground planes exhibit resonances. When the power bus is resonant, the power bus impedance can increase dramatically. This paper explores the effect of component equivalent series resistance (ESR) on power bus resonances. General guidelines for selecting an optimum ESR are provided and are supported by laboratory measurements and numerical simulations.     

Estimating the noise mitigation effect of local decoupling in printed circuit boards

Local decoupling, i.e., placing decoupling capacitors sufficiently close to device power/ground pins in order to decrease the impedance of power bus at frequencies higher than the series resonant frequency, has been studied using a modeling approach, a hybrid lumped/distributed circuit model established and an expression to quantify the benefits of power bits noise mitigation due to local decoupling developed. In this work, a test board with a local decoupling capacitor was studied and the noise mitigation effect due to the capacitor placed adjacent to an input test port was measured. Closed-form expressions for self and mutual inductances of vias are developed, so that the noise mitigation effect can then be estimated using the previously developed expression. The difference between the estimates and measurements is approximately 1 dB, which demonstrates the application of these closed-form expressions in the PCB power bus designs. Shared-via decoupling, capacitors sharing vias with device power/ground pins, is also modeled as an extreme case of local decoupling.     

The development of a closed-form expression for the input impedance of power-return plane structures

In multilayer printed circuit boards, the noise on the power bus is influenced by the impedance between the power and ground planes. Power-bus noise estimates require an accurate estimate of the power-bus input impedance. This paper develops a closed-form estimate of the input impedance for circular power-return plane structures. When the structure is lossy (e.g., boards employing embedded capacitance or densely populated boards), the energy reflected from the board edge does not significantly affect the input impedance. In general, the expressions developed here for circular structures can be used to estimate the impedance of lossy power-return plane structures of any shape.     

Matrix substitution method for power bus analysis with isolated power island in high-speed packages and PCBs

We propose a matrix substitution method for analyzing a power bus containing a power island in high-speed packages and printed circuit boards (PCBs). The method is based on a segmentation method and a resonant cavity model for a rectangular cavity, and the impedance of the power bus containing the power island can be calculated analytically. Finally, the proposed method is verified by means of impedance measurements in the frequency domain.     

Electromagnetic interference (EMI) reduction from printed circuit boards (PCB) using electromagnetic bandgap structures

As digital circuits become faster and more powerful, direct radiation from the power bus of their printed circuit boards (PCB) becomes a major concern for electromagnetic compatibility engineers. In such multilayer PCBs, the power and ground planes act as radiating microstrip patch antennas, where radiation is caused by fringing electric fields at board edges. In this paper, we introduce an effective method for suppressing PCB radiation from their power bus over an ultrawide range of frequencies by using metallo-dielectric electromagnetic band-gap structures. More specifically, this study focuses on the suppression of radiation from parallel-plate bus structures in high-speed PCBs caused by switching noise, such as simultaneous switching noise, also known as Delta-I noise or ground bounce. This noise consists of unwanted voltage fluctuations on the power bus of a PCB due to resonance of the parallel-plate waveguiding system created by the power bus planes. The techniques introduced here are not limited to the suppression of switching noise and can be extended to any wave propagation between the plates of the power bus. Laboratory PCB prototypes were fabricated and tested revealing appreciable suppression of radiated noise over specific frequency bands of interest, thus, testifying to the effectiveness of this concept.     

Numerical and experimental investigation of radiation caused by the switching noise on the partitioned DC reference planes of high speed digital PCB

Influence of the partitioning and bridging of the power/ground planes on the radiation caused by the switching noise on the dc reference planes is investigated both theoretically and experimentally. Based on the three-dimensional finite-difference time-domain modeling, the electromagnetic interference (EMI) performance of the partitioned power/ground planes is studied. Radiated emission at the 3-m distance from the tested boards is measured in a fully anechoic chamber. The measured and the numerical results agree generally well. The radiation behavior of four kinds of partitioned configuration of the power/ground planes is studied. It is found that completely isolating the noise source by the etched slits, or moats, significantly reduces the radiation level at the frequencies near resonance. However, bridges connecting two sides of the moat not only significantly degrade the ability of the EMI protection of the moat, but also excite a new low-frequency resonant mode. The effect of the geometrical parameters, such as the moat size, moat location, bridge width, and bridge position, on the radiation behavior of the printed circuit board is considered. The radiation mechanism of the EMI behavior of the partitioned dc reference planes is discussed.     

过孔转换信号完整性分析的区域分解有限元法

提出了一种基于区域分解的二维有限元法分析多层印制电路板电源/地平面中过孔转换结构的信号完整性.过孔电流产生的电磁场呈三维结构,其中,一部分电磁波沿过孔轴向传输,另一部分电磁波在电源/地平面间沿径向传播.采用一虚拟柱面将求解区域分割为过孔区和电源/地平面区.将过孔区建模为以周向磁场为主分量的二维轴对称问题,而将电源/地平面区建为以垂直电场为主分量的二维模型.首先求解电源/地平面区的二维边值问题获得分割边界上节点的波阻抗,然后将该波阻抗代入过孔区模型中分割边界节点的边界条件,从而计算出过孔信号传输的S参数.所提方法通过模型缩减可实现对微细过孔结构信号完整性的精确快速计算,且采用全波电磁场分析软件对算法的有效性和准确性进行了验证.     

Hybrid analytical modeling method for split power bus in multilayered package

As multiple chips are being integrated into a single package with increased operating frequency, switching noise coupling on power buses has become an important design issue. To reduce the noise coupling, a split power bus structure has been generally used in package substrates having multilayered power and ground planes. Consequently, there is an increasing need for an efficient method to analyze a split power bus in a multilayered package. This paper introduces a hybrid analytical modeling method for characterizing a split power bus in a multilayered package. The proposed method uses a resonant cavity model combined with a segmentation method. Furthermore, a port assignment technique and an associated calculation method for the equivalent circuit model parameter of the split gap are proposed. The proposed port assignment technique and the analytical equation make it possible to analyze a split power bus, especially in a multilayered package. To verify the proposed method, multilayered test packages are fabricated and tested by means of frequency-domain measurements. In addition, an optimal power bus design method was successfully demonstrated for suppressing noise coupling between chips on a single package. Finally, the proposed method and optimal power bus design method was verified using a series of frequency-domain and time-domain measurements.     

Microwave measurement of temperature and current dependences ofsurface impedance for high-Tc superconductors

Perturbation formulas for TE₀₁₁-mode dielectric rod resonator and for a TE₀₁₁-mode circular cavity resonator are derived to determine the surface impedance Z_s of superconductors from measured values of resonant frequencies and unloaded Q. The relation between the maximum surface current density of a superconductor, J_s, and output power from a signal generator is derived. On the basis of these analytical results, a measurement technique is proposed to evaluate the temperature and J_s dependencies of Z_s for superconductors. The measured results of the temperature dependence of Z_s for YBCO and copper plates are presented. From these results, it is verified that the dielectric resonator is suitable for measuring the surface reactance for YBCO. From these Z_s values the temperature dependences of the skin depth and the penetration depth and those of the complex conductivity are obtained on the basis of the two-fluid model. These measured values agree well with the theoretical curves     

Modeling and Measurement of Radiated Field Emission From a Power/Ground Plane Cavity Edge Excited by a Through-Hole Signal Via Based on a Balanced TLM and Via Coupling Model

A balanced transmission line model (TLM) and via coupling model is proposed for efficient simulation of radiated field emission from a power/ground plane cavity edge, where the radiated field emission is excited by a through-hole signal via in a multilayer package and printed circuit board (PCB). The radiated field emission is simulated and measured with a series of test boards. The simulation agrees fairly well with the measurement confirming the preciseness and usefulness of the proposed model. It is shown that the through-hole signal via is a considerable source of the radiated field emission as well as the signal loss. When the signal trace is switching vertically stacked reference planes, the signal return current path is disconnected at the via and the impedance becomes extremely high. A significant amount of insertion loss and radiated field emission is generated at resonance frequencies of the plane cavity. The effect of a decoupling capacitor fence (De-Cap Fence) at the edge of the board to mitigate the radiated field emission is examined. The proposed model confirms that the De-Cap Fence changes the resonance mode and frequency of the plane cavity, and reduces the radiated field emission     

A bandwidth enhancement technique for mobile handset antennas using wavetraps

A novel technique for enhancing the impedance bandwidth of wireless terminal antennas is presented. By introducing resonant short circuit transmission lines to the long sides of the chassis edges, an effective electrical shortening of the terminal ground plane is achieved. This effect has been used to realize terminal ground planes with resonant lengths at high frequencies, such as GSM 1800/1900 MHz or UMTS 2 GHz, thereby extending the impedance bandwidth. The proposed technique has been validated by simulations and measurements. Three typical applications are presented where the introduction of wavetraps improves the bandwidth and/or in-band performance.     

谐振腔本征值问题的多极理论分析

本文给出用多极理论分析谐振腔本征值问题,以及用多极理论分析谐振腔本征值问题的使用规则。通过数学分析,导出用多极理论分析谐振腔本征值问题的计算公式。实例计算结果表明：用多极理论分析谐振腔本征值问题不仅具有较高的计算精度,而且可方便地应用电磁工程问题的设计与计算,是一种有效的谐振腔本征值问题分析方法。     

EMI mitigation with multilayer power-bus stacks and via stitchingof reference planes

General methods for reducing printed circuit board (PCB) emissions over a broad band of high frequencies are necessary to meet EMI requirements, as processors become faster and more powerful. One mechanism by which EMI can be coupled off a PCB or multichip module (MCM) structure is from high-frequency fringing electric fields on the DC power and reference planes at the substrate periphery. An approach for EMI mitigation by stitching multiple ground planes together along the periphery of multilayer PCB power-bus stacks with closely spaced vias is reported and quantified in this paper. Power-bus noise induced EMI and coupling from the board edges is the major concern herein. The EMI at 3 m for different via stitch spacing and layer thickness is modeled with the finite-difference time domain (FDTD) method. Design curves and an empirical equation are extracted from a parametric study to summarize the variation of the radiated EMI as a function of layer thickness and stitch spacing     

Power bus isolation using power islands in printed circuit boards

Power islands are often employed in printed circuit board (PCB) designs to alleviate the problem of power bus noise coupling between circuits. Good isolation can be obtained over a wide frequency band due to the large series impedance provided by the gap between the power islands. However, power bus resonances may degrade the isolation at high frequencies. The amount of isolation also depends on the type of connection between power islands and the components on the board. This paper experimentally investigates the effectiveness of several power island structures up to 3.0 GHz     

用时域有限差分法研究圆柱形谐振器

本文建立了圆柱坐标系下的时域有限差分(FD-TD)算法程序。运用算法分析了几种圆柱形谐振器(包括同轴形,圆柱形介质加载和开放式柱形介质谐振器)在各种模式下的谐振频率。数值结果与理论值、实验值进行了比较,表明具有很高的精度。本文还对计算中网格的选取原则进行了探讨;并计算了一种双层介质加载腔的谐振频率,从中得出一些有益的结论。