Electromagnetic characterisation of printed circuit boards

在开发由快速时钟驱动的电路方面取得了重大进展，从而大大提高了处理速度。现在可以使用几GHz的时钟频率。即使是时钟频率的几个谐波，也可以使设计很好地进入微波区域，其中印刷电路板（pcb）具有几个波长的尺寸，并成为电磁（EM）能量的有效辐射体。时钟速度的提高与器件开关电压水平的降低相结合，使下一代系统中的发射和易感性成为关键问题。在高速系统的设计阶段，尽早将电磁兼容性（EMC）纳入其中变得至关重要。设计工程师主要关注基于电路的电流和电压，通常只略微意识到EMC问题。EMC主要关注设备的电磁场发射以及设备对外部电磁场的敏感性。电磁场驱动的问题使得电路几何形状以及网络连接对于电较大（与波长相比）的pcb很重要。pcb也变得越来越复杂，因此量化它们的电磁特性变得更加困难。当然，通过详细的3D电磁模拟，可以精确地再现PCB周围的电磁场，但这需要不切实际的计算能力和模拟运行时间。基于全现场的工具，虽然为微波电路发展得很好，但不能有效地处理现代设计的复杂性。EMC问题经常涉及工作频率之外的谐波频率，并且超出了设备特性精确量化的范围。提供高效的EMC CAD分析工具和概念将是对高级工程设计的及时补充。该项目的目的是尽可能简化PCB的电磁辐射问题，并为设计工程师提供一个简单连贯的PCB性能测量方法，可以在EMC分析包中插入和播放。通过这一点，我们的意思是一个简单和一般的发射当量的公式，它可以很容易地纳入到全场EM模型中，以评估几个pcb在其工作环境中的EMC相互作用。所提出的方法是响应已建立的IBIS方法，用于工程师熟悉的设备的端口表征。提出了开发和评估一种技术，其中PCB的电磁发射和耦合是由电偶极子和磁偶极子阵列表征的。PCB分割和等效偶极子表示的方式将是广泛调查的主题，因为它必须提供一种可接受的复制排放的方式。这些偶极子结构可以是主动的来表示板上源，也可以是被动的来表示PCB和EM环境之间的耦合。虽然PCB结构可能很复杂，但通常需要大约十分之一波长的分辨率才能准确地表示器件的EM特性。因此，一个相等的偶极子阵列，其源振幅和阻抗间距为几厘米，应该足以准确地表示PCB。理想情况下，这种表示必须在外壳或外部环境的系统条件的所有变化下保持不变。通过这种方式，开发工程师将拥有一个简单而高效的模型，该模型可以插入标准的电磁场求解器中，以快速实现EMC系统设计的原型。此外，现实问题可以在合理的计算成本下解决。所提出的PCB的电磁表示将非常强大，因为它将是完全通用的，不仅适用于全电磁场求解器，也适用于其他半解析的中间电磁兼容模型。这样的模型允许在概念设计阶段进行假设研究。

Significant advances have been made in developing circuits driven by fast clocks, thus increasing dramatically processing speeds. Clock rates of a few GHz are now available. Even a few harmonics of the clock rate, takes designs well into the microwave region where printed circuit boards (PCBs) have dimensions of the order of several wavelengths and become efficient radiators of electromagnetic (EM) energy. The increase in clock speed in combination with the driving down of device switching voltage levels is making emissions and susceptibility critical issues in the next generation systems. It is becoming critically important to include electromagnetic compatibility (EMC) very early in the design phase of high speed systems. Design engineers are primarily concerned with circuit based currents and voltages and are normally only marginally aware of the EMC issues. EMC is primarily concerned with the emission of EM fields from devices and the susceptibility of a device to an external EM field. EM field driven issues make circuit geometry as well as network connectivity important for PCBs which are electrically large (compared to wavelength). PCBs are also becoming more complex so that quantifying their EM properties is more difficult. It is of course possible, through detailed 3D EM simulation, to accurately reproduce the EM fields around a PCB but this requires unrealistic computing power and simulation run times. Full field-based tools, although well developed for microwave circuits, cannot deal efficiently with the complexity of modern designs. EMC issues are frequently concerned with harmonic frequencies outside the operating frequency and beyond the range for which device characteristics are accurately quantified. The provision of efficient EMC CAD analysis tools and concepts would be a timely addition to advanced engineering design.The object of this project is to simplify the problem of EM emissions from PCBs as much as possible and to provide design engineers with a simple coherent measure of the performance of a PCB, which can be plugged and played in an EMC analysis package. By this we mean a formulation of simple and general emission equivalents, which can easily be incorporated into full-field EM models for the purpose of assessing EMC interaction of several PCBs in their operating environment. The method proposed is to echo the established IBIS approach for the port characterization of devices which engineers are familiar with. It is proposed to develop and evaluate a technique where the EM emissions and coupling of a PCB are characterized by an array of electric and magnetic dipoles. The way the PCB is segmented and represented by equivalent dipoles will be the subject of extensive investigations as it must offer an acceptable way of replicating emissions. These dipole structures may be active to represent on board sources or passive to represent the coupling between the PCB and the EM environment. Though PCB structures may be complex, resolution of the order of approximately a tenth of a wavelength is normally necessary to accurately represent a device's EM characteristics. An array of equivalent dipoles spaced a few cm apart with their source amplitudes and impedances should, therefore, be sufficient to accurately represent a PCB. Ideally this representation must be invariant under all changes in system conditions in the enclosure or the external environment. In this way the development engineer will have a simple and efficient model, which can be plugged into standard EM field solvers to rapidly prototype a system design for EMC. Also, realistic problems can be tackled at a reasonable computational cost. The proposed EM representation of a PCB will be very powerful as it would be completely general being valid not only for full EM field solvers but also for other semi-analytic intermediate EMC models. Such models allow what if studies to be conducted during the conceptual design phase.