Analysis Of The Electromagnetic Radiation In High-Speed Printed Digital Circuits Boards

The rapid increase of clock speeds in digital circuits is placing new requirements on the impedance of power supply systems .Wavelengths of clock harmonics are becoming comparable with dimensions of power supply planes used in multi-layered PCBs. Resonant modes associated with PCB dimensions, which previously were of no concern , are now appearing within the frequency spectrum of modern logic families.Power supply planes not only provide DC voltage to digital circuits, but also serve as a reference potential for switching. Any noise or ringing on the supply planes compromises signal integrity and reduces the reliability of the circuits. Such ringing also degrades the circuit's immunity to external electromagnetic disturbances and increases its emission, especially when resonance occurs, the electromagnetic radiation of PCBs is the most important! It is very bad to increase the products' EMC. So, it is very significative how to predict fast direct radiation from the power supply system of their printed circuits boards. In the paper first of all, the high-frequency behavior of the capacitor which widely employed is analyzed combined with the simulation of power integrity (PI), and then we introduced the SPICE models for both Ta-capacitors and ceramic capacitors with Monte Carlo Method. It then present the equivalent flux method to predict common mode radiation and power ground planes resonance based on circuits analysis and 2-dimensional transmission line theories. The methods are also verified by full wave electromagnetic field analysis, plane model simulation. The approach simplifies the complicated modeling and simulation process of using 3D full wave field solver, while still produces good results.