Applying FSV to the Comparison of Return Path Integrity in High Speed Circuit Designs

To ensure good signal integrity design, there are a number of design principles that should be applied, including avoiding any breaks in a current return path, e.g., a ground plane in a multilayer stack up. Occasionally, these guidelines are not followed: possibly through necessity or convenience. However, it is helpful to the designer to understand the impact of such factors that might influence the quality of the digital signal being transmitted. Typically, such an analysis might be undertaken using eye diagrams but it is more difficult to perform comparative testing on single transitions. This letter applies the FSV method, using the modified transient analysis approach, to single transitions for a PCB track having its return path influenced by a break in the return plane; in this case, the break is a circular `gap' in the ground plane. FSV's global difference measure is used to quantify the effects of the amount of overlap of the signal track with the gap. The paper illustrates how the modified transient FSV approach can help provide quantified supporting information for the SI designer.