Issue link: https://resources.pcb.cadence.com/i/1534337
To ensure that design decisions align with project goals and are achieved within acceptable parameters—including time, physical constraints, and electrical efficiency—these features and specifications must be systematically captured. Constraint management in OrCAD X Capture addresses this need with a robust library of constraints that are seamlessly integrated into the design process. This empowers engineers to develop PCBs with confidence, knowing that they will meet product goals. Moreover, if a product or PCB falls short, the constraints framework facilitates troubleshooting by identifying the root cause of the issue and potential solutions. High-Speed Design Problems in Practice High-speed PCB design requires more than just placing components and routing traces—it involves managing complex electrical phenomena that emerge at high frequencies (> 1 Gbps) and managing the time flow of signals, while maintaining signal integrity. Below are the primary high-speed design issues you may encounter and a quick overview of how OrCAD X provides practical solutions for each one. 1. Impedance Discontinuities Impedance discontinuity from routing causing signal reflections and ringing f Problem: When a signal encounters abrupt changes in impedance, such as through vias, connectors, or trace width changes, reflections occur. These reflections can cause signal distortion, including ringing and waveform degradation. f Solution: Speak with your manufacturer to determine their exact controlled impedance capabilities and boards for your high-speed designs. Maintaining proper impedance is of paramount importance. f Tips: Use impedance-controlled routing for critical high-speed signals, such as differential pairs, and verify performance through its built-in signal analysis tools. In high-speed PCB design, controlling impedance is critical to maintaining signal integrity. When the impedance of a signal path varies, it causes reflections that degrade the quality of the signal, leading to issues like ringing, overshoot, and data errors. Here, we'll explore common causes of impedance discontinuities, and how OrCAD X helps to manage and mitigate them effectively. Common Causes of Impedance Discontinuities Impedance mismatches are introduced when the geometry or environment of a signal trace changes abruptly. Some typical scenarios include: 1. Layer Transitions through Vias: f Problem: When a high-speed signal transitions between layers through a via, the change in surrounding material (e.g., from trace to via barrel) alters the impedance, resulting in reflections. f Solution: Use controlled impedance routing settings and set up design rules for via impedance. The Constraint Manager allows you to specify via geometries and layer transitions that minimize impedance disruptions. 6 www.cadence.com OrCAD X High-Speed Digital Design Guide