Boost Your Capabilities in Signal Integrity Analysis
Embarking on the journey of signal integrity (SI) analysis in the PCB design workflow is an essential step towards creating robust and high-performance electronic systems. This process involves integrating several key steps, from pre-layout planning to post-layout validation, supported by advanced simulation tools and measurement techniques.
Pre-layout Analysis and Design Guidelines
The initial phase of the workflow focuses on early-phase analysis and design guidelines. Critical signal path details, controlled impedance routing, differential pair length matching, and layer stack-up configurations are defined to establish proper line impedances. Minimizing the use of vias and optimizing via impedance, grouping signal traces appropriately, and designing component/connector pads to match impedance requirements set the foundation to avoid signal integrity problems later in the design.
Post-layout Simulation and Evaluation
Upon completion of the design, signal integrity simulation tools like Sigrity X, Ansys SIwave, and Keysight ADS are employed to analyze the design's signal behavior. These tools model real-world factors such as reflections, crosstalk, jitter, and ground bounce, using methods like IBIS, SPICE, and S-parameters. Simulating the signal eye diagram ensures the signal is clean and the eye-opening is sufficient to avoid data errors. Correction measures are proposed when simulations reveal degradation.
Measurement and Validation
Physical measurements using Time Domain Reflectometry (TDR) and Vector Network Analyzers (VNA) validate the simulation results, catching real-world parasitic effects and verifying the impedance control and return path optimization.
Co-simulation for Signal and Power Integrity
Combining signal and power integrity simulations helps consider simultaneous switching noise and voltage fluctuations affecting overall signal quality. AI-enhanced SI prediction is emerging to further optimize the workflow and accuracy.
Workflow Integration and Tool Synergy
Employing integrated design environments like Sigrity X within PCB CAD platforms (e.g., Allegro X) enables seamless in-design SI/PI analysis. This workflow-driven approach allows designers and SI engineers to perform iterative checks early and often, preventing costly late-stage fixes.
The Keysight EDS PCB design tool is one such platform that supports this holistic approach. It includes features like a RapidScan process for impedance analysis, which involves importing the board, selecting HDMI nets, and performing a RapidScan-Z0 analysis. The images show that the expected and the resultant values of S parameters are consistent for low and high frequencies, indicating the tool's accuracy.
A High-Speed PCB Design Guide is also a valuable resource, containing explanations of signal integrity issues, understanding transmission lines and controlled impedance, and high-speed layout guidelines.
In summary, unlocking signal integrity potential means embedding SI-aware design practices from the start, employing rigorous simulation before and after layout, validating with real measurements, and using integrated toolchains to streamline the entire process. This holistic approach ensures robust high-speed PCB designs capable of meeting demanding performance criteria. The channel simulation uses a PRBS (pseudo-random binary sequence) to evaluate the signal integrity, and transient analysis is a key aspect for ensuring signal integrity in the design. The comparison between the expected eye diagram and the simulation data shows an open eye, indicating consistency.
A comprehensive impedance calculator, such as the one available within the Keysight EDS PCB design tool, aids in determining the proper line impedances during pre-layout planning. In post-layout simulation and evaluation, signal integrity simulators like Sigrity X, Ansys SIwave, and Keysight ADS are utilized to analyze the design's signal behavior, accounting for real-world factors like controlled impedance and data-and-cloud-computing technology.
