Amplify Your Capabilities in Signal Integrity Assessment
Effective signal integrity (SI) analysis in Printed Circuit Board (PCB) design is crucial for reliable high-speed signal transmission without distortion or data errors. Here's a step-by-step process that combines careful design, simulation, and verification.
1. Identify Critical Signals
Identify the signals requiring strict SI considerations, typically high-speed data lines, clocks, or differential pairs.
2. Specify Required Impedance
Define the target impedance, such as 50Ω for single-ended signals or 90Ω for differential signals, based on signal standards and application needs.
3. Design Trace Geometry and PCB Stack-up
Optimize trace width, thickness, and spacing while selecting proper dielectric materials with stable permittivity. Design the PCB layer stack-up to achieve the desired controlled impedance and support return current paths, minimizing crosstalk and electromagnetic interference.
4. Minimize Disruptive Elements
Reduce the number of vias, optimize via impedance, avoid sharp bends or stubs in traces, and carefully route differential pairs maintaining tight coupling and matched lengths.
5. Simulation and Pre-Layout Analysis
Use SI simulation tools to predict signal behavior, validate impedance control, and identify potential problems before finalizing the design. This can be done using time-domain reflectometry or eye diagram simulation.
6. Post-Layout Verification
After routing, perform SI analysis on the completed design to measure signal quality, checking eye diagrams and verifying impedance consistency, ensuring the signals meet performance criteria at the receiving end.
7. Manufacturing and Testing
Control manufacturing processes to maintain impedance specifications, then validate with physical measurements such as TDR or vector network analyzers to ensure real-world signal integrity matches simulation predictions.
In addition, the differential impedance can be calculated using a simple rule of thumb: if the width over the minimum (H1, H2) is about 1 and the spacing is around 3W, the differential impedance is equal to 100 ohms. To anticipate signal loss, loss metrics can be manually calculated, and to verify the calculated values, a 2D RapidScan can be performed using Keysight EDS.
The high-speed PCB design guide provides explanations of signal integrity issues, understanding transmission lines and controlled impedance, and high-speed layout guidelines. The expected time delay for a 3-inch trace in FR4 is about 0.5 nanoseconds, using a signal speed of 6 inches/nanosecond in FR4. The simulation considers a net, such as the signal flowing from the CPU (transmitter) to the HDMI retimer. The HDMI traces' stack-up states that H1 is 3 mils and H2 is 2.9 mils.
Use an impedance calculator to determine the differential impedance of a trace based on its width and spacing, such as 1 time the width and 3 times the spacing equating to a differential impedance of 100 ohms.
To ensure accurate signal loss predictions, manually calculate loss metrics and verify them using a 2D RapidScan with Keysight EDS, a technology for data-and-cloud-computing that aids in high-speed PCB design.
