PCB Trace Characterization via Mixed-Mode S-Parameters
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Solution Overview
Problem
Current methods for measuring high-frequency electrical characteristics of printed circuit board (PCB) traces are time-consuming, expensive, and lack mathematical rigor, particularly for determining characteristics beyond signal loss, which is essential for high-speed data communications.
Innovation Solution
A method utilizing two-port measurements, assuming reciprocity and symmetry, and converting to mixed-mode s-parameters to characterize PCB traces, allowing for the determination of trace impedance, loss, and electrical length, with optional single-ended conversion and refinement through least-squares fitting to ensure measurement quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional methods are used to measure high-frequency electrical characteristics, then measurement precision is improved, but measurement time and cost increase significantly
Solution Approach 1:
The patent segments the measurement process into two independent parts: measuring the test structure (including known termination) and measuring the complete path (trace plus termination). By separating the unknown trace characteristics from the known termination characteristics, the method enables faster calculation through algorithmic processing rather than direct complex measurement of the trace alone.
Solution Approach 2:
The patent introduces a test structure with known termination as an intermediary element. Instead of directly measuring the trace (which is difficult and time-consuming), the method measures the test structure and complete path, using the known termination characteristics as a mediator to calculate the unknown trace characteristics through mathematical relationships.
2Measurement precision
If traditional measurement equipment is used, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent creates a simplified measurement model that copies the essential characteristics needed for trace analysis. Instead of using complex equipment to directly measure trace properties, the method uses a test structure with known termination that replicates the trace's electrical behavior in a controllable manner, allowing simpler equipment to extract the necessary information through algorithmic processing.
Solution Approach 2:
The patent changes the measurement approach from directly measuring trace electrical characteristics to measuring scattering parameters (S-parameters) of the test structure and complete path. This parameter transformation enables the use of simpler, more familiar measurement equipment while maintaining measurement precision through mathematical conversion of the parameters.
3Productivity
If SE2DIL method is used, then measurement speed is improved, but measurement precision for characteristics beyond loss deteriorates
Solution Approach 1:
The patent extends the measurement approach to be universal, using the same test structure and measurement process to extract multiple trace characteristics (impedance, loss, delay) simultaneously. By measuring both the test structure and complete path, the method can calculate various characteristics through different mathematical relationships, making the process multi-functional rather than limited to single-parameter measurement.
Solution Approach 2:
The patent employs iterative calculation with refinement feedback. The initial calculation uses measured S-parameters and known termination characteristics to compute trace characteristics. The method then allows for refinement by comparing calculated values with expected ranges and adjusting calculations, providing feedback that improves measurement precision while maintaining speed.
Data Source
AI summary
A method is provided which measures PCB trace characteristics from measurements of a PCB trace structure.