PCB Trace Impedance Measurement via Built-in Test Circuitry
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Solution Overview
Problem
Current methods for verifying trace impedance on printed circuit boards (PCBs) in information handling systems are costly, time-consuming, and prone to human error, often requiring disassembly and only validating a few samples, which can lead to signal integrity issues and functional failures due to poorly controlled trace impedance.
Innovation Solution
Implementing built-in test trace circuitry and programmable integrated circuits that enable automatic impedance measurement and tuning on fully assembled system level boards, allowing for remote verification of trace impedance without disassembly, thereby quickly identifying and correcting signal integrity issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TDR machines are used to measure trace impedance, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses built-in test circuitry within the information handling system itself to perform impedance measurements, eliminating the need for external TDR machines. The processor and associated circuitry serve dual purposes: normal system operation and impedance measurement, achieving self-service functionality.
Solution Approach 2:
The patent introduces test circuitry as an intermediary component that enables impedance measurement without requiring complex external equipment. This test circuitry acts as a mediator between the processor and the measurement function, simplifying the overall measurement system.
2Measurement precision
If manual TDR measurement processes are used, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The system performs automatic self-testing of trace impedance without requiring manual intervention. The processor automatically executes measurement routines, eliminating the need for operators to manually connect and operate external TDR equipment, thereby significantly increasing measurement productivity.
Solution Approach 2:
The impedance measurement can be performed continuously or periodically during system operation without interrupting normal functionality. The test circuitry operates seamlessly alongside the main system, allowing for continuous verification of trace impedance across multiple PCBs.
3Loss of time
If only a few PCB samples are tested, then measurement time is reduced, but reliability decreases
Solution Approach 1:
Each PCB performs its own impedance measurement independently through built-in test circuitry. This eliminates the bottleneck of manual testing where only a few samples can be measured sequentially, allowing for rapid parallel verification of multiple PCBs while maintaining full measurement capability.
Solution Approach 2:
The test circuitry is pre-integrated into the PCB design, allowing impedance measurements to be performed at any stage during manufacturing or operation. This preliminary preparation of measurement capability enables rapid quality verification without adding post-manufacturing complexity.
4Measurement precision
If PCB disassembly is required for measurement, then measurement precision is improved, but ease of operation worsens
Solution Approach 1:
The measurement system is fully integrated within the assembled PCB, requiring no disassembly or external equipment connection. The built-in test circuitry enables measurements to be performed on the complete assembled board, making the process as easy as powering on the system and executing a measurement routine.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables faster and more cost-effective validation of PCB trace impedance, reducing debug time and improving the robustness of high-speed signal-enabled information handling systems by allowing for quick identification and correction of signal integrity issues.
Implementation Method 1
provide a voltage pulse from the second electrically conductive signal path through the source impedance (ZS) and first node to the first electrically conductive signal path, and then sample multiple voltage values over time at a third node positioned between the source impedance (ZS) and the first impedance while the voltage at the third node is responding to a voltage waveform created by the voltage pulse
Implementation Method 2
PCB trace impedance plays a critical role in the integrity of high-speed electrical signal waveforms on system level boards used in information handling systems. Reflections will occur during system operations if the trace impedance does not match the source impedance
Data Source
AI summary
Systems and methods that may be implemented to provide on-board trace impedance testing for a system level board of an information handling system. A printed circuit board (PCB) of the system level board may include built-in test trace circuitry that may be used to measure board trace impedance so that the trace impedance of a fully assembled system level board may be tested and verified for compliance with trace impedance specification, and without requiring any disassembly of the board.