RF PCB Impedance Testing via Intermediate Node Reflection
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Solution Overview
Problem
Conventional testing methods for radio frequency (RF) printed circuit boards are inefficient and costly, particularly in mass production, as they rely on radiated testing which is sensitive to surroundings and fails to accurately detect antenna and matching circuit issues, and require expensive network analyzers not suitable for high-volume testing.
Innovation Solution
A test system using an RF probe, reflectometer, and test measurement system that applies RF test signals to an intermediate node on the PCB, measures reflection coefficients, and converts them into impedance vectors for pass/fail determination, incorporating a calibration process to account for measurement errors using modified PCBs with known loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If radiated testing is used to test RF PCB, then the testing can be performed with simple equipment, but the measurement is not repeatable and not sensitive to matching circuit issues
Solution Approach 1:
The patent introduces an intermediary testing method using a reflectometer and RF probe to measure reflection coefficients at an intermediate node on the PCB. This mediator approach allows indirect measurement of matching circuit performance without requiring complex radiated testing setups, thereby improving measurement repeatability while keeping equipment relatively simple.
Solution Approach 2:
The patent replaces the mechanical/radiated testing approach with an electrical measurement approach using a reflectometer. Instead of relying on radiated RF signals that are sensitive to environmental factors, the system uses electrical reflection coefficient measurements at an intermediate node, substituting a more stable and repeatable measurement method.
2Measurement precision
If network analyzer is used for testing RF PCB, then accurate impedance measurement can be achieved, but the equipment is too expensive for mass production testing
Solution Approach 1:
The patent employs a reflectometer, which is a much cheaper alternative to a network analyzer, for mass production testing. The system uses disposable or low-cost test probes and fixtures that can be quickly replaced or recalibrated, providing adequate measurement precision without the high cost of network analyzers.
Solution Approach 2:
The patent changes the measurement parameters from full network analysis to reflection coefficient measurement only. By focusing on specific parameters (reflection coefficient at a single frequency or narrow bandwidth) rather than comprehensive S-parameter analysis, the system achieves sufficient impedance measurement accuracy with less expensive equipment suitable for mass production.
3Ease of operation
If conventional radiated testing is used, then the testing process is simple to set up, but it cannot accurately detect antenna issues or matching circuit problems
Solution Approach 1:
The patent introduces an intermediate measurement point on the PCB where the reflectometer probe connects. This intermediary location allows direct electrical measurement of the matching circuit's effect on the RF signal before it reaches the antenna, enabling reliable detection of matching circuit defects while maintaining relatively simple test setup procedures.
Solution Approach 2:
The patent extracts the measurement function from the final antenna output and places it at an intermediate node. By taking out the measurement point from the radiated field and placing it in the electrical domain at an intermediate location, the system can reliably detect matching circuit issues without requiring complex antenna radiation pattern measurements.
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 method provides a cost-effective and repeatable means to test RF PCBs by accurately determining impedance and identifying issues with matching circuits and antennas, suitable for mass production without the need for expensive network analyzers.
Implementation Method 1
detects a reflected RF signal from the RF probe
Data Source
AI summary
A test system for testing RF PCBs including an RF probe for interfacing an intermediate node of each RF PCB, an RF source providing an RF test signal, a reflectometer, and a test measurement system that makes a pass/fail determination of each RF PCB using a measured reflection coefficient. Each RF PCB includes an IC matching circuit and an antenna matching circuit coupled between an RFIC and an antenna, in which the intermediate RF node is between the matching circuits. The reflectometer outputs a measured reflection coefficient indicative of a comparison between a reflected RF signal and the RF test signal. The measured reflection coefficient may be corrected using error values based on a calibration procedure using a calibration kit with modified RF PCBs with known loads. The modified RF PCBs are measured with a network analyzer and the test system to calculate the error values used for production testing.