Low Inductance Test Fixture for RF Current Monitoring
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Solution Overview
Problem
In high-frequency RF circuits, traditional resistors with leads introduce distortion due to inductance, and while surface mount resistors minimize this, other components like metal tracks and wires still impact RF signals, necessitating a solution to minimize inductance in signal monitoring systems.
Innovation Solution
A test fixture with a baseplate and coaxial connector, where surface mount resistors are embedded in slots on the baseplate, minimizing inductive contributions by eliminating leads and optimizing current paths for low inductance and high bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If leaded resistors are used in RF circuits, then the resistor can provide current limiting and voltage drop functions, but the inherent inductance of the leads introduces distortion and disturbance into RF signals
Solution Approach 1:
The patent extracts and removes the leads from the resistor structure, transitioning from leaded to surface mount resistors. This extraction eliminates the primary source of inductance (the leads) while retaining the resistor's core functionality for current limiting and voltage drop in RF circuits.
Solution Approach 2:
The patent changes the physical configuration parameter of the resistor from leaded to surface mount type. This parameter change fundamentally alters the inductance characteristic, reducing it from typical leaded resistor values to significantly lower values suitable for high-frequency RF applications.
2Object-affected harmful factors
If surface mount resistors are used to minimize inductance, then inductive contribution is reduced, but other components like metal tracks, connecting wires, and component layout still adversely impact RF signals
Solution Approach 1:
The patent merges the resistor with the PCB structure by embedding surface mount resistors directly into the circuit board layout. This integration minimizes the length of connecting metal tracks and wires, thereby reducing their inductive contribution while maintaining electrical connectivity.
Solution Approach 2:
The patent transitions from traditional through-hole mounting (z-dimension focus) to surface mount technology (xy-plane optimization). This dimensional change allows for optimized PCB trace routing and component placement that minimizes loop area and inductance in the RF signal path.
3Ease of operation
If conventional test fixtures are used for observing RF signals, then the setup is simple and straightforward, but the inductance from leads and connecting paths distorts the RF signal being measured
Solution Approach 1:
The patent introduces a specialized test fixture structure that acts as an intermediary between the RF circuit under test and the measurement instrument. This fixture provides low-inductance connection paths and optimized grounding, serving as a mediator that preserves signal integrity while enabling straightforward measurements.
Solution Approach 2:
The patent implements equipotential grounding structures in the test fixture, ensuring that all ground connections are at the same potential. This eliminates ground loops and minimizes inductive coupling between signal and ground paths, thereby improving measurement accuracy without complicating the measurement process.
Data Source
AI summary
The illustrative embodiments pertain to a test fixture having low insertion inductance for large bandwidth monitoring of current signals. In one exemplary embodiment, the test fixture includes a baseplate with each resistor of a set of resistors embedded inside a respective non-plated through slot in the baseplate. A first terminal of each resistor is soldered to a top metallic zone of the baseplate and a second terminal soldered to a first of two bottom metallic zones of the baseplate. The top metallic zone is connected by plated-through holes to a second of the two bottom metallic zones. When mounted upon a PCB, the test fixture allows current flow from the first bottom metallic zone, upwards through the set of resistors to the top metallic zone, and downwards to the second bottom metallic zone. An observation instrument may be coupled to a coaxial connector that is mounted on the baseplate.