Single Ended Test Probe Ground Arm Rotation
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Solution Overview
Problem
Establishing a temporary electrical connection between a 50 Ohm coaxial cable and test points on a device under test (DUT) is challenging due to high inductance, which affects bandwidth and common mode rejection, making it difficult to achieve a satisfactory connection without introducing unwanted input signals.
Innovation Solution
A single-ended test probe design featuring a coaxial cable with a signal conductor and a rotatable ground arm connected via an electrically conductive ground member, which minimizes inductance and allows for adjustable span between signal and ground tips, enabling effective contact with DUT points while maintaining high bandwidth and common mode rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coaxial cable is used to establish temporary electrical connection to test points, then the connection is established, but high inductance is introduced which affects bandwidth and common mode rejection
Solution Approach 1:
The ground connection is segmented into two separate points along the coaxial cable shield rather than using a single ground tip. This segmentation creates two ground contact points that are spatially distributed, allowing the ground arm to rotate and adjust while maintaining low inductance through the distributed grounding approach
Solution Approach 2:
The ground connection is extended from a single-point contact in three-dimensional space to a distributed multi-point contact along the cable length. By projecting the ground member at an offset location and creating a second ground contact point, the solution transforms the ground path from a simple linear connection to a distributed spatial arrangement that reduces inductance
2Length of moving object
If the ground tip is positioned close to the signal tip, then the span is reduced for compact testing, but the ability to accommodate various DUT configurations is limited
Solution Approach 1:
The ground arm is made rotatable relative to the probe body, transforming the fixed span into a dynamic, adjustable span. This allows the user to rotate the ground arm to different angular positions, thereby changing the effective span between signal and ground tips to match various DUT configurations while maintaining a compact overall probe structure
Solution Approach 2:
The rotatable ground arm mechanism provides universal adaptability to accommodate multiple DUT configurations (ground-signal, ground-signal-ground, and other arrangements) with a single probe design. The ability to adjust the span and orientation makes the probe versatile for different testing scenarios without requiring multiple specialized probes
Data Source
AI summary
A single-ended test probe includes a probe body such as a coaxial cable, a signal tip integral with the core (signal conductor), to ground arm having a ground tip and mounted to the coaxial cable, and an electrically conductive ground member projecting outside the coaxial cable and electrically conductively connecting the ground arm to the shield (ground conductor) of the coaxial cable. The ground member may be located closer to the end of the cable than the location at which the ground arm is mounted to the cable to minimize inductance in the connection between the probe and a device under test. The ground member may also be a cam by which the span between the ground and signal tips can be adjusted. Also, the test probe may include a second ground arm that is detachable connectable to the probe body independently of the first.