Back-Biased Magnetic Field Sensor Differential Proximity Detection
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Solution Overview
Problem
Conventional back-biased proximity sensors using a single planar Hall effect element are limited in their ability to distinguish proximity of a ferromagnetic object due to non-responsive differential arrangements when using two planar Hall effect elements, which are equally affected by the object, resulting in no output.
Innovation Solution
A back-biased magnetic field sensor employing a differential arrangement with multiple vertical Hall effect elements or magnetoresistance elements, positioned outside a substrate region, which provides improved sensitivity and noise ratio by generating distinct signals in response to the proximity of a ferromagnetic object, thereby overcoming the limitations of single-ended configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single planar Hall effect element is used in a back-biased arrangement, then the sensor can detect ferromagnetic object proximity, but the sensor lacks differential capability to reject external magnetic field interference
Solution Approach 1:
The sensor is segmented into multiple planar Hall effect elements (first and second elements) arranged in a differential configuration. Each element independently senses magnetic field components, allowing the system to compute differences that reject common-mode external interference while preserving proximity detection capability.
Solution Approach 2:
Multiple planar Hall effect elements are merged into a unified differential sensing system where their outputs are combined through subtraction. This merging enables the sensor to simultaneously achieve external field rejection and proximity detection by processing the combined signals from all elements.
2Reliability
If two planar Hall effect elements are used in a differential arrangement, then external magnetic field rejection is improved, but both elements respond equally to proximate ferromagnetic objects resulting in zero output
Solution Approach 1:
The two planar Hall effect elements are positioned at different locations with different maximum response axes orientations. This local differentiation ensures that while both elements experience external magnetic fields similarly (enabling rejection), they respond differently to the proximity magnetic field gradient, producing a non-zero differential output.
Solution Approach 2:
The sensor employs asymmetric positioning and orientation of the planar Hall effect elements relative to the magnet and substrate. The first element has its maximum response axis intersecting the ferromagnetic object while the second element has a different orientation, creating asymmetric responses to proximity objects that generate detectable differential signals.
3Measurement precision
If vertical Hall effect elements or magnetoresistance elements are used instead of planar Hall effect elements, then sensitivity and signal-to-noise ratio are improved, but the sensor structure becomes more complex
Solution Approach 1:
The sensor design changes the orientation parameter of the Hall effect elements from planar to vertical configuration. This parameter change increases the sensitivity to the magnetic field geometry generated by the back-biased magnet and ferromagnetic object proximity, thereby improving the signal-to-noise ratio and measurement precision.
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
The use of multiple vertical Hall effect elements or magnetoresistance elements enhances the signal-to-noise ratio and allows for effective detection of ferromagnetic object proximity, reducing interference from external magnetic fields and improving sensitivity, enabling accurate proximity sensing.
Implementation Method 1
Magnetic field sensors generally include a magnetic field sensing element... typically a planar Hall effect element
Implementation Method 2
Various types of magnetic field sensing elements are known, including Hall Effect elements and magnetoresistance elements
Implementation Method 3
a magnetic field sensed by a magnetic field sensor is a magnetic field generated by the magnet
Implementation Method 4
In the presence of a ferromagnetic object, the magnetic field generated by the magnet and sensed by the magnetic field sensor varies
Data Source
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AI summary
A back-biased magnetic field sensor uses one or more magnetic field sensing elements upon a substrate, each outside of a substrate region in which magnetic field lines are near perpendicular to the substrate and outside of which magnetic field lines are not to the substrate. The back-biased magnetic field sensor can sense an approaching and/or a retreating ferromagnetic object.