XMR Full Bridge Sensor Shape Anisotropy Thermal Drift
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Solution Overview
Problem
Magnetic field sensors used in applications like wheel speed detection face challenges with thermal drift and signal jitter due to pitch mismatch and complex magnetization processes, especially when using GMR or TMR technology.
Innovation Solution
A magnetic field sensor design utilizing four XMR elements connected in a full bridge circuit with two diagonal elements having the same shape anisotropy and others with different shape anisotropies, allowing for robust signal detection with reduced thermal drift and improved signal amplitude, while maintaining manufacturing simplicity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GMR or TMR elements are used for magnetic field sensing, then sensitivity and signal amplitude are improved, but thermal drift and signal jitter increase due to pitch mismatch and complex magnetization processes
Solution Approach 1:
The sensor divides the magnetic field detection function into four separate XMR elements arranged in a full bridge circuit, with each element having different shape anisotropy. This segmentation allows independent optimization of each element's response characteristics to different magnetic field components, improving overall measurement precision while reducing thermal drift through differential measurement.
Solution Approach 2:
Each XMR element in the full bridge circuit is designed with different shape anisotropy tailored to its specific position and function. The first and fourth elements share one shape anisotropy configuration, while the second and third elements share another, creating local optimization that enhances signal amplitude and reduces pitch mismatch effects.
2Measurement precision
If XMR elements with different shape anisotropies are used in the full bridge circuit, then signal amplitude is improved and pitch mismatch is reduced, but device complexity increases
Solution Approach 1:
The full bridge circuit deliberately employs asymmetric shape anisotropy configurations among the four XMR elements. The first and fourth elements have one shape anisotropy configuration while the second and third elements have another, creating an asymmetric arrangement that optimizes the differential measurement of magnetic field components and enhances signal amplitude.
Solution Approach 2:
The full bridge circuit configuration serves multiple functions simultaneously: it provides differential measurement of magnetic field components, compensates for thermal drift through balanced bridge operation, reduces pitch mismatch effects, and enables independent ASIC design. This multi-functionality justifies the increased device complexity by delivering comprehensive performance improvements.
3Reliability
If a full bridge circuit with four XMR elements is implemented, then thermal drift is reduced and signal stability is improved, but manufacturing complexity increases
Solution Approach 1:
The full bridge circuit is designed to maintain equipotential relationships among corresponding nodes during operation, creating a balanced configuration where thermal drift effects cancel out. The symmetric arrangement of XMR elements with complementary shape anisotropies ensures that temperature-induced resistance changes affect all elements equally, resulting in net cancellation of thermal drift in the differential output.
Solution Approach 2:
The invention changes the shape anisotropy parameter of XMR elements in a systematic pattern around the full bridge circuit. By carefully selecting and arranging different shape anisotropy values in the four elements, the circuit achieves thermal drift compensation while maintaining manufacturability through standardized element designs that can be produced using existing fabrication processes.
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 solution provides a robust and accurate magnetic field sensing capability with reduced thermal drift and signal jitter, maintaining large signal amplitude and allowing for independent ASIC design, effectively addressing the limitations of existing GMR and TMR technologies.
Implementation Method 1
The at least four XMR elements are GMR or TMR elements (GMR=giant magnetoresistance; TMR=tunnel magnetoresistance)
Implementation Method 2
The at least four XMR elements are GMR or TMR elements (GMR=giant magnetoresistance; TMR=tunnel magnetoresistance)
Implementation Method 3
Two diagonal XMR elements of the full bridge circuit comprise the same shape anisotropy, wherein XMR elements in the same branch of the full bridge circuit comprise different shape anisotropies
Data Source
AI summary
Embodiments of the present invention provide a magnetic field sensor. The magnetic field sensor includes at least four XMR elements connected in a full bridge circuit including parallel branches. The at least four XMR elements are GMR or TMR elements (GMR=giant magnetoresistance; TMR=tunnel magnetoresistance). Two diagonal XMR elements of the full bridge circuit include the same shape anisotropy, wherein XMR elements in the same branch of the full bridge circuit include different shape anisotropies.