TMR Sensor Linearity via Asymmetric Current Routing
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Solution Overview
Problem
Magnetic field sensors, particularly TMR sensors, suffer from cross-axis effects due to sensitivity to orthogonal magnetic fields, leading to measurement inaccuracies and reduced linearity, which existing compensation algorithms cannot fully address.
Innovation Solution
The implementation of a TMR field sensor with a Wheatstone bridge circuit comprising multiple TMR transducer legs arranged in an m×n matrix, where built-in current lines adjacent to the fixed ferromagnetic layer generate a reset magnetic field, compensating for cross-axis interference by routing current lines to ensure opposing magnetic responses from sense elements, thereby minimizing cross-axis interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TMR sensors are designed to sense magnetic fields in one desired sensitive axis, then sensitivity to the desired axis is improved, but sensitivity to orthogonal cross-axis magnetic fields increases causing measurement inaccuracies
Solution Approach 1:
The sensor is divided into multiple TMR transducer legs arranged in a Wheatstone bridge circuit, with each leg containing multiple active sense elements. This segmentation allows the sensor to process magnetic field information from different orientations separately and combine them to eliminate cross-axis interference while maintaining sensitivity to the desired axis.
Solution Approach 2:
Current lines are routed asymmetrically through the TMR transducer legs such that sense elements experience opposing magnetic responses to cross-axis fields. This asymmetric routing creates differential signals that cancel out cross-axis interference while preserving sensitivity to the primary sensing axis.
2Measurement precision
If magnetic sensor output processing algorithms are used to compensate for offset and uniform sensitivity mismatch, then offset compensation is improved, but field dependent sensitivity differences remain unaddressed
Solution Approach 1:
The Wheatstone bridge circuit and current line routing are designed in advance to pre-compensate for field dependent sensitivity differences. By structuring the sensor to inherently produce differential signals that cancel cross-axis effects, the system eliminates the need for complex post-processing algorithms to address field dependent sensitivity variations.
3Measurement precision
If cross-axis effects are reduced through sensor design, then measurement linearity is improved, but device complexity increases due to multiple transducer legs and current line routing
Solution Approach 1:
Multiple TMR transducer legs are merged into a single Wheatstone bridge circuit configuration, where the legs work together as an integrated unit. This merging allows cross-axis compensation to be achieved through the collective behavior of the legs rather than requiring complex individual leg designs, thereby reducing overall device complexity while maintaining measurement linearity.
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 configuration significantly enhances magnetic field measurement linearity and reduces cross-axis interference, improving the accuracy and reliability of magnetic field sensing across multiple axes.
Implementation Method 1
a reset current is applied to the built-in current lines. When the reset current is applied, a magnetic field is generated on the first ferromagnetic layer (e.g., the free layer)
Implementation Method 2
A magnetic field sensor based on TMR therefore converts magnetic field into electrical signal by a change in electrical resistance due to the changing angle of the magnetic free layer relative to the fixed layer in response to the field
Data Source
AI summary
A magnetic field sensor includes a plurality of transducer legs coupled together as a first circuit to sense a magnetic field, wherein each transducer leg comprises a plurality of magnetoresistance sense elements. The magnetic field sensor also includes a second circuit including a first plurality of current lines, wherein each current line of the first plurality of current lines is adjacent to a corresponding plurality of magnetoresistance sense elements of a transducer leg of the plurality of transducer legs. When at least one current line of the first plurality of current lines is energized, a magnetization of each magnetoresistance sense element of the transducer leg is aligned in a first direction or a second direction opposite to the first direction. A routing pattern of the at least one current line is configured to generate an equal population of magnetoresistance sense elements with magnetization aligned in the first and second directions.