Magnetoresistive Angular Sensor Offset Compensation
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Solution Overview
Problem
Magnetic angular sensors face challenges in accurately detecting zero-field crossings due to symmetrical transfer curves, leading to sensitivity issues and offset problems, which are exacerbated by environmental changes and limited operating temperature ranges of GMR sensors, making offset compensation complex and impractical.
Innovation Solution
A magnetoresistive angular sensor system that uses an external magnetic field generator to provide two modes: a dominant DC field for initial calibration and a smaller field for measurement, allowing for offset voltage compensation by combining sensor outputs from these modes, effectively canceling offset voltages and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a symmetrical transfer curve is used in the magnetic sensor, then the sensor structure is simple, but the sensitivity near zero-field crossings is poor
Solution Approach 1:
The patent introduces an asymmetric bias magnetic field to break the symmetry of the transfer curve. By applying a DC bias field through a coil, the operating point is shifted from the symmetric zero-crossing region to an asymmetric region with higher slope, thereby improving sensitivity without fundamentally changing the sensor structure
2Measurement precision
If offset compensation methods are implemented, then measurement accuracy is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent performs offset compensation during the manufacturing process by applying a known bias magnetic field and adjusting the sensor output to compensate for offsets. This preliminary action eliminates the need for complex runtime compensation systems, reducing device complexity while maintaining measurement accuracy
Solution Approach 2:
The patent changes the operating parameters by applying a DC bias magnetic field that shifts the transfer curve. This parameter change allows the sensor to operate in a region where offset effects are minimized, improving measurement accuracy without adding complex compensation hardware
3Measurement precision
If GMR sensor technology is used to achieve high sensitivity, then the sensitivity is improved, but the operating temperature range is limited
Solution Approach 1:
The patent introduces an AMR sensor layer as an intermediary between the GMR effect and the readout circuitry. The AMR layer has better temperature stability than GMR, while still providing magnetoresistive sensitivity. This intermediary layer allows the system to achieve high sensitivity through the GMR effect while maintaining a broader operating temperature range through the AMR layer's thermal stability
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 approach enhances the accuracy of angular orientation measurements by dominating the sensor's magnetic field with an external field, enabling effective offset compensation and extending the angular range of magnetoresistive sensors beyond the limitations of individual elements.
Implementation Method 1
Anisotropic magnetoresistive (AMR) and giant magnetoresistive (GMR) sensors are particular examples of sensor types based on the magnetoresistive effect
Implementation Method 2
control means for controlling the external magnetic field generator; wherein the control means is adapted to control the external magnetic field generator to provide a first mode in which a dc external magnetic field is provided
Data Source
AI summary
A magnetoresistive angular sensing method is disclosed. In a first mode, a first dc external magnetic field in a predetermined direction is applied to an angular sensor arrangement in which the external magnetic field dominates over a magnetic field generated by an input device an angular position of which is to be sensed. In a second mode, a second external magnetic field is applied to the angular sensor. Outputs of the angular sensor arrangement in the two modes are processed to determine an angular orientation of the input device with offset voltage compensation.