Magnetic Field Detection Apparatus Offset Voltage Elimination
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Solution Overview
Problem
Magnetic field detection apparatuses using magneto-resistive elements face challenges in accurately measuring the direction of magnetic fields due to offset voltages generated by property deviations and temperature changes, leading to measurement errors and increased production and inspection complexities.
Innovation Solution
A magnetic field detection apparatus is designed with a configuration of four magneto-resistive elements connected in a specific manner, allowing for the elimination of offset voltages by adjusting the excitation voltages applied to half-bridge circuits, ensuring accurate measurements regardless of temperature changes without requiring temperature measurement means.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Wheatstone bridge configuration with four magneto-resistive elements is used, then magnetic field detection is enabled, but offset voltages are generated due to property deviations leading to measurement errors
Solution Approach 1:
The Wheatstone bridge is divided into two independent half-bridges, each driven by separate excitation voltage sources. This segmentation allows independent adjustment of excitation voltages to compensate for property deviations in magneto-resistive elements, eliminating offset voltages and improving measurement accuracy without compromising reliability
Solution Approach 2:
The invention changes the excitation voltage parameters (applying different voltages to the two half-bridges) to compensate for property deviations in the magneto-resistive elements. By adjusting these electrical parameters, offset voltages are eliminated while maintaining measurement precision and reliability
2Measurement precision
If conventional Wheatstone bridge configuration is used, then magnetic field detection is enabled, but temperature changes cause property deviations leading to offset voltages and measurement errors
Solution Approach 1:
Dividing the bridge into two independently excited half-bridges allows each half to be compensated for temperature-induced property deviations. The separate excitation voltage sources enable independent adjustment to maintain measurement precision across varying temperatures without requiring temperature measurement means
Solution Approach 2:
By changing the excitation voltage parameters applied to each half-bridge, the system compensates for temperature-induced property deviations in the magneto-resistive elements. This parameter adjustment eliminates temperature-related offset voltages while maintaining measurement accuracy
3Measurement precision
If conventional Wheatstone bridge configuration is used, then magnetic field detection is enabled, but production and inspection processes become complex due to offset voltage compensation requirements
Solution Approach 1:
The segmented half-bridge configuration with independent excitation sources simplifies production and inspection by eliminating the need for complex offset voltage compensation procedures. Each half-bridge can be independently calibrated, reducing overall system complexity while maintaining 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
This configuration enables accurate measurement of magnetic field directions with reduced production and inspection complexities, as offset voltages are eliminated, and temperature stability is maintained across a wide range, enhancing the reliability and efficiency of the apparatus.
Implementation Method 1
A GMR element has a first magnetic layer (a pinned magnetic layer), a second magnetic layer (a free magnetic layer), and a non-magnetic layer (a spacer layer) sandwiched between the two magnetic layers. When an external magnetic field is applied to the GMR element, the magnetization direction of the pinned magnetic layer does not change and remains pinned, whereas the magnetization direction of the free magnetic layer changes in accordance with the direction of the external magnetic field. The magnitude of the resistance of the element changes depending on the difference Δθ between the magnetization direction θp of the pinned magnetic layer and the magnetization direction θf of the free magnetic layer
Implementation Method 2
A magnetization direction in a thin-film magnetic film is related to the spin direction of electrons in a magnetic material. Thus, when Δθ=0, the free magnetic layer and the pinned magnetic layer have a high percentage of electrons that spin in the same direction. Conversely, when Δθ=180°, the two magnetic layers have a high percentage of electrons that spin in opposite directions. When θ=0 as shown in FIG. 3A, electrons spinning to the right, which have escaped from the pinned magnetic layer 13, are not scattered in the free magnetic layer 11 almost at all. Meanwhile, when Δθ=180° as shown in FIG. 3B, electrons spinning to the right, which have escaped from the pinned magnetic layer 13, are scattered frequently upon entering the free magnetic layer 11
Data Source
AI summary
There has been a problem that a bridge circuit using magneto-resistive elements or transducer elements could output a signal including an offset voltage, which could result in lower measurement accuracy. In order to solve such a problem, half-bridges each having magneto-resistive elements or transducer elements are excited with different excitation voltages so that the offset voltage is eliminated and the measurement accuracy is improved.