Magnetic Field Sensor Bridge Configuration for Common Mode Rejection
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Solution Overview
Problem
Magnetic field sensors with back-bias arrangements face challenges in immunity to common mode fields and accurately sensing the movement of ferromagnetic targets, particularly in varying orientations and distances from the magnet.
Innovation Solution
A magnetic field sensor design featuring a bridge configuration with magnetoresistive sensing elements, positioned at specific orientations to detect both the flux deflection and divergence of magnetic fields, utilizing a substrate, magnet, and circuitry for signal processing to generate sinusoidal signals with minimal deformation, incorporating a spacer to maintain optimal distance and reduce harmonic errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a back-bias magnet is added to enhance sensing capability, then the sensor can detect magnetic fields from ferromagnetic targets, but the sensor becomes susceptible to common mode fields and noise
Solution Approach 1:
The sensor divides the sensing function into multiple independent sensing elements arranged in a bridge configuration. Each element responds to magnetic fields, but the differential bridge structure segments the measurement process to isolate the target signal from common mode fields, allowing precise detection while rejecting noise.
Solution Approach 2:
The sensing elements are positioned at specific locations around the back-bias magnet where the magnetic field gradient is optimal. This local positioning ensures that each element experiences a unique magnetic field environment, enabling the bridge circuit to differentiate between target-induced field variations and uniform common mode fields.
2Measurement precision
If the sensor is positioned closer to the target for better signal strength, then detection sensitivity improves, but angular error and signal deformation increase
Solution Approach 1:
The sensing elements are positioned asymmetrically relative to the back-bias magnet and target, with different spacing and orientations. This asymmetric arrangement creates distinct magnetic field experience for each element, allowing the bridge circuit to generate sinusoidal signals with reduced angular error and minimal signal deformation even at close distances.
3Measurement precision
If multiple sensing elements are used to improve measurement accuracy, then common mode rejection improves, but device complexity increases
Solution Approach 1:
Multiple sensing elements are merged into a single bridge configuration where their outputs are combined through differential measurement. This merging approach achieves common mode rejection and improved measurement accuracy while maintaining a compact, integrated structure that does not significantly increase overall device complexity.
4Area of stationary object
If the sensing elements are spaced closer together to reduce sensor size, then device compactness improves, but signal differentiation capability deteriorates
Solution Approach 1:
The sensing elements are arranged in multiple dimensions around the back-bias magnet, not just in a single linear array. This multi-dimensional positioning allows the elements to be spaced closely in terms of overall sensor footprint while maintaining sufficient separation in specific spatial relationships to the magnet poles, preserving signal differentiation capability within a compact form factor.
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 design provides enhanced immunity to common mode fields and accurate detection of target movement with reduced angular error and signal deformation, ensuring robust and precise sensing across varying orientations and distances.
Implementation Method 1
magnetoresistive sensing elements configured to generate a magnetic field signal indicative of movement of a target
Implementation Method 2
a magnet configured to generate a magnetic field and having a first surface adjacent to the object and a second surface distal from the object
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Methods and apparatus for a magnetic field sensor for measuring movement of a target including a substrate and a magnet. A first bridge structure has first and second pluralities of magnetic field sensing elements spaced from each other. An axis of sensitivity of the magnetic field sensing elements is rotated at a predetermined angle with respect to an axis of rotation of the target to generate an output signal corresponding to the position of the target and a change in a property of the magnetic field generated by the magnet.