MR Bridge Circuit Switching for Electrical Offset Compensation
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Solution Overview
Problem
Magnetic field sensors with magnetoresistance (MR) bridges face challenges in accurately measuring magnetic fields due to electrical offset components caused by mismatches between MR elements, which cannot be compensated using current spinning methods like those in Hall plates, leading to inaccurate readings even in the absence of applied magnetic fields.
Innovation Solution
The implementation of a bridge circuitry with additional switches and offset processing circuitry that measures output voltages in different modes to isolate and remove electrical offset components, allowing for accurate magnetic field sensing by switching between modes faster than the maximum signal frequency and offset drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a standard Wheatstone bridge with four MR elements is used, then the device complexity is low, but measurement precision deteriorates due to electrical offset components from element mismatches
Solution Approach 1:
The bridge is divided into two separate half-bridges (first half-bridge with MR elements 302a-304a, second half-bridge with MR elements 302b-304b), each measuring different magnetic field components. This segmentation allows independent offset compensation for each half-bridge while maintaining overall measurement accuracy.
Solution Approach 2:
The circuit periodically switches between different measurement modes (first mode measuring along first axis, second mode measuring along second axis) using switches 312-319 controlled by clock signals. This periodic switching enables temporal separation of offset measurement and signal measurement, allowing offset compensation without continuous complex circuitry.
2Measurement precision
If current spinning methods are used for offset compensation, then the ease of operation is improved, but measurement precision deteriorates because these methods cannot compensate electrical offset in MR bridges
Solution Approach 1:
The circuit performs preliminary offset measurement by switching to a mode where only offset voltages are present (without magnetic field signal) and stores this offset information. This preliminary action allows the offset to be measured and compensated before the actual magnetic field measurement, separating offset effects from signal effects.
Solution Approach 2:
Additional MR elements (302a, 302b, 304a, 304b) are introduced as intermediary components that, combined with the switching network, enable the separation and independent measurement of offset components from magnetic field signal components. These intermediary elements facilitate the offset compensation function.
3Measurement precision
If additional MR elements and switches are added to the bridge, then measurement precision is improved through offset compensation, but device complexity increases
Solution Approach 1:
The additional MR elements and switches serve multiple functions: they enable offset measurement, facilitate mode switching between different measurement axes, and maintain bridge balance. This multi-functionality justifies the increased component count by providing several critical functions within the same added components.
Solution Approach 2:
The bridge circuitry is made dynamic through the switching network (switches 312-319) that can reconfigure the circuit topology based on the measurement mode. This dynamic reconfiguration allows the same hardware to perform different measurement functions, reducing the need for entirely separate circuits for offset compensation and signal measurement.
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 significantly improves the accuracy of MR bridges by effectively compensating for electrical offset and drift, ensuring precise magnetic field measurements by eliminating error components from the output voltage.
Implementation Method 1
MR elements have an electrical resistance that changes in the presence of an external magnetic field
Implementation Method 2
measures output voltages in different modes to isolate and remove electrical offset components
Data Source
AI summary
In one aspect, bridge circuitry includes a first magnetoresistance (MR) element connected with a second MR element at a first node; a third MR element connected with the first MR element at a second node; a fourth MR element connected with the third MR element at a third node; a fifth MR element connected with a sixth MR element at a fourth node; a seventh MR element connected with the fifth MR element at a fifth node; and an eighth MR element connected with the seventh MR element at a sixth node; and a plurality of eight switches. Six of the plurality of eight switches are each connected to a corresponding one node.