AMR Sensor Offset Correction via Commutating Demodulator
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Solution Overview
Problem
Anisotropic magneto-resistive sensors face challenges in reducing bias offset and temperature sensitivity, leading to increased complexity, power consumption, and reduced bandwidth in existing offset correction methods, which often require additional processing and components.
Innovation Solution
The proposed solution involves using the equation Vmag = (Vo(set) - Vo(reset))/2 to directly calculate the magnetic field strength without microprocessor intervention, utilizing a commutating demodulator to produce differential signals that eliminate offset bias independently of temperature, thereby simplifying the measurement process and reducing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital subtraction scheme is used to remove offset, then offset bias is reduced, but dynamic range is lost and microprocessor is required
Solution Approach 1:
The patent extracts the offset voltage measurement from the main signal path by using a dedicated offset measurement mode. The system separates offset measurement (when no external field is present) from normal operation, allowing the offset to be measured and stored independently without affecting the main measurement chain or requiring complex processing.
Solution Approach 2:
The patent performs offset measurement and correction in advance before actual magnetic field measurements are taken. By measuring the offset voltage first (when Bexternal = 0) and storing it for later subtraction, the system eliminates the need for real-time microprocessor intervention during normal operation.
2Measurement precision
If offset current feedback is used, then offset bias is removed, but device complexity and manufacturing time increase
Solution Approach 1:
The patent implements a self-calibrating system that automatically measures and corrects its own offset voltage without requiring external adjustment or complex feedback circuitry. The microprocessor controls the measurement process and performs the subtraction automatically, making the system self-sufficient and easier to manufacture.
3Measurement precision
If integrator frequency is set far below toggle frequency, then offset is extracted, but circuit size increases and bandwidth is reduced
Solution Approach 1:
The patent replaces the analog integrator-based offset removal system with a digital subtraction approach. Instead of using an integrator circuit that requires careful frequency tuning and occupies physical space, the system uses digital processing to subtract the stored offset value from measurements, eliminating the need for complex analog filtering and preserving bandwidth.
4Speed
If clock frequency is increased to improve servo operation, then bandwidth is maintained, but power consumption increases and self-heating occurs
Solution Approach 1:
The patent uses periodic switching between measurement modes (normal measurement and offset measurement) controlled by the microprocessor. This periodic action allows offset to be measured at appropriate intervals without requiring continuous high-frequency operation, thereby reducing average power consumption and self-heating while maintaining measurement accuracy.
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 allows for accurate and efficient removal of offset bias without additional processing, reducing power consumption and manufacturing costs, while maintaining high bandwidth and resolution, making it suitable for applications like magnetic compassing and multi-axis detection systems.
Implementation Method 1
Anisotropic magneto-resistive (AMR) sensors are used in many devices from compasses to steering and positioning devices
Data Source
AI summary
Method and apparatus improve sensing accuracy and reduce bias shift in anisotropic magneto-resistive sensors using paired integrators and sampling switches for processing outputs of the sensor on applied set and reset signals with high immunity to temperature variations.