Magnetoresistance Bridge Sensor AC Mixing for Temperature Stability
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Solution Overview
Problem
Magnetoresistance elements in magnetic field sensors, such as GMR and TMR, face challenges with temperature variability and output signal stability due to mismatched temperature coefficients between fixed resistors and magnetoresistance elements, leading to inconsistent performance in half and full bridge configurations.
Innovation Solution
A magnetic field sensor design incorporating four magnetoresistance elements arranged in a bridge configuration with AC mixing currents and magnetic fields, generating a bridge output signal that is less temperature-dependent, using AC mixing currents and magnetic fields with different frequencies to produce a DC component responsive to external magnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fixed resistors are used in bridge configurations with magnetoresistance elements, then the bridge can be constructed, but the output signal varies with temperature due to mismatched temperature coefficients
Solution Approach 1:
The patent replaces fixed resistors with magnetoresistance elements in the bridge configuration, changing the component parameters to have matched temperature coefficients. This substitution transforms the temperature stability issue by ensuring all bridge elements exhibit similar temperature-dependent resistance characteristics, thereby eliminating the mismatch problem that caused output signal variation.
2Measurement precision
If magnetoresistance elements are used to achieve high sensitivity, then sensitivity is improved, but the operating range is restricted compared to Hall elements
Solution Approach 1:
The patent applies AC mixing currents with different frequencies to the magnetoresistance elements, creating periodic modulation of the resistance. This periodic action enables the extraction of DC output signals that are proportional to the applied magnetic field, effectively extending the linear operating range while preserving the high sensitivity characteristics of magnetoresistance elements.
3Reliability
If AC mixing currents with different frequencies are applied to magnetoresistance elements, then temperature stability is improved, but the device complexity increases
Solution Approach 1:
The patent introduces AC mixing currents as intermediary signals that modulate the resistance of magnetoresistance elements. These intermediary AC signals serve as a mediator between the applied magnetic field and the output DC signal, enabling temperature-stable measurements while the frequency domain separation simplifies the extraction of useful information through standard filtering techniques.
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 stabilizes the output signal of magnetic field sensors, reducing temperature variability and enhancing sensitivity and linearity across a broader range of magnetic fields, while maintaining robustness against temperature fluctuations.
Implementation Method 1
The magnetoresistance element has a resistance that changes in relation to a magnetic field experienced by the magnetoresistance element
Implementation Method 2
at least one current generating circuit operable to generate first and second AC mixing currents... at least one magnetic field generating circuit operable to generate first, second, third, and fourth AC mixing magnetic fields
Data Source
Figure 1
Figure 2~3
Figure 3A
AI summary
A magnetic field sensor and an associated method use one or more magnetoresistance elements ( 1302, 1304, 1306, 1308) driven with an AC mixing current (1312, 1316) and experiencing an AC mixing magnetic field which have AC components of the same frequency (fmod), such as to generate a DC voltage signal (1334a, 1334b) or a DC voltage signal component related to a slope of a transfer curve of the one or more magnetoresistance elements, wherein the mixing takes place in the magnetoresistance element(s) and results in changes of the value of the DC component in response to changes of the sensed external magnetic field.