TMR Sensor Set/Reset Straps for Offset Compensation
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Solution Overview
Problem
Anisotropic magneto-resistive (AMR) sensors face limitations in accuracy and range due to external magnetic fields and temperature variations, leading to sensor saturation and inaccuracy in closed-loop current sensing applications, particularly below 25 amps.
Innovation Solution
Incorporating set/reset straps on TMR devices, which use a current-carrying trace to create a magnetic field that flips and stabilizes the magnetic domains, allowing for precise null balance and offset compensation, effectively extending the sensor range and improving accuracy across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AMR sensors are used for current sensing, then the sensor can detect magnetic fields and measure current, but the sensor range is limited to 25 amps due to sensor saturation and accuracy suffers from external magnetic fields and temperature variations
Solution Approach 1:
The patent transitions from AMR material to TMR material, fundamentally changing the physical parameter of magnetic field sensitivity. TMR devices exhibit higher sensitivity and do not saturate at the same field strengths as AMR devices, enabling accurate measurement beyond 25 amps while maintaining precision through the tunneling magneto-resistive effect
Solution Approach 2:
The set strap applies a preliminary magnetic field to establish a known reference state (null point) before measurement begins. This preliminary action compensates for offset errors caused by temperature variations and external magnetic fields, ensuring accurate measurements across the extended range
2Ease of operation
If AMR sensors operate in external magnetic fields, then the sensor can function in practical applications, but external magnetic fields cause shifts in electrical response and offset drift particularly below saturation fields
Solution Approach 1:
The offset strap provides a feedback mechanism that continuously compensates for shifts in electrical response caused by external magnetic fields and temperature variations. By measuring the offset from the null point and applying compensation, the system maintains measurement precision despite changing environmental conditions
Solution Approach 2:
The set strap establishes a preliminary reference state that defines the null point before measurement. This preliminary action creates a stable baseline that compensates for external magnetic field effects, allowing the sensor to maintain functionality and precision in practical applications
3Temperature
If temperature variations occur in AMR sensors, then the sensor operates in real-world conditions, but temperature changes modify the electrical response and create offset drift
Solution Approach 1:
The offset strap acts as a temperature compensation mechanism that provides feedback to counteract offset drift caused by temperature variations. By continuously monitoring and compensating for temperature-induced offset changes, the system maintains electrical response stability across a wide operating temperature range
Solution Approach 2:
The transition to TMR material changes the temperature dependence characteristics of the sensor. TMR devices exhibit different thermal behavior compared to AMR devices, and when combined with offset compensation, this parameter change enables stable operation across broader temperature ranges
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 use of set/reset straps in TMR devices enhances the sensitivity and range of current sensors, enabling accurate measurements beyond the limitations of AMR sensors, with improved resistance changes and reduced temperature-related offset drift.
Implementation Method 1
a sensing device configured to change electrical resistance in response to a magnetic field. The sensing device exhibits a tunneling magneto-resistive effect (TMR)
Implementation Method 2
a first current carrying conductor positioned in proximity to the TMR sensing device, such that upon an application of a sufficient current, a magnetic field is generated
Implementation Method 3
the magnetic field is sufficiently strong and properly oriented so as to cause a magnetization of a soft magnetic layer of the TMR sensing device, thereby causing a change of the TMR sensing device from one bi-stable state to another bi-stable state
Data Source
AI summary
A sensing device exhibits a tunneling magneto-resistive (TMR) effect, and changes electrical resistance in response to a magnetic field. A first current carrying conductor is positioned in proximity to the TMR sensing device, such that upon an application of a sufficient current, a magnetic field is generated. The magnetic field is sufficiently strong and properly oriented so as to cause a magnetization of a soft magnetic layer of the TMR sensing device, thereby causing a change of the TMR sensing device from one bi-stable state to another bi-stable state.