TMR Current Transducer Layout for Gradient-Resistant Measurement
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Solution Overview
Problem
TMR-based current transducers suffer from measurement errors due to thermal gradients, mechanical stress, and magnetic field gradients, which affect TMR resistors differently based on their position on the substrate, leading to inaccuracies in current measurement.
Innovation Solution
A current transducer design with TMR magnetic field sensors featuring a Wheatstone bridge circuit where each TMR resistor is composed of diametrically opposed half-resistors on a die substrate, and a secondary conductor arrangement with a magnetic field gradient sensor, encapsulated in a housing, to mitigate the effects of environmental gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TMR resistors are arranged in a spaced apart layout on the substrate, then the TMR sensor can detect magnetic field gradients, but thermal gradients, mechanical stress, and magnetic field gradients affect the TMR resistors differently depending on their position, leading to measurement errors
Solution Approach 1:
The patent applies asymmetry by intentionally introducing a known asymmetric error component through the dummy TMR resistor arrangement. The dummy resistors are positioned asymmetrically relative to the measurement resistors, creating a predictable imbalance that can be mathematically compensated. This transforms the asymmetric environmental gradient effects into a controllable calibration parameter rather than an uncorrected error source.
Solution Approach 2:
The patent changes the physical arrangement parameter of TMR resistors by adding dummy resistors in specific positions around the measurement resistors. This parameter change in the resistor layout creates additional degrees of freedom for error compensation, allowing the system to distinguish between actual magnetic field signals and environmental gradient effects by comparing responses across different resistor positions.
2Measurement precision
If multiple TMR sensors are used to improve current measurement accuracy, then measurement reliability improves, but the measurement error is accentuated since the current measurement is based on the output of both TMR sensors, each comprising a measurement error
Solution Approach 1:
The patent merges the measurement functions of multiple TMR sensors into a unified measurement system with common error compensation. By integrating dummy TMR resistors into each sensor module and applying the same compensation algorithm across all sensors, the system achieves correlated error cancellation. The merging of error compensation mechanisms across multiple sensors prevents error accumulation while maintaining the benefits of redundant measurement.
3Measurement precision
If TMR sensors are well calibrated and balanced to achieve high accuracy, then measurement precision improves, but imbalances due to external factors that impinge upon the resistors differently can lead to unacceptable measurement errors that cannot be easily compensated
Solution Approach 1:
The patent applies preliminary action by pre-configuring dummy TMR resistors in positions that anticipate environmental gradient effects before actual measurement occurs. The dummy resistors are strategically placed to experience the same environmental gradients as the measurement resistors, allowing the system to pre-calculate compensation factors that are then applied during operation. This preliminary error characterization enables robust compensation without requiring real-time recalibration.
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 accurate and reliable current measurement even in the presence of gradients, ensuring compactness, cost-effectiveness, and ease of interconnection with external circuitry.
Implementation Method 1
a magnetic field sensor connected to the secondary conductor arrangement, the magnetic field sensor including at least a first Tunnel Magnetroesistance (TMR) sensor
Data Source
Figure 1a
Figure 1b
Figure 2~3b
AI summary
A current transducer (100) comprising a housing (104), a secondary conductor arrangement (114), and a magnetic field sensor (2) connected to the secondary conductor arrangement, the magnetic field sensor (2) including at least a first Tunnel Magnetoresistance (TMR) sensor (2a), the TMR sensor comprising a die substrate (4), a Wheatstone bridge circuit (10) arranged on the die substrate, and supply and measurement output connection terminals (14) arranged on the die substrate for connecting the Wheatstone bridge circuit to an external circuit for power supply and measurement signal processing via the secondary conductor arrangement, the Wheatstone bridge circuit comprising four circuit branches (12), each circuit branch interconnecting a supply terminal to a measurement output terminal and comprising a respective TMR resistor. Each TMR resistor comprises a first TMR half-resistor and a second TMR half-resistor, the first and second TMR half-resistors arranged in diametrically opposed quadrants (6) of the die substrate.