Magnetic Sensing Bridge Resistance Tuning for CMRR Correction
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Solution Overview
Problem
Existing sensors face challenges in achieving high common mode rejection ratio (CMRR) and offset correction, which are critical for safety-critical applications like automobile control systems, due to variations in resistance and sensitivity of magnetic field sensing elements.
Innovation Solution
A magnetic field sensor system incorporating a sensing bridge with a magnetoresistance element and passive resistor unit cells, a switching matrix, and a matrix controller to dynamically adjust resistance by coupling or decoupling resistor unit cells based on counter signal updates, ensuring CMRR and offset correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a magnetic field sensor uses fixed resistance sensing elements, then the device structure is simple, but resistive imbalances cause poor common mode rejection ratio (CMRR)
Solution Approach 1:
The patent implements dynamic resistance adjustment by replacing fixed resistors with switchable resistor networks. The sensing element includes multiple resistor units that can be selectively connected or disconnected through switching matrices, allowing the total resistance to be dynamically adjusted to compensate for resistive imbalances and optimize CMRR performance.
Solution Approach 2:
The patent changes the resistance parameter of the sensing element by providing multiple resistor units with different resistance values. A switching matrix selectively connects these resistor units to achieve precise resistance tuning, enabling compensation for manufacturing variations and temperature drift to improve CMRR.
2Measurement precision
If the sensor uses multiple passive resistor unit cells with switching matrix, then resistive imbalances are corrected, but the device complexity increases
Solution Approach 1:
The patent segments the resistance control function into multiple independent resistor units that can be individually switched. Each resistor unit can be independently connected or disconnected through the switching matrix, allowing fine-grained adjustment of the total resistance to achieve precise control and compensate for small resistance variations.
Solution Approach 2:
The patent implements a feedback mechanism where the controller monitors the sensing element resistance and automatically adjusts the switching matrix configuration to maintain the desired resistance value. This closed-loop control compensates for resistance drift due to temperature or aging without requiring manual calibration.
3Measurement precision
If the sensor operates without dynamic resistance adjustment, then the operation is simple, but sensitivity mismatches reduce measurement accuracy
Solution Approach 1:
The patent enables the sensor to automatically compensate for sensitivity mismatches through self-calibration. The controller periodically adjusts the resistance of sensing elements using the switching matrix based on internal reference measurements, eliminating the need for external calibration equipment or manual intervention while maintaining high measurement accuracy.
4Manufacturing precision
If the sensor uses fixed sensing element resistance, then manufacturing is simpler, but resistive imbalances lead to offset errors
Solution Approach 1:
The patent incorporates preliminary resistance matching by providing multiple resistor units with predetermined standard values during manufacturing. The switching matrix is pre-configured to select combinations of these standard resistors to achieve the desired total resistance, reducing the need for post-manufacturing trimming or calibration while improving resistance matching consistency.
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 system effectively maintains consistent sensor performance by dynamically adjusting resistance to compensate for variations, enhancing CMRR and offset correction, thereby meeting stringent safety and reliability requirements.
Implementation Method 1
a first element of a first element type that is responsive to a magnetic field - The first element type can be a tunneling magnetoresistance element (TMR)
Data Source
AI summary
A sensing bridge includes a first element type that is responsive to a magnetic field and a second element type that is not responsive to the magnetic field. The first element type can be a magnetoresistance element such as a TMR and the second element type can be a passive resistor. A switching matrix under control of a matrix controller is configured to change a total resistance of the sensing element by coupling or decoupling one or more dots of the TMR and/or passive resistor unit cells of the passive resistor to the sensing element. Test signal generation circuitry is configured to generate a common mode test magnetic field with which the common mode rejection ratio (CMRR) of a sensing bridge can be evaluated and corrected.