Magnetic Sensor Bridge Circuit Compensation Resistor
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Solution Overview
Problem
The use of tunnel magneto-resistance elements in magnetic sensors results in voltage-dependent resistance characteristics, causing the output waveform to deviate from a cosine or sine wave, which reduces the accuracy of magnetic field direction calculations.
Innovation Solution
Incorporating a compensation resistor in the bridge circuit with TMR elements, where the resistance varies with a period of 180 degrees relative to the external magnetic field, to stabilize the output waveform and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If tunnel magneto-resistance elements are used in the magnetic sensor, then the magneto resistance ratio is improved, but the output waveform deviates from a cosine or sine wave due to voltage-dependent resistance characteristics
Solution Approach 1:
A compensation resistor is introduced as an intermediary element in the bridge circuit. This compensation resistor has resistance characteristics that vary with the external magnetic field in a manner that compensates for the voltage-dependent resistance variations of the TMR elements, thereby restoring the output waveform to a proper cosine or sine wave shape
Solution Approach 2:
The invention changes the resistance parameter of the compensation resistor to vary with the external magnetic field. By designing the compensation resistor with specific magnetic field-dependent resistance characteristics, the overall bridge circuit output waveform is corrected to maintain accuracy while using TMR elements
2Power
If TMR elements are used in the bridge circuit, then the sensitivity is improved, but the resistance characteristics become voltage-dependent causing waveform distortion
Solution Approach 1:
The compensation resistor serves as a mediator that counteracts the voltage-dependent resistance effects of the TMR elements. By placing this compensation element in the bridge circuit, the sensitivity benefits of TMR are preserved while the waveform distortion is corrected
3Measurement precision
If the magnetization direction in the magnetization fixed layer is made opposite in second and fourth MR elements, then the bridge circuit output response to external magnetic field is improved, but the voltage dependence of TMR elements still causes waveform deviation
Solution Approach 1:
The compensation resistor is introduced as a corrective element that compensates for the waveform distortion caused by voltage-dependent TMR characteristics, while maintaining the beneficial opposite magnetization configuration in the bridge circuit
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 magnetic sensor achieves improved accuracy by ensuring the output waveform resembles a cosine wave, reducing detection errors and maintaining consistency with the expected waveform shape.
Implementation Method 1
An example of an MR element with a high MR ratio is a tunnel magneto-resistance element (TMR element) that utilizes a tunnel magneto-resistance effect
Implementation Method 2
Magneto resistance (MR) elements configured to exert magneto resistance effects are widely utilized as sensors for detecting a magnetic field because the electric resistance value of the MR elements vary in response to the external magnetic field
Data Source
AI summary
A magnetic sensor includes a bridge circuit with a first, a second, a third, and a fourth resistor annularly and electrically connected together in this order, and a compensation resistor. The compensation resistor is connected to a first point between the fourth resistor and the first resistor. The first to fourth resistors include a first to fourth tunnel magneto-resistance element, respectively. Each of the magnetization directions in the magnetization fixed layers in the second and fourth magneto resistance elements is opposite to the magnetization direction in the magnetization fixed layer in the first magneto resistance element. The magnetization direction in the magnetization fixed layer in the third magneto resistance element is the same as the magnetization direction in the magnetization fixed layer in the first magneto resistance element. The resistance of the compensation resistor varies with a period of 180 degrees with respect to a rotation angle of the external field.