Magnetic Sensor Bridge Circuit for Uniform-Field Inspection

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Solution Overview

Problem

Magnetic sensors with circuits lacking sensitivity to uniform external magnetic fields cannot be inspected using a uniform magnetic field, hindering the manufacturing of magnetic encoders with high yield.

Innovation Solution

A magnetic sensor device with a bridge circuit comprising arms made of magnetic detection elements, where the resistance changes with the strength of a specific magnetic field component, but not with a uniform external magnetic field. This design includes a sub-pad connected between the ends of one arm and the die pad, allowing inspection with a uniform magnetic field.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a magnetic sensor includes a bridge circuit with magnetoresistive elements magnetized in opposite directions connected in series, then the circuit has no sensitivity to uniform external magnetic fields, but this prevents inspection of the magnetic sensor using a uniform magnetic field

Engineering Contradiction:

Improveinsensitivity to uniform external magnetic fieldVSAvoidinspectability of magnetic sensor

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The bridge circuit is segmented into multiple arms with magnetoresistive elements having different magnetization directions. By dividing the circuit this way, some arms respond to uniform magnetic fields while others compensate, allowing both insensitivity to uniform fields and sensitivity to position-dependent fields.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the magnetic sensor have different sensitivities to uniform magnetic fields. The first and second magnetoresistive elements in series have opposite magnetization directions, creating local differences in response to uniform fields while maintaining overall insensitivity.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If magnetoresistive elements are arranged in a direction orthogonal to the relative movement direction, then the magnetic sensor can detect position changes, but the circuit configuration reduces sensitivity to uniform external magnetic fields

Engineering Contradiction:

Improveposition detection capabilityVSAvoidsensitivity to uniform external magnetic field

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The bridge circuit uses asymmetric magnetization directions for different magnetoresistive elements. While the overall structure maintains symmetry for position detection, the internal magnetization arrangement creates asymmetric responses to uniform magnetic fields, enabling both functions.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

Instead of making the entire sensor sensitive to uniform fields for inspection, the invention makes specific parts (individual magnetoresistive elements) sensitive while others compensate, inverting the conventional approach of making the whole sensor uniformly sensitive.

Inventive Principle:

Principle #13The other way round (Inversion)

3Productivity

If a uniform magnetic field is applied for inspection before assembly, then manufacturing yield can be improved, but the circuit configuration causes the resistance and output to remain unchanged

Engineering Contradiction:

Improvemanufacturing yieldVSAvoidoutput change detectability

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The bridge circuit acts as an intermediary that converts uniform magnetic field effects into measurable resistance changes in specific arms, while maintaining overall insensitivity. This allows inspection through the intermediary response of individual arms.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the parameter configuration by using multiple magnetoresistive elements with different magnetization directions in series, creating a circuit where uniform magnetic fields produce measurable changes in specific arms while maintaining overall stability.

Inventive Principle:

Principle #35Parameter changes

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

Enables the inspection of magnetic sensors using a uniform external magnetic field, ensuring the quality of magnetic encoders and improving manufacturing yield.

Implementation Method 1

a plurality of arms being each constituted of a plurality of magnetic detection elements and configured such that a resistance changes according to change of strength of the magnetic field component

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Implementation Method 2

the magnetic sensor detects the strength of the component of the target magnetic field in one direction, and generates two detection signals that correspond to the strength of the component in the one direction and have respective different phases

Methodology Applied

Scientific EffectMagnetic field detection: Magnetic Field

Data Source

PatentUS12345783B2Magnetic sensor device and magnetic encoder

Publication Date: 2025.07.01 TDK CORP

AI summary

A magnetic sensor device includes a magnetic sensor, a die pad, and four leads. The magnetic sensor includes a bridge circuit including a plurality of arms and a plurality of pads electrically connected to the bridge circuit. One of the plurality of arms is provided between one of the plurality of pads and a different one of the plurality of pads in circuit configuration. The magnetic sensor further includes a sub-pad electrically connected between one end and another end of the one arm and also electrically connected to the die pad.