Magnetic Field Sensor DC Offset Compensation via Gain Circuit

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Solution Overview

Problem

Magnetic field sensors, particularly those using circular vertical Hall elements, face challenges with DC offsets and temperature effects, which impact accuracy and require bandpass filtering, limiting their precision and operational efficiency.

Innovation Solution

A magnetic field sensor system that includes a sequence switch circuit, a memory device for potentiometer control values, and a gain circuit to generate a clamped output signal, reducing DC offsets and eliminating the need for bandpass filtering while maintaining high accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a CVH sensing element with multiple vertical Hall elements is used to sense magnetic field direction, then the sensor can provide angle measurement capability, but each vertical Hall element introduces different DC offsets that degrade measurement accuracy

Engineering Contradiction:

Improveangle measurement capabilityVSAvoidDC offset accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent applies parameter changes by dynamically adjusting the gain of each vertical Hall element's output signal through individual gain circuits. By varying the gain parameter for each element, the system compensates for their different DC offsets and achieves uniform output characteristics, thereby maintaining angle measurement capability while improving DC offset accuracy.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If bandpass filtering is applied to reduce DC offsets and temperature effects, then measurement accuracy improves, but the device complexity increases and operational efficiency decreases

Engineering Contradiction:

ImproveaccuracyVSAvoidfiltering requirements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the need for bandpass filtering by implementing individual gain circuits for each vertical Hall element. These gain circuits directly compensate for DC offsets and temperature effects through precise gain adjustment, achieving the same accuracy improvement without requiring separate filtering stages, thus reducing device complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/filter-based approach (bandpass filtering) with an electronic control approach (individual gain circuits). Instead of using passive filtering components that increase device complexity, the system uses active electronic gain adjustment to achieve the same goal of reducing DC offsets and temperature effects, thereby improving operational efficiency.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If individual gain circuits are added to compensate for DC offsets, then measurement accuracy improves, but the device complexity increases

Engineering Contradiction:

ImproveDC offset compensationVSAvoidcircuit structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies universality by designing the gain circuits to serve multiple functions: they compensate for DC offsets, adjust for temperature effects, and normalize the output signals from different vertical Hall elements. This multi-functionality achieves accurate DC offset compensation without requiring separate dedicated circuits for each function, thereby limiting the increase in device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reduces DC offsets and temperature-related errors, enhancing the accuracy of angle and speed measurements without requiring bandpass filtering, thus improving the overall performance of magnetic field sensors.

Implementation Method 1

One type of current sensor uses a Hall Effect magnetic field sensing element in proximity to a current-carrying conductor. A vertical Hall element tends to be responsive to magnetic field parallel to a surface of a substrate on which the vertical Hall element is formed.

Methodology Applied

Scientific EffectHall Effect: Hall Effect

Data Source

PatentUS9638766B2Magnetic field sensor with improved accuracy resulting from a variable potentiometer and a gain circuit

Publication Date: 2017.05.02 ALLEGRO MICROSYSTEMS LLC

AI summary

A magnetic field sensor includes a plurality of magnetic field sensing elements, wherein the plurality of magnetic field sensing elements is configured to generate a plurality of magnetic field signals, each magnetic field sisal responsive to a magnetic field. The magnetic field sensor additionally includes a sequence switches circuit coupled to the plurality of magnetic field sensing elements. The sequence switches circuit is configured to sequentially select from among the plurality of magnetic field signals to generate a sequenced output signal representative of sequentially selected ones of the plurality of magnetic field signals. The magnetic field sensor also includes a variable potentiometer coupled to the sequence switches circuit. The magnetic field sensor additionally includes a gain circuit coupled to receive a signal representative of the offset attenuated sequenced output signal. A corresponding method is also provided.