Magnetic Field Sensor Switching Circuit for Stray Field Rejection
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Solution Overview
Problem
Magnetic field sensors often suffer from undesirable DC offset voltage and stray magnetic field effects, which conventional methods struggle to effectively cancel, leading to inefficiencies and increased complexity in signal processing.
Innovation Solution
A magnetic field sensor design employing two spatially separated magnetic field sensing elements, where the output signals from these elements are combined with inverted polarities to cancel stray field effects, using a switching and amplification circuit that generates a combined signal with reduced DC offset and stray field immunity, potentially utilizing a single amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spatially separated magnetic field sensing elements are used to reduce stray magnetic field effects, then stray field immunity is improved, but device complexity increases due to multiple sensing elements and signal processing requirements
Solution Approach 1:
The patent combines multiple sensing elements (first and second magnetic field sensing elements) into a unified sensor structure where their outputs are processed together. The differential configuration merges the sensing functions while the shared amplifier and processing circuitry consolidate the overall device complexity, achieving stray field rejection without proportionally increasing system complexity.
2Reliability
If differential magnetic field sensing elements are used to generate differential signals, then stray magnetic field effects are reduced, but DC offset voltage problems persist in Hall effect elements
Solution Approach 1:
The patent converts the harmful DC offset voltage into a benefit by using it as a reference signal. The circuit measures the DC offset component separately and subtracts it from the total signal, thereby eliminating its harmful effect. This approach transforms the DC offset from an error source into a useful reference for calibration and compensation.
Solution Approach 2:
The patent segments the magnetic field sensing function into distinct components: the first and second sensing elements for differential measurement, and a separate processing path for DC offset compensation. By dividing the signal processing into distinct stages (differential amplification, DC offset measurement, and compensation), the system addresses both stray field rejection and DC offset elimination independently and effectively.
3Productivity
If complex ADC and DSP circuits are used to process magnetic field signals, then signal processing capability is improved, but cost and power consumption increase
Solution Approach 1:
The patent replaces complex digital signal processing (DSP) and analog-to-digital conversion (ADC) circuits with a simpler analog-based differential amplification and DC offset compensation system. By performing signal processing in the analog domain using operational amplifiers and resistor networks, the design eliminates the need for power-hungry ADC and DSP components while maintaining effective stray field rejection and DC offset elimination.
Solution Approach 2:
The patent employs simple, low-cost analog components (operational amplifiers, resistors, capacitors) instead of expensive and power-intensive digital processing circuits. The differential amplifier configuration and DC offset compensation use basic analog building blocks that are inexpensive, low-power, and sufficient for the application requirements, thereby reducing both cost and power consumption.
4Measurement precision
If multiple amplifiers are used to process signals from multiple sensing elements, then signal processing accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the amplification function into a single differential amplifier that simultaneously processes signals from both the first and second magnetic field sensing elements. This single amplifier configuration provides the necessary signal conditioning and rejection of common-mode signals (including stray fields) without requiring multiple separate amplifiers, thereby reducing device complexity and component count while maintaining measurement precision.
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 solution achieves improved stray field immunity, reduces DC offset, and simplifies signal processing by eliminating the need for complex ADC and DSP, resulting in lower cost, lower power consumption, and a smaller physical footprint.
Implementation Method 1
Various magnetic field sensors may employ a variety of types of magnetic field sensing elements, including, but not limited to, Hall effect elements, magnetoresistance elements, and magnetotransistors. Hall effect elements generate an output voltage proportional to a magnetic field.
Data Source
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AI summary
Described embodiments provide a magnetic field sensor that includes first and second spaced magnetic field sensing elements that each generate a signal indicative of a magnetic field associated with a target. A switching module couples a first terminal of the first magnetic field sensing element having a first polarity to a first terminal of the second magnetic field sensing element having a polarity opposite the first polarity to generate a first combined signal. The switching module couples a second terminal of the first magnetic field sensing element having a polarity opposite the first polarity to a second terminal of the second magnetic field sensing element having the first polarity to generate a second combined signal. The switching module simultaneously couples the first and the second combined signals to an amplifier, which generates an output signal indicative of the magnetic field that has stray magnetic field effects cancelled.