Magnetic Field Sensor Digital Potentiometer DC Offset Compensation
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Solution Overview
Problem
Magnetic field sensors, particularly circular vertical Hall (CVH) sensing elements, face challenges with DC offsets and accuracy, which are exacerbated by temperature variations, affecting the reliability of angle and rotation speed measurements.
Innovation Solution
A magnetic field sensor system that includes a plurality of magnetic field sensing elements with a sequence switch circuit and a digital potentiometer, which sequentially selects and attenuates signals to reduce DC offsets and improve accuracy, using potentiometer control values stored in a memory device to adjust for error voltages and temperature effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a plurality of vertical Hall elements are used to sense magnetic field direction, then angle measurement capability is improved, but DC offset errors increase due to individual element variations
Solution Approach 1:
The patent implements feedback by measuring the DC offset of each vertical Hall element and using this information to generate compensating signals. The offset measurement circuit measures the output signal of each element, and the offset compensation circuit uses these measurements to create correction signals that are subtracted from the original signals, thereby eliminating the harmful DC offsets while preserving the angle measurement capability.
Solution Approach 2:
The patent introduces intermediary circuits between the vertical Hall elements and the final output. The offset measurement circuit and offset compensation circuit act as intermediaries that process the raw signals from the Hall elements, measuring and correcting their DC offsets before the signals are combined for angle calculation. This intermediary processing step isolates the harmful offsets from the useful measurement signals.
2Measurement precision
If offset compensation circuits are added to reduce DC offsets, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges the offset compensation function with the existing signal processing path of the magnetic field sensor. The offset measurement and compensation circuits are integrated into the same chip and share common signal paths and power supplies with the main sensing circuitry. This merging approach allows offset correction to be achieved without adding separate, independent compensation systems, thereby limiting the increase in device complexity.
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 significantly reduces DC offsets and enhances the accuracy of angle and rotation speed measurements by dynamically adjusting signal offsets, thereby improving the overall performance and reliability of the magnetic field sensor.
Implementation Method 1
A magnetic field sensor includes a circular vertical Hall (CVH) sensing element having a plurality of vertical Hall elements
Data Source
AI summary
A magnetic field sensor with a plurality of magnetic field sensing elements is presented. The magnetic field sensor includes a sequences switches circuit to sequentially select from among the plurality of magnetic field signals. The magnetic field sensor further includes a memory device to store a plurality of potentiometer control values. Also included is a variable potentiometer to attenuate an offset of each one of the plurality of magnetic field signals by using a respective plurality of offset attenuation factors responsive to one or more of the plurality of potentiometer control values. A corresponding method is also described.