Magnetic Sensor Self-Test Circuit for Accurate Speed and Direction
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Solution Overview
Problem
Magnetic field sensors face challenges in accurately detecting speed and direction due to non-uniform magnetic fields, particularly when back bias magnets are used, leading to increased costs from additional circuitry and reduced air gap usability.
Innovation Solution
An apparatus with test circuits to verify the accuracy of speed and direction detection, including a counter for edge detection, a ramp generator for frequency testing, and an analog-to-digital converter for signal conversion accuracy, along with an oscillator to provide an oscillating output and a comparator to ensure voltage levels are within predetermined ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If back bias magnets are used to generate magnetic field, then the magnetic field sensing elements can detect changes in bias magnetic field, but the magnetic field becomes non-uniform across the sensing area particularly over temperature
Solution Approach 1:
The patent applies local quality by creating two distinct magnetic field regions: a first magnetic field for sensing target position and a second magnetic field for self-test purposes. These fields are generated in different locations and serve different functions, allowing the sensing elements to operate in a controlled uniform field during self-test while maintaining the ability to detect non-uniform fields during normal operation.
Solution Approach 2:
The patent segments the magnetic field generation into separate functional components: a first magnetic field generator for sensing operations and a second magnetic field generator for self-test operations. This segmentation allows independent optimization of each field's characteristics, enabling uniform field generation for testing while maintaining the required field variations for target detection.
2Measurement precision
If concentrators are used to reduce non-uniformity of bias field, then magnetic field uniformity improves, but cost increases and minimum usable air gap is reduced
Solution Approach 1:
The patent extracts the self-test function from the main sensing operation by implementing a separate test mode that can be activated independently. This allows the system to perform accuracy verification without requiring additional concentrators or modifying the primary magnetic circuit design, thereby avoiding increased cost and reduced air gap.
Solution Approach 2:
The patent implements self-service by enabling the magnetic field sensor to test its own accuracy through integrated self-test circuitry and procedures. The sensor uses its own magnetic field generating capabilities to create test conditions and evaluate its performance, eliminating the need for external test equipment or additional structural components like concentrators.
3Measurement precision
If additional circuitry is added to compensate for different DC offsets, then measurement accuracy improves, but cost increases
Solution Approach 1:
The patent applies preliminary action by performing DC offset characterization and compensation parameter determination during the self-test mode before normal operation. The system pre-calculates compensation values that are then applied during sensing operations, eliminating the need for continuous complex compensation circuitry while maintaining measurement accuracy.
Solution Approach 2:
The patent changes operational parameters by switching between different operating modes: a self-test mode for characterization and a normal sensing mode for operation. During self-test, the system adjusts magnetic field parameters and measures DC offsets to determine compensation parameters, which are then used in normal operation without requiring additional hardware.
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
Enhances the accuracy of speed and direction detection in magnetic field sensors, reduces the need for additional circuitry, and maintains a larger air gap, thereby improving sensor performance and cost-effectiveness.
Implementation Method 1
magnetic field sensing elements used in an application for detecting a target are placed within the magnetic field formed by the back bias magnet. Thus, the magnetic field sensing elements detect changes in bias magnetic field caused by movement of the target
Data Source
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AI summary
Systems, methods, and apparatuses for magnetic field sensors with self-test include a detection circuit to detect speed and direction of a target. One or more circuits to test accuracy of the detected speed and direction may be included. One or more circuits to test accuracy of an oscillator may also be included. One or more circuits to test the accuracy of an analog-to-digital converter may also be included. Additionally, one or more IDDQ and/or built-in-self test (BIST) circuits may be included.