Magnetic Field Sensor Self-Test Circuit for Offset Compensation
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Solution Overview
Problem
Magnetic field sensors with back bias magnets often face non-uniform magnetic fields due to temperature variations, leading to different DC offsets for each sensor, which requires additional costly circuitry for compensation and can reduce the minimum usable air gap when using concentrators to mitigate this issue.
Innovation Solution
An apparatus with detection circuits, test circuits, and analog-to-digital converters to accurately determine speed and direction of a target, including a counter for error detection, a ramp generator for oscillator testing, and a comparator for ADC accuracy, allowing for self-testing and reducing the need for additional compensation circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a back bias magnet is used to generate the magnetic field, then the magnetic field sensing elements can detect changes in bias magnetic field caused by movement of the target, but the magnetic field becomes non-uniform across the sensing area particularly over temperature, leading to different DC offsets for each sensor
Solution Approach 1:
The patent implements self-test circuits that automatically detect and compensate for DC offsets without requiring external intervention. The test circuits generate test signals, measure the sensor responses, and calculate compensation values internally, allowing the sensor system to self-correct for non-uniform magnetic fields and temperature variations.
Solution Approach 2:
The patent performs DC offset compensation measurements during initialization or calibration phases before actual sensing operations. By pre-characterizing the offset errors and storing compensation values, the system eliminates the need for complex real-time compensation circuitry during normal operation.
2Stability of the object's composition
If concentrators are used in conjunction with back bias magnets to reduce the non-uniformity of the bias field, then the magnetic field uniformity improves, but the minimum usable air gap is reduced and the magnetic circuit cost increases
Solution Approach 1:
The patent compensates for magnetic field non-uniformity by digitally adjusting sensor output parameters based on measured DC offsets. Instead of physically modifying the magnetic circuit with concentrators, the system changes the electrical parameters (offset compensation values) to correct for field variations, maintaining air gap and reducing magnetic circuit complexity.
3Stability of the object's composition
If concentrators are used to reduce magnetic field non-uniformity, then the bias field uniformity improves, but the manufacturing cost of the magnetic circuit increases
Solution Approach 1:
The patent replaces mechanical/magnetic solutions (concentrators) with electronic/digital compensation methods. Instead of adding physical magnetic components to uniform the field, the system uses electronic test circuits and digital signal processing to measure and compensate for non-uniformity, significantly reducing manufacturing cost and complexity.
4Measurement precision
If additional circuitry is added to compensate for different DC offsets, then the sensor accuracy improves, but the cost of the magnetic field sensor increases
Solution Approach 1:
The patent combines the test/compensation circuitry with the main sensor signal processing path. The same analog-to-digital converters and processing logic are used for both normal sensing operations and offset measurements, eliminating the need for separate dedicated compensation hardware and reducing overall circuit cost.
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 enables accurate detection of speed and direction with reduced complexity and cost by incorporating self-test capabilities within the magnetic field sensor system, effectively managing non-uniform magnetic fields and maintaining a larger air gap.
Implementation Method 1
Magnetic field sensors including a magnetic field sensing element, or transducer, such as a Hall Effect element or a magnetoresistive element
Implementation Method 2
Magnetic field sensors including a magnetic field sensing element, or transducer, such as a Hall Effect element or a magnetoresistive element
Data Source
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.