Closed-Loop Magnetic Field Sensor With Distance-Based Current Feedback
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Solution Overview
Problem
Conventional magnetic field sensors face challenges in maintaining linear operation and efficient power consumption due to large offset levels and varying sensitivity of magnetoresistance elements, particularly when detecting targets at different distances.
Innovation Solution
A closed loop magnetic field sensor with a feedback path that includes an emitter coil drive circuit and a reference coil, allowing for dynamic adjustment of emitter current based on distance to the target, using a combiner to combine reflected and reference fields, and a transconductance module to generate an output current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional magnetic field sensors use fixed emitter current, then device complexity is reduced, but measurement precision deteriorates due to non-linear operation at varying distances
Solution Approach 1:
The patent implements a feedback control system where the sensor output is fed back to dynamically adjust the emitter coil current. The controller monitors the sensor output signal and modifies the emitter current in real-time to maintain linear operation of the magnetoresistance element, thereby improving measurement precision across varying air gaps while managing device complexity through integrated control circuitry.
Solution Approach 2:
The system transitions from static fixed current operation to dynamic current adjustment. The emitter coil current is continuously adapted based on the detected air gap distance, allowing the sensor to maintain optimal linear operation conditions regardless of target distance, thus resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If conventional magnetic field sensors operate at high current levels, then measurement precision is maintained across all distances, but use of energy increases significantly
Solution Approach 1:
Instead of applying excessive current levels continuously, the system applies partial current adjustment based on actual measurement needs. The feedback controller reduces emitter current when high precision is not required and increases it only when measurement accuracy demands, thereby maintaining measurement precision while significantly reducing overall energy consumption compared to constant high-current operation.
3Device complexity
If magnetoresistance elements operate outside linear range, then device complexity is reduced, but measurement precision deteriorates due to offset levels and varying sensitivity
Solution Approach 1:
The feedback control system actively monitors the sensor output and adjusts the emitter coil current to keep the magnetoresistance element operating within its linear range. This prevents operation in non-linear regions that would cause offset errors and sensitivity variations, thereby maintaining measurement precision without requiring complex additional compensation circuitry.
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 efficient power consumption and linear operation across varying distances by dynamically adjusting emitter current, minimizing residual offset and maximizing dynamic range, thus improving sensor accuracy and efficiency.
Implementation Method 1
an emitter coil drive circuit for outputting an emitter current to an emitter coil for generating an emitter field
Implementation Method 2
a reference coil drive circuit for outputting a reference current to a reference coil for generating a reference field
Implementation Method 3
Hall effect elements are one type of magnetic field sensing elements that generate a variable voltage in response to changes in an applied or sensed magnetic field
Implementation Method 4
Magnetoresistance elements are another type of magnetic field sensing element that has a variable resistance that changes in response to changes in an applied or sensed magnetic field
Data Source
AI summary
Method and apparatus for a closed loop CAPS magnetic field sensor having an emitter coil current that corresponds to a distance from a target. An emitter coil drive circuit outputs an emitter current to an emitter coil for generating an emitter field and a reference coil drive circuit outputs a reference current to a reference coil for generating a reference field. The combined fields generate an applied field and a magnetic field sensing element generates an electric signal. The sensor has a closed loop configuration with a feedback path that includes the emitter coil drive circuit and the emitter coil and is configured to modify an amplitude of the emitter current signal based on a distance from the target to the magnetic field sensing element.