AC Hall Sensor Offset Suppression via Harmonic Extraction
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Solution Overview
Problem
Current Hall effect sensors for AC magnetic fields require complex switching circuitry to mitigate offset and induced signals, which limits frequency measurement and increases size and cost, and are not effective in systems with dynamically changing magnetic fields.
Innovation Solution
A Hall effect sensor driven with an AC current at frequency fA, where the output Hall signal component is measured at 2fA, eliminating the need for switching to suppress parasitic offset and induced signals, allowing for higher frequency measurement and smaller, cost-effective systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If switching circuitry is used to mitigate offset and induced signals in Hall effect sensors, then measurement accuracy is improved, but device complexity and size increase
Solution Approach 1:
The patent extracts and eliminates the switching circuitry from the Hall effect sensor system by using a different measurement approach. Instead of using switches to mitigate offset and induced signals, the invention uses a four-terminal configuration with specific current reversal sequences that achieve the same signal mitigation without requiring additional switching components, thereby reducing device complexity while maintaining measurement accuracy
Solution Approach 2:
The patent makes the Hall effect sensor terminals multi-functional. The same four terminals are used for both current injection and voltage measurement, and the terminals serve different functions at different time periods during the measurement sequence. This eliminates the need for separate switching circuitry to redirect signals, as the terminals themselves are reconfigured through controlled current reversal
2Measurement precision
If switching circuitry is used to suppress parasitic signals, then measurement accuracy is improved, but the measurable frequency range is limited
Solution Approach 1:
The patent implements dynamic current reversal sequences that adapt to the measurement requirements. The current direction is reversed at different terminals at different time periods, creating a dynamic measurement protocol that eliminates the need for high-speed switching circuitry. This dynamic approach allows the system to measure higher frequencies because the limitation is set by the measurement protocol timing rather than by physical switching component speed limits
3Measurement precision
If switching circuitry is used to mitigate offset signals, then measurement accuracy is improved, but system size and component count increase
Solution Approach 1:
The patent merges the offset mitigation function into the basic sensor structure by using the same four terminals for both current injection and voltage measurement. The offset suppression is achieved through the measurement protocol that reverses current direction at different terminals, rather than through separate switching components. This merging of functions eliminates additional components while maintaining the ability to suppress offset signals
4Measurement precision
If conventional Hall effect measurement is used with switching, then offset suppression is achieved, but induced signals from time-varying magnetic fields are not effectively suppressed
Solution Approach 1:
The patent employs periodic current reversal sequences applied at different terminals during different time periods of the measurement cycle. This periodic action at strategically timed intervals creates measurement sequences that are insensitive to both DC offset and AC induced signals. The induced signals, being time-varying, are suppressed because the measurement protocol samples at phases where the induced voltage contribution is minimized or cancels out
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
This approach enables measurement of higher frequencies without frequency limitations, reduces system size and component count, and provides accurate magnetic field strength measurement and spectrum analysis in dynamic environments.
Implementation Method 1
Hall effect sensors for time-varying magnetic fields
Data Source
AI summary
We provide a Hall effect sensor driven with an AC current where the output Hall signal component is at the second harmonic. More specifically, the drive current is at fA and the relevant Hall signal frequency component is at 2fA. The resulting measurement is of the magnetic field strength at fA. This eliminates the need for switching to suppress the parasitic offset signal. This approach also leads to suppression of the induced signal caused in the Hall sensor by the time varying magnetic field.