Hall Sensor Signal Rotation to Suppress Interference Folding
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Solution Overview
Problem
Hall sensor-based data acquisition systems face challenges in reducing high frequency interference, which degrades the signal-to-noise ratio due to rotation artifacts and offset voltages, especially when multiple aggressor signals are present, and require careful frequency planning to avoid folding back of high frequency signals into the signal band.
Innovation Solution
A data acquisition system that periodically rotates the signal from the Hall effect sensor and resets state variables in synchronization with rotation, effectively synthesizing a zero in the signal transfer function at multiples of the rotation frequency to attenuate interfering signals, using a multiplexer, amplifier, ADC, and digital filters to enhance frequency response and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Spinning Current Modulation is used to reduce offset voltages, then offset reduction is achieved, but high frequency interference signals fold back into the signal band degrading SNR
Solution Approach 1:
The patent applies periodic Spinning Current Modulation to rotate the Hall element terminals at a specific frequency (e.g., 90 kHz), which periodically converts DC offset into AC signals at the rotation frequency. This periodic action allows the offset to be moved to a known frequency where it can be filtered, while the patent carefully selects the rotation frequency to avoid interference folding into the signal band.
Solution Approach 2:
The patent converts the harmful effect of high frequency interference folding into a benefit by carefully selecting the spinning frequency such that folded interference falls outside the signal bandwidth. The harmful folding effect is transformed into a predictable frequency transformation that can be managed through proper frequency planning and filtering.
2Measurement precision
If multiple aggressor signals are present, then frequency planning becomes insufficient, but system complexity increases
Solution Approach 1:
The patent introduces an intermediary approach by using a single dominant spinning frequency that creates a predictable mixing pattern. Instead of trying to plan for each individual aggressor signal, the system uses the spinning modulation as an intermediary transformation that moves all interference to predictable frequencies that can be filtered by a low-pass filter, simplifying the handling of multiple aggressors.
Solution Approach 2:
The patent changes the frequency domain parameters of the signal through spinning modulation, transforming the measurement problem from one of direct DC measurement to AC measurement at the spinning frequency. This parameter transformation allows the system to reject low-frequency drift and DC offsets while maintaining sensitivity to the actual measurement signal.
3Measurement precision
If differential amplifier offset and 1/f noise are reduced, then measurement accuracy improves, but circuit design complexity increases
Solution Approach 1:
The patent uses periodic chopping of the differential amplifier at the spinning frequency to modulate the amplifier's offset and 1/f noise to the spinning frequency. This periodic action transforms the amplifier's low-frequency errors into AC signals that can be filtered by the low-pass filter, allowing the use of standard amplifiers without requiring ultra-low offset designs.
Solution Approach 2:
The patent converts the harmful effect of amplifier offset and 1/f noise into a benefit by modulating these errors to the spinning frequency through chopping. The errors that would normally degrade DC measurement accuracy are transformed into AC signals at a known frequency where they can be easily rejected by frequency-selective filtering.
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 effectively nullifies or attenuates high frequency aggressor signals, improving the signal-to-noise ratio and reducing the impact of rotation artifacts, as demonstrated by a 30 dB attenuation of aggressor signals and harmonics, thereby enhancing the accuracy of measured voltage.
Implementation Method 1
Hall sensor-based data acquisition systems
Data Source
AI summary
A data acquisition system (DAS) for acquiring data from a Hall effect sensor includes one or more state variables, a multiplexer that periodically rotates a signal from the Hall effect sensor, and a controller that resets the one or more state variables in synchronization with rotation of the signal. The state variables may be digital states in a digital memory or voltages of capacitors the controller forces to a reset voltage. The state variables may be included in a noise-shaping SAR ADC, a delta-sigma ADC, a digital filter, an integrator, an analog filter, a VCO, an incremental ADC or an auxiliary ADC-assisted incremental ADC, or an auxiliary ADC of the DAS.