Magnetic Field Sensor Chopping Scheme Shared ADC
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Solution Overview
Problem
Magnetic field sensors using Hall Effect elements often exhibit undesirable DC offset voltage, which existing techniques like chopping partially address but may not fully suppress, especially in time-shared ADC configurations where sampling time differences introduce additional errors.
Innovation Solution
The proposed solution involves specific chopping schemes and sequences that arrange samples in time across different channels of a magnetic field sensor to ensure they have the same center of mass, allowing for equivalent interpolation as if all samples were taken at the same time, thereby suppressing low-frequency flicker noise without the need for extra logic or storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a time-shared ADC is used to reduce cost and complexity, then device complexity is reduced, but measurement precision deteriorates due to sampling time differences between channels
Solution Approach 1:
The patent applies periodic chopping action to the magnetic field sensing elements, switching them between different operational states at specific frequencies. This periodic modulation allows samples from different channels to be taken at systematically arranged time points that share a common center of mass, enabling accurate demodulation and interpolation to compensate for the time-shared ADC's sampling delays.
2Measurement precision
If conventional chopping is applied to reduce DC offset, then offset voltage is reduced, but low-frequency flicker noise is not sufficiently suppressed
Solution Approach 1:
The patent employs asymmetric chopping sequences where samples are deliberately arranged with different time offsets for different channels, but configured to have a common center of mass. This asymmetric time arrangement, combined with specific demodulation techniques, creates frequency response characteristics that suppress low-frequency flicker noise while maintaining offset cancellation capability.
Solution Approach 2:
The patent changes the temporal parameters of the chopping sequence by arranging samples at specific time points that satisfy the common center of mass condition. By adjusting the timing and sequence of samples across different channels, the system modifies the frequency response to achieve both offset cancellation and flicker noise suppression.
3Device complexity
If samples from different channels are taken at different times, then device complexity is reduced, but reliability deteriorates due to errors from sampling time differences
Solution Approach 1:
The patent implements a feedback mechanism through demodulation and interpolation processes that compensate for the time differences in sampling. By calculating the center of mass of sample times and using this information to guide the demodulation process, the system corrects for timing errors and reconstructs accurate measurements despite the time-shared ADC's sequential sampling.
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 reduces errors due to sampling time differences and suppresses low-frequency flicker noise, improving the accuracy and reliability of magnetic field sensors, especially in configurations with shared ADCs.
Implementation Method 1
magnetic field sensing elements, such as Hall Effect elements
Data Source
AI summary
Methods and apparatus for magnetic field sensor having a sample chopping with a shared ADC. A sensor may include receiving a chopping sequence for samples from first and second channels that share an analog-to-digital converter (ADC) in a magnetic field sensor. The samples for the first and second channel are timed with respect to a virtual sampling time (VST), such that a sum of the sample times for the samples for the first channel is equal to the VST, and a sum of the sample times for the samples for the second channel is equal to VST.