MEMS Sensor Offset Cancellation Using Dynamic Feedback Gain
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Solution Overview
Problem
Micro-electromechanical system (MEMS) sensors introduce offsets that are not effectively removed by existing technologies, especially during startup and normal operation, affecting the accuracy of sensor readings.
Innovation Solution
A device and method utilizing an offset cancellation module with a digital-to-analog converter and a negative feedback system to remove DC offsets by adjusting the gain of the system and using a sign detector, integrator, and divider to dynamically adjust the offset cancellation process across multiple modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-pass filter is used to remove offset, then offset removal is achieved, but the response speed during startup and normal operation is slow
Solution Approach 1:
The patent implements dynamic offset cancellation by switching between different operational modes (startup mode and normal operation mode) with different integration times. During startup, a shorter integration time enables faster response, while during normal operation, a longer integration time provides more accurate offset cancellation. This dynamic adaptation resolves the contradiction between response speed and offset removal accuracy.
Solution Approach 2:
The system changes the integration time parameter based on operational phase. The integration time is adjusted from a first value during startup to a second value during normal operation, allowing the system to optimize both response speed and offset cancellation performance at different times.
2Measurement precision
If the offset cancellation integrates over a long period, then offset removal accuracy is improved, but the startup time increases
Solution Approach 1:
The system performs preliminary offset cancellation during startup using a first integration time that is sufficient for initial calibration but shorter than the full integration time used during normal operation. This preliminary action allows the system to become operational quickly while still achieving acceptable offset cancellation, with further refinement occurring during normal operation.
Solution Approach 2:
The integration time is dynamically adjusted based on the operational phase. During startup, a shorter first integration time reduces startup time, while during normal operation, a longer second integration time improves offset cancellation accuracy. The system transitions between these two states to balance speed and accuracy requirements.
3Measurement precision
If the gain is increased to improve offset cancellation, then offset removal effectiveness is improved, but asymmetric saturation of the MEMS sensor occurs
Solution Approach 1:
The gain is dynamically adjusted based on the operational phase and signal conditions. During startup, a first gain value is applied that provides sufficient offset cancellation without causing saturation. During normal operation, the gain is adjusted to a second value that optimizes offset cancellation while monitoring for saturation conditions. This dynamic control prevents the harmful effects of excessive gain while maintaining cancellation effectiveness.
Solution Approach 2:
The system uses feedback from the digitally filtered output signal to control the offset cancellation process. The sign of the output signal drives the digital-to-analog converter, and the offset cancellation module continuously adjusts the gain based on the feedback signal, preventing asymmetric saturation by reducing gain when approaching saturation limits.
Data Source
AI summary
The present disclosure is directed to a system that includes a sensor and a signal conditioner coupled to the sensor. The signal conditioner includes signal processing circuitry coupled to the sensor and offset cancellation circuitry. The offset cancellation circuitry includes a sign detector configured to output a high signal or a low signal based on a sign of an output signal from the signal processing circuitry, an integrator coupled to the sign detector, and a divider coupled to the integrator and to an input of the signal processing circuitry.