MEMS Offset Cancellation Circuit for Fast Startup Accuracy
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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 dynamically adjust the gain and remove DC offsets from MEMS sensor outputs, employing a sign detector, integrator, and divider to adjust slew rates and integration intervals across multiple operational 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 two modes: a first mode during startup that quickly establishes offset cancellation, and a second mode during normal operation that maintains cancellation while allowing signal throughput. This dynamic switching resolves the contradiction between accurate offset removal and fast response speed.
Solution Approach 2:
The system changes the operational parameters of the offset cancellation circuit by switching between different modes with different gain settings and time constants. During startup, parameters are set for fast offset cancellation; during normal operation, parameters are adjusted to maintain cancellation while preserving signal bandwidth, thus resolving the speed-accuracy tradeoff.
2Measurement precision
If offset cancellation is implemented during startup and normal operation, then sensor accuracy is improved, but circuit complexity increases
Solution Approach 1:
The offset cancellation circuit is designed to perform multiple functions: it operates during startup to establish offset cancellation, continues operating during normal operation to maintain accuracy, and integrates with the existing MEMS sensor interface circuitry. This multi-functionality approach improves sensor accuracy without requiring completely separate dedicated circuits for each operation phase.
Solution Approach 2:
The patent employs a feedback mechanism where the output of the MEMS sensor is fed back through the offset cancellation circuit, which dynamically adjusts the offset compensation based on the sensed signal. This feedback approach maintains high accuracy while using a compact circuit architecture that leverages the existing signal path rather than adding complex independent correction circuits.
3Measurement precision
If dynamic gain adjustment is used to counteract offset, then offset cancellation effectiveness is improved, but control complexity increases
Solution Approach 1:
The offset cancellation circuit performs self-adjustment by automatically detecting the offset condition and modifying its own gain settings through the feedback mechanism. The system serves itself by using the sensed output to automatically control the offset cancellation parameters, eliminating the need for external complex control logic or manual calibration procedures.
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.