Switchable Low Pass Filter for Angular Velocity Sensor Offset Bias
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Solution Overview
Problem
Tuning fork vibration type angular velocity sensors suffer from offset bias errors due to factors like power supply variations, temperature fluctuations, and external impacts, leading to inaccuracies in detected angles, which existing calibration methods struggle to effectively address.
Innovation Solution
A sensor IC that includes a detector for angular velocity signals, an AD converter, a DC component detector, and a corrector to estimate and cancel offset bias by identifying the DC component in the digital signal, utilizing a low pass filter and amplifier to adjust cutoff frequencies and gain for efficient zero-point correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low pass filter with low cutoff frequency is used to detect DC component, then measurement precision of offset bias is improved, but response time increases
Solution Approach 1:
The patent applies dynamics by making the low pass filter cutoff frequency adjustable rather than fixed. The filter switches between a first cutoff frequency (higher) for rapid response and a second cutoff frequency (lower) for accurate DC component detection. This dynamic adjustment allows the system to optimize between response speed and measurement precision at different operational stages.
2Loss of time
If low pass filter cutoff frequency is switched from high to low, then response time is reduced, but output signal continuity is broken due to gain variation
Solution Approach 1:
The patent implements feedback by using a gain correction circuit that monitors the output signal and automatically adjusts the gain after cutoff frequency switching. The gain correction circuit receives the filter output and applies compensation to maintain continuous signal levels, ensuring that the transition between high and low cutoff frequencies does not create signal discontinuities.
3Measurement precision
If zero-point correction is performed using averaging method, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the DC component detection function from complex averaging algorithms and implements it through a dedicated low pass filter circuit. By separating the DC component extraction into a simple analog filter stage before the ADC, the system achieves zero-point correction without requiring complex digital signal processing or multiple sampling operations, thus reducing overall device complexity.
Data Source
AI summary
A IC for sensor includes a detector which detects an angular velocity signal based on a signal from a sensor element, an AD converter which converts an analog signal from the detector into a digital signal, and a DC component detector which detects a DC component from the digital signal output from the AD converter within a predetermined period of time.