MEMS Gyro Motor Loop Filter with Twin-Tee Notch
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Solution Overview
Problem
Current motor drive control loops for MEMS gyroscopes suffer from weak suppression of undesired mechanical modes of vibration, which delays the startup time due to inadequate phase shift and gain characteristics in existing filter topologies.
Innovation Solution
A minus-90-degree phase-shift twin-tee notch filter is implemented in the motor drive loop circuit to provide a flat phase shift over a wider frequency range, rapid phase transition, and strong attenuation at specific frequencies, effectively suppressing undesired mechanical modes and enhancing the startup time of the MEMS gyro motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional filter topology is used in the motor drive control loop, then the circuit complexity is low, but the suppression of undesired mechanical modes is weak and startup time is delayed
Solution Approach 1:
The patent changes the electrical parameters of the filter circuit by introducing a switching element that dynamically alters the filter's transfer function. The filter transitions between different parameter states (different pole locations in the s-plane) to achieve strong suppression of undesired modes during startup, then switches to a state that maintains stability during operation, thereby resolving the contradiction between suppression effectiveness and startup time
Solution Approach 2:
The filter topology is made dynamic through the switching element that changes the filter characteristics based on operational phase. During motor startup, the switching element configures the filter to provide strong attenuation at undesired mechanical mode frequencies. Once the motor reaches steady state, the switching element transitions the filter to a different configuration. This dynamic adaptation allows the system to achieve both fast startup (through strong initial suppression) and stable operation
2Reliability
If the filter provides strong attenuation at undesired modes, then suppression effectiveness improves, but the phase shift accuracy at motor resonance frequency may be compromised
Solution Approach 1:
The filter design segments the frequency response into distinct regions: one optimized for suppressing undesired mechanical modes and another optimized for providing accurate -90 degree phase shift at the motor resonance frequency. The switching element enables the filter to operate in different segmented configurations depending on the operational requirements, achieving both strong suppression and accurate phase shift without compromise
Data Source
AI summary
A motor drive loop circuit for a micro-electro-mechanical system (MEMS) gyroscope is provided. The motor drive loop circuit includes a motor configured to drive a proof mass in the MEMS gyroscope and a minus-90-degree phase-shift twin-tee notch filter. The motor is configured to cause the proof mass to oscillate at a primary-proof-mass mode. The a minus-90-degree phase-shift twin-tee notch filter is configured to: provide a minus 90 degree phase at a motor resonance frequency equal to the primary-proof-mass mode; suppress resonance at undesired mechanical modes of the motor during a startup of the motor; and provide gain at the motor resonance frequency.