MEMS Gyroscope Drive Circuit for Third-Harmonic Suppression
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Solution Overview
Problem
MEMS gyroscopes experience spurious harmonics due to non-idealities in the mechanical transfer function, leading to performance deterioration, particularly at frequencies like 3*f0, which are not effectively addressed by existing technologies.
Innovation Solution
A circuit and method that generates driving signals with controlled pulse durations and phase shifts to reduce the amplitude of spurious harmonics, specifically the third harmonic, by optimizing the timing of control signals to minimize spectral contributions at frequencies other than the resonance frequency f0.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional driving signals are used to excite the MEMS resonator, then the resonator can be driven at resonance frequency f0, but spurious harmonics (especially at 3*f0) are excited due to non-idealities in the mechanical transfer function
Solution Approach 1:
The patent applies periodic action by using a square wave driving signal with period T0 (equal to the resonance period at frequency f0) to excite the MEMS resonator. This periodic excitation is specifically designed to resonate at the fundamental frequency while minimizing harmonic content through precise timing control of the square wave transitions.
Solution Approach 2:
The patent changes the parameter of the driving signal from a conventional sinusoidal waveform to a square wave with optimized pulse widths. By adjusting the duty cycle and pulse duration parameters of the square wave signal to match the resonance characteristics, the system achieves enhanced resonance excitation while suppressing spurious harmonics at frequencies like 3*f0.
2Object-generated harmful factors
If the mechanical transfer function non-idealities are addressed by adding filtering stages, then spurious harmonics can be reduced, but the circuit complexity increases
Solution Approach 1:
The patent converts the harmful effect of mechanical transfer function non-idealities into a benefit by using a square wave driving signal whose spectral characteristics naturally align with the resonance frequency f0. The abrupt transitions of the square wave provide strong fundamental frequency content while the timing is optimized to minimize excitation of spurious harmonics, effectively using the signal's inherent properties rather than adding complex filtering.
Solution Approach 2:
The system achieves harmonic suppression through self-service by using the resonance characteristics of the MEMS device itself to filter the driving signal. The square wave excitation is timed such that the resonator's natural response at frequency f0 amplifies the desired signal while the mechanical system's own transfer function attenuates the spurious harmonics, eliminating the need for external filtering circuits.
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
The solution effectively reduces the amplitude of spurious harmonics, enhancing the stability and performance of MEMS gyroscopes without increasing circuit complexity, thereby improving the resonant oscillation of the movable mass.
Implementation Method 1
the first and the second driving signals D1, D2 cause the generation of electrostatic forces which act on the movable mass 20 and cause the driving mode to be excited under resonance conditions, so as to amplify the amplitude of the oscillation
Implementation Method 2
the movable mass 20 resonates along the X axis when forced to the frequency f0
Implementation Method 3
when the gyroscope 1 rotates about the Y direction, the movable mass 20 also oscillates along the Z direction, due to the Coriolis force which is generated when the gyroscope 1 rotates about the Y direction
Implementation Method 4
a first and a second position sensing signals I1, I2 are generated on the sensing electrodes 5, which are indicative of the position, along the X direction, of the movable mass 20; for example, the first and the second position sensing signals I1, I2 are differential signals generated by means of a capacitive sensing mechanism
Data Source
Figure 1
Figure 2~5
Figure 3
AI summary
Driving circuit for a driving resonator stage (4) of a MEMS gyroscope (1) including at least a first and a second electrode (31,32) and a movable mass (20), the driving circuit (3A,3B) including: a synchronization stage (16) which receives an electrical position signal (sPOS1) indicative of the position of the movable mass (20) and generates a reference signal (sLOCK') phase- and frequency-locked with the electrical position signal (sPOSl); a driving stage (2) which generates, on the basis of the reference signal (sLOCK'), a first and a second driving signal (D1,D2), which are applied to the first and, respectively, the second electrodes (31,32), so that the movable mass (20) is subject to a first and a second electrostatic force which cause the movable mass (20) to oscillate. Each of the first and the second driving signals (Dl,D2) comprises, for each period of the reference signal (sLOCK'), a corresponding pulse, the pulses of the first and the second driving signals (Dl,D2) being temporally alternated and having a same duration (α*T0), the ratio (α) between the duration and the period (T0) of the reference signal (sLOCK') falling in the range [0.3-0.37] or in the range [0.63-0.7].