MEMS Gyroscope In-Band Beating Removal via Digital Clock
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Solution Overview
Problem
Existing vibrating MEMS gyroscopes face challenges in accurately measuring angular rotation rates due to noise interference caused by phase shifts in the sample clock signal, particularly when the clock frequency is close to an integer multiple of the drive frequency, leading to in-band beating that degrades noise performance.
Innovation Solution
The introduction of a digital sample clock generator that generates an in-phase sample clock without using a phase-locked loop (PLL), allowing for phase shifting and clock frequency adjustment to avoid critical frequency ratios, thereby reducing noise interference and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase-locked loop (PLL) is used to generate the sample clock signal, then the clock frequency can be locked to the drive frequency, but noise interference and in-band beating occur when the clock frequency is close to an integer multiple of the drive frequency
Solution Approach 1:
The patent changes the clock frequency parameter by introducing a frequency offset Δf such that the sample clock frequency fs satisfies fs = N·fd + Δf, where N is an integer and Δf is a small offset frequency. This parameter change moves the clock frequency away from critical integer multiples of the drive frequency, eliminating the in-band beating phenomenon while maintaining accurate angular rotation rate measurement.
2Stability of the object's composition
If the sample clock frequency is set close to an integer multiple of the drive frequency, then phase synchronization is improved, but in-band beating degrades noise performance
Solution Approach 1:
The patent modifies the clock frequency parameter by introducing a controlled offset Δf from the integer multiple of the drive frequency. This parameter adjustment maintains sufficient phase synchronization for accurate measurement while avoiding the critical frequency ratios that cause in-band beating and noise performance degradation.
3Reliability
If the clock frequency is adjusted to avoid critical frequency ratios, then noise performance is improved, but phase synchronization may be affected
Solution Approach 1:
The patent introduces a small frequency offset Δf that is sufficient to eliminate in-band beating but small enough to maintain adequate phase synchronization. This optimized parameter change balances noise performance improvement with preservation of phase synchronization stability for accurate angular rate measurement.
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
This solution effectively minimizes noise-induced degradation in angular rate measurements by shifting the clock frequency to avoid critical frequency ratios, resulting in improved noise performance and more accurate determination of angular rotation rates.
Implementation Method 1
A force acting on the gyroscope mass may be induced as a capacitive force by applying a voltage to the capacitor plates of the drive actuation unit
Implementation Method 2
A Coriolis force will apply to the gyroscope mass in the presence of an angular rotation. The Coriolis force is proportional to the velocity of the gyroscope mass, its angular rate of rotation and its mass, and perpendicular to the direction of movement
Implementation Method 3
the amplitude of the movement may be measured by sampling the drive measurement signal once every period at extremes of the drive measurement signal by the use of a phase-locked loop (PLL) to determine an in-phase clock with an appropriate phase relative to the drive measurement signal
Data Source
AI summary
Vibration gyroscope circuitry, connectable to a vibrating MEMS gyroscope, includes drive circuitry for driving the gyroscope and a measurement circuit for providing a drive measurement signal indicating displacement of a mass along a drive axis. Sense circuitry processes a sense measurement signal of the gyroscope indicating displacement of the mass along a sense axis. A digital sample clock generator includes an oscillator for generating a master clock, a counter for counting master clock periods during one period of an input signal derived from the drive measurement signal, and a number count monitor for determining during how many input signal periods the number count stays constant and for comparing a number of constant periods with a critical number of constant periods. A frequency shifter triggers the oscillator to shift the master clock frequency whenever the monitor determines that the number of constant periods exceeds the critical number of constant periods.