Digital Force Feedback Loop for MEMS Gyroscope Quadrature Error
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Solution Overview
Problem
MEMS gyroscopes face challenges with quadrature error motion and non-linearity due to imperfections in primary and secondary oscillations, leading to inaccuracies in angular rate detection, and existing digital solutions require high clock frequencies, increasing power consumption and circuit area.
Innovation Solution
A fully digital control circuitry for MEMS gyroscopes is introduced, featuring a secondary sense loop with a digital low pass infinite impulse response filter for phase shifting and force feedback, reducing the need for a PLL and minimizing power consumption by using a low clock frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a PLL is used for frequency synthesis and phase control in the secondary sense loop, then frequency accuracy and phase control are improved, but device complexity and power consumption increase
Solution Approach 1:
The patent extracts the PLL functionality from the secondary sense loop, removing the phase-locked loop circuitry entirely. Instead, a simple digital oscillator generates the reference frequency, and a digital filter performs phase control. This extraction eliminates the complex PLL components while maintaining the essential frequency synthesis and phase control functions through simpler digital circuits.
Solution Approach 2:
The patent replaces the traditional analog/hybrid PLL system with a fully digital implementation. The digital oscillator and digital filter substitute for the analog voltage-controlled oscillators, phase detectors, and loop filters of a conventional PLL. This substitution reduces complexity and power consumption while achieving the same frequency synthesis and phase control objectives.
2Measurement precision
If a PLL is used for frequency synthesis and phase control, then frequency accuracy is improved, but power consumption increases
Solution Approach 1:
The patent extracts the power-consuming PLL components from the system. By removing the voltage-controlled oscillators, phase detectors, and analog loop filters that require continuous power supply, the design significantly reduces power consumption. The essential frequency synthesis function is maintained through a low-power digital oscillator that only consumes power when generating the reference frequency.
Solution Approach 2:
The patent substitutes the high-power analog PLL system with a low-power digital implementation. Digital circuits consume less power than their analog counterparts, especially when operating at lower frequencies. The digital filter replaces the analog loop filter, and the digital oscillator replaces the analog VCO, collectively reducing power consumption while maintaining frequency accuracy through digital signal processing.
3Speed
If high clock frequency is used in digital control circuitry, then processing speed is improved, but power consumption and circuit area increase
Solution Approach 1:
The patent applies partial action by using a low clock frequency that is sufficient for the required processing speed. Instead of using a high clock frequency that would provide excessive processing capability, the design uses the minimum necessary frequency to achieve the required angular rate measurement accuracy. This partial action approach reduces power consumption and circuit area while meeting the performance requirements.
4Speed
If high clock frequency is used in digital control circuitry, then processing speed is improved, but circuit area increases
Solution Approach 1:
The patent uses partial action by implementing digital filters with lower sampling frequencies than would be required for high-speed processing. The filter design uses a sampling frequency that is sufficient to achieve the required measurement accuracy but lower than what would be needed for maximum processing speed. This reduces the circuit area required for digital logic elements while maintaining adequate performance for angular rate detection.
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 enables precise detection of angular velocity, reduces sensitivity to component parameter variations, and achieves good noise tolerance while minimizing circuit area and power consumption, allowing for accurate angular rate measurement without the need for a complex PLL.
Implementation Method 1
a digital low pass infinite impulse response filter configured to cause a -90 degreed phase shift to the digitized secondary signal at a resonance frequency of a mechanical resonator of the MEMS gyroscope
Implementation Method 2
A mass-spring structure typically exhibits a resonance or a resonant behavior by naturally oscillating at some frequencies, called as its resonant frequencies, with greater amplitude than on other frequencies
Implementation Method 3
When a mass is driven in one direction and rotational angular velocity is applied about axis orthogonal to driven axis, the mass experiences a force in orthogonal direction with respect to both driven and rotated axes as a result of the Coriolis force
Data Source
AI summary
A secondary sense loop for a MEMS gyroscope comprises a secondary element comprising at least one mechanical resonator, an analog front end circuitry, a digital secondary loop circuitry and an analog back end circuitry. The digital secondary loop circuitry comprises a signal path receiving at its input an analog secondary input signal representing a detection motion of a mechanical resonator and providing at its output an output signal indicating an angular velocity said MEMS gyroscope is subject to, said signal path comprising an analog-to-digital converter configured to digitize the analog secondary input signal into a digitized secondary signal, and a digital force feedback circuitry controlling operation of a closed force feedback loop configured to adjust response function of the secondary sense loop.