Digital MEMS Gyroscope Control Without PLLs or High Clock Rates
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Solution Overview
Problem
MEMS gyroscopes face challenges with analog signal processing, including inaccuracy due to component parameter variations, difficulty in calibration, and high power consumption, particularly in digital control circuits requiring high clock frequencies.
Innovation Solution
A fully digital control circuitry for MEMS gyroscopes is introduced, featuring a digital primary loop with a first analog-to-digital converter and an infinite impulse filter for phase shifting, and a digital secondary loop with phase shifting filters and coherent detection, reducing the need for a PLL and minimizing clock frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PLL is used in the digital control circuit, then frequency stability is improved, but silicon area and power consumption increase
Solution Approach 1:
The patent extracts and removes the PLL (Phase-Locked Loop) component from the digital control circuit. By eliminating the PLL, the invention achieves the same frequency stability through alternative means (using the resonator's natural frequency and digital filtering), thereby reducing silicon area and power consumption while maintaining the required frequency stability for gyroscope operation.
Solution Approach 2:
The patent combines the frequency control function with the resonator structure itself. Instead of using a separate PLL circuit to control frequency, the invention integrates frequency determination directly into the resonator's natural oscillation characteristics, merging what were previously separate functions into a unified system that reduces component count and area.
2Speed
If high clock frequency is used in digital control circuits, then processing speed is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic clock frequency adjustment where the clock frequency adapts to the actual operating conditions of the gyroscope. By using the resonator's natural frequency as the reference and adjusting the sampling rate dynamically based on signal characteristics, the system maintains adequate processing speed while minimizing power consumption by avoiding unnecessarily high fixed clock frequencies.
Solution Approach 2:
The invention changes the clock frequency parameter from a high fixed value to a dynamically adjusted value based on the resonator's operating frequency. This parameter change allows the digital control circuit to process signals effectively while consuming less power, as the clock frequency matches the actual signal frequency rather than operating at a consistently high rate.
3Device complexity
If analog signal processing is used, then circuit complexity is reduced, but measurement precision deteriorates due to component parameter variations
Solution Approach 1:
The patent replaces the mechanical/analog signal processing system with a digital one. By converting analog signals to digital form and performing processing in the digital domain, the invention eliminates the sensitivity to component parameter variations that plagues analog circuits, while maintaining or even improving measurement precision through software-based filtering and signal processing algorithms.
Solution Approach 2:
The invention changes the signal processing domain from analog to digital, fundamentally altering how signals are handled. This parameter change allows for precise control of filtering characteristics, gain, and other processing parameters through digital means, achieving high measurement precision without the component tolerance issues that affect analog circuits.
4Measurement precision
If digital control circuitry is introduced, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes complex analog control circuitry (such as PLLs and analog filters) from the system, replacing them with simplified digital implementations. By taking out these complex analog components and using digital signal processing instead, the invention achieves high measurement precision while actually reducing overall control circuit complexity through the use of standard digital logic and software algorithms.
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 angular velocity detection, low sensitivity to component variations, and reduced power consumption, while omitting the need for a PLL, thus reducing silicon area and improving noise tolerance.
Implementation Method 1
a first infinite impulse filter configured to cause a −90-degree phase shift of the digitized primary signal on 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 an oscillating gyroscope is subjected to an angular motion, an undulating Coriolis force results. This creates a secondary oscillation orthogonal to the primary motion and to the axis of the angular motion, and at the frequency of the primary oscillation
Data Source
AI summary
A digital control circuitry for a MEMS gyroscope is provided. The digital control circuitry comprises a digital primary loop circuitry configured to process a digitized primary signal, a digital secondary loop circuitry configured to process a digitized secondary signal and a digital phase shifting filter circuitry configured to generate two phase shifted demodulation signals from the digitized primary signal. The digital secondary loop is configured to demodulate the digitized secondary signal using the two phase shifted demodulation signals.