MEMS Inertial Sensor Frequency Sweep for Fast Resonance Lock
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Solution Overview
Problem
Existing inertial sensors with MEMS resonators face challenges in quickly locking to the resonant frequency due to large tolerances between MEMS and control electronics, requiring time-consuming and costly individual trimming processes.
Innovation Solution
A method where the control electronics oscillator is initially forced to a frequency below the MEMS resonator frequency, then ramps up while monitoring signal amplitude, switching to PLL mode when resonance is detected, allowing the system to lock to the MEMS resonator frequency in a short time without the need for individual calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the control electronics oscillator frequency is matched to the MEMS resonant frequency within tight tolerances, then the system can lock quickly without trimming, but the manufacturing precision and cost increase due to individual device trimming requirements
Solution Approach 1:
The system performs preliminary frequency sweeping before final locking to pre-establish the resonant frequency relationship. The oscillator sweeps through a frequency range to detect the MEMS resonant frequency, then locks to that detected frequency, eliminating the need for pre-matching or individual trimming during manufacturing.
Solution Approach 2:
The oscillator frequency is made dynamic rather than fixed, allowing it to sweep through a range and adapt to the actual MEMS resonant frequency. This dynamic adjustment capability enables the system to accommodate manufacturing tolerances without requiring tight initial matching or individual trimming.
2Ease of manufacture
If the control electronics oscillator frequency tolerance is increased to reduce manufacturing complexity, then production cost and time decrease, but the system requires individual trimming to achieve proper frequency matching
Solution Approach 1:
The system performs self-calibration by automatically detecting its own resonant frequency through the sweeping mechanism. The control electronics autonomously identify the MEMS resonant frequency and adjust the oscillator to match, eliminating the need for external trimming processes or manual calibration.
Solution Approach 2:
The system uses feedback from the MEMS resonator response to detect when the oscillator frequency matches the resonant frequency. The amplitude detection provides feedback that guides the sweeping process and determines when to stop sweeping and begin locking, ensuring accurate frequency matching without external intervention.
3Ease of manufacture
If frequency sweeping is implemented to detect resonant frequency, then individual trimming becomes unnecessary, but the initial frequency acquisition time increases during the sweeping process
Solution Approach 1:
The system rapidly sweeps through the frequency range to quickly identify the resonant frequency, then immediately locks onto it. The sweeping process is optimized to move quickly through non-resonant frequencies and pause only when resonance is detected, minimizing the overall time spent in the frequency acquisition phase.
Solution Approach 2:
The frequency sweeping is performed as a periodic initialization sequence that occurs only once when the system is first powered on or reset. After the initial sweep and lock, the system maintains the locked frequency without repeated sweeping, so the time penalty is incurred only during initialization rather than during continuous operation.
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 approach enables rapid and efficient locking to the MEMS resonator frequency, potentially eliminating the need for individual trimming and reducing production time and cost, while being applicable to various types of sensors.
Implementation Method 1
the MEMS resonator is driven into resonance by a suitable driver signal generated by control electronics
Implementation Method 2
monitoring the amplitude of the MEMS transducer signals. When the frequency of the MEMS resonance is reached an increase in the MEMS transducer signals is detected
Implementation Method 3
The control electronics then forces the oscillator frequency to ramp at a suitable speed while monitoring the amplitude of the MEMS transducer signals. When the frequency of the MEMS resonance is reached an increase in the MEMS transducer signals is detected and the control electronics stops the ramp of the oscillator frequency and switches to PLL (phase lock loop) mode
Implementation Method 4
switches to PLL (phase lock loop) mode. The frequency of the oscillator is now suitably close to the MEMS resonator frequency to allow the system to lock to the MEMS in a short period of time
Data Source
Figure 1
AI summary
An inertial sensor is described in which a resonant element is driven by control electronics into resonance. The control electronics includes an oscillator. A circuit is provided for matching the frequency of the oscillator with the frequency of the output of the resonant element such that the time to operation from start up of the sensor is minimised and the requirement of frequency matching a given sensor to the control electronics is removed.