Multi-axis MEMS IMU Using Frequency Modulation for Temperature Decoupling
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Solution Overview
Problem
Conventional MEMS inertial measurement units (IMUs) face limitations in temperature and vibration sensitivity, signal stability, dynamic range, and bandwidth, preventing them from meeting navigation grade requirements due to their reliance on analog amplitude modulation and separate fabrication of gyroscopes and accelerometers.
Innovation Solution
A multi-axis MEMS IMU using frequency modulated (FM) accelerometers and gyroscopes, which enables simultaneous detection and decoupling of inertial inputs and temperature distribution, providing ultra-high precision, stability, and wide dynamic range through self-calibration and robustness against mechanical and electromagnetic interferences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MEMS sensors use analog amplitude modulation to detect inertial inputs, then the sensor output is proportional to the input, but the system suffers from limited dynamic range, temperature sensitivity, and vibration sensitivity
Solution Approach 1:
The patent replaces the conventional analog amplitude modulation readout system with a frequency modulation system based on resonant oscillation. The resonant frequency of the MEMS structure is modulated by the inertial input, and this frequency modulation is detected using a phase-locked loop (PLL) circuit. This substitution eliminates the temperature and vibration sensitivity inherent in analog AM systems while achieving ultra-high dynamic range exceeding 150 dB.
Solution Approach 2:
The patent changes the operating parameter from amplitude modulation to frequency modulation. By measuring changes in resonant frequency rather than amplitude, the system achieves immunity to temperature and vibration effects that primarily affect amplitude. The frequency measurement provides stable, high-precision detection with dynamic range exceeding 150 dB.
2Measurement precision
If high precision gyroscope operates in vacuum, then measurement precision is improved, but packaging complexity increases due to vacuum sealing requirements
Solution Approach 1:
The patent merges the gyroscope and accelerometer onto a single MEMS chip with common proof mass and readout electronics. This integration allows both sensors to share the same vacuum environment, eliminating the need for separate vacuum packaging for the gyroscope. The unified design reduces packaging complexity while maintaining high precision for both sensor types.
Solution Approach 2:
The patent creates a universal sensor platform that performs both gyroscope and accelerometer functions using a single MEMS structure with common proof mass. This multi-functional design simplifies packaging requirements, as only one vacuum-sealed environment is needed instead of separate packages for each sensor type.
3Speed
If accelerometer operates at atmospheric pressure, then bandwidth is improved, but gyroscope performance degrades due to lack of vacuum
Solution Approach 1:
The patent combines both gyroscope and accelerometer operations within the same vacuum environment on a single chip. The accelerometer is designed to operate effectively in vacuum, and both sensors share common vacuum packaging and readout electronics. This integration eliminates the pressure compromise, allowing the gyroscope to maintain high precision in vacuum while the accelerometer achieves adequate bandwidth through optimized mechanical design.
4Measurement precision
If multiple single-axis sensors are assembled on PCB, then IMU performance is improved through off-axis rejection, but miniaturization is limited due to separate fabrication and packaging
Solution Approach 1:
The patent integrates multiple inertial sensors (gyroscopes and accelerometers) onto a single MEMS chip with shared proof mass and readout electronics. This monolithic integration dramatically reduces the IMU footprint compared to PCB assembly of separate sensors, while maintaining performance through precise fabrication and common-mode rejection of off-axis inputs.
Solution Approach 2:
The patent employs a nested structure where multiple sensor functions are embedded within a single MEMS device. The common proof mass serves multiple sensing functions, and the integrated readout electronics are embedded within the same chip package, creating a compact nested architecture that minimizes overall device volume.
5Ease of manufacture
If conventional AM sensors are used, then manufacturing is simplified, but stability and vibration immunity are poor
Solution Approach 1:
The patent replaces the analog amplitude modulation readout system with a frequency modulation system using resonant oscillation and phase-locked loop detection. This substitution dramatically improves signal stability and vibration immunity while maintaining compatibility with standard MEMS fabrication processes. The frequency-based readout is inherently more robust to mechanical disturbances and temperature variations.
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 FM IMU achieves unprecedented resolution and stability, with temperature characterization showing less than 0.2% variation and dynamic range of 156 dB, and frequency stability of 0.15 ppb, significantly improving upon state-of-the-art conventional AM systems.
Implementation Method 1
The IMU is based upon frequency modulated (FM) accelerometers and gyroscopes... An FM resonant accelerometer for generating frequency modulated (FM) accelerometer output signals... An FM vibratory gyroscope for generating frequency modulated (FM) gyroscopic output signals
Implementation Method 2
An FM vibratory gyroscope for generating frequency modulated (FM) gyroscopic output signals fabricated in the silicon chip
Implementation Method 3
An FM resonant accelerometer for generating frequency modulated (FM) accelerometer output signals fabricated in the silicon chip
Data Source
AI summary
A multi-axis microelectromechanical-systems (MEMS) inertial measurement unit (IMU) is fabricated in a vacuum sealed single packaged device. An FM vibratory gyroscope and an FM resonant accelerometer both for generating FM output signals is fabricated in the silicon chip using MEMS. A signal processor is coupled to the an FM vibratory gyroscope and to the FM resonant accelerometer for receiving the FM gyroscopic output signals and the FM accelerometer output signals. The signal processor generates simultaneous and decoupled measurement of input acceleration, input rotation rate, and temperature and/or temperature distribution within the IMU, self-calibration of the biases and scale factors of the IMU and its support electronics against temperature variations and other common mode errors, and reduction of the cross axis sensitivity by reducing acceleration errors in the gyroscope and rotation errors in the accelerometer.