MEMS Time Synchronization via Host Timestamping
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Solution Overview
Problem
Current portable computing devices with MEMS devices face issues of clock uncertainty and drift, leading to sample rate uncertainty and misalignment of data from distributed sensors, which affects applications like indoor navigation and gesture recognition.
Innovation Solution
A system and method for timing synchronization in MEMS-based systems, where MEMS devices receive a synchronization signal from the MEMS processor, allowing them to accurately align samples and compensate for sample rate uncertainties by storing local time information, ensuring uniform spacing of samples and improving data alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If MEMS devices use internal RC oscillator circuits to generate sample clocks, then device independence and ease of operation are improved, but clock accuracy and sample rate precision deteriorate (accuracy as poor as +/-40% and drift as large as 100 PPM per second)
Solution Approach 1:
The patent introduces a Host system as an intermediary that provides a reference clock signal to all MEMS devices. This mediator resolves the contradiction by allowing MEMS devices to maintain operational independence while achieving synchronized timing through the external reference clock, eliminating the +/-40% accuracy error of internal RC oscillators.
Solution Approach 2:
The patent segments the timing function into two parts: MEMS devices handle local sensing operations independently, while the Host system handles centralized time synchronization and correlation. This segmentation allows each component to specialize - MEMS devices focus on sensing while the Host manages precision timing, resolving the accuracy-ease of operation tradeoff.
2Measurement precision
If a shared clock is used to synchronize MEMS devices, then timing correlation between devices is improved, but power consumption increases due to distributed clock at much higher rate than MEMS sample frequency
Solution Approach 1:
The patent implements periodic time stamping where the Host system assigns time stamps to MEMS samples at the actual sample rate rather than continuously synchronizing clocks. This periodic action reduces power consumption significantly compared to continuous distributed clocking, while still maintaining precise timing correlation through the time stamp mechanism.
Solution Approach 2:
The patent replaces the mechanical/electrical distributed clock system with an information-based time stamping system. Instead of physically distributing high-frequency clock signals that consume power, the system uses digital time stamps to represent timing information, substituting a low-power information processing approach for a high-power hardware synchronization approach.
3Device complexity
If sample rate uncertainty exists in MEMS devices, then device simplicity is maintained, but data alignment and filter performance deteriorate (wider filter bandwidths required, misalignment of distributed sensor data)
Solution Approach 1:
The patent implements feedback by having the Host system measure the actual sample rates of individual MEMS devices using time stamps, then use this feedback information to correlate samples from different devices accurately. This feedback mechanism allows the system to compensate for sample rate variations without requiring complex hardware modifications to the MEMS devices themselves.
Solution Approach 2:
The Host system acts as an intermediary that receives samples from multiple MEMS devices with different sample rates, correlates them using measured timing information, and produces aligned output data. This mediator resolves the data alignment problem while allowing MEMS devices to remain simple without built-in synchronization complexity.
Data Source
AI summary
A method is provided for time synchronization in a MEMS (MicroElectroMecahnical system) based system having a MEMS processor and a plurality of MEMS devices. In a specific embodiment, the method includes, in the MEMS processor, transmitting a synchronization signal to the plurality of MEMS devices and saving a local time upon transmitting the synchronization signal. The MEMS processor also receives sampled data and time information from the plurality of MEMS devices, when the data and information become available. The method also includes, in one or more of the MEMS devices, receiving the synchronization signal from the MEMS processor and storing a local time upon receiving the synchronization signal. The MEMS device also performs a sensing operation and stores sampled sense data and sense time information.