Silicon-Cap Photodiode Accelerometer for Motion-Corrected PPG
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Solution Overview
Problem
Existing wearable devices face challenges in accurately measuring plethysmograph (PPG) signals due to low frequency noise and motion interference, necessitating a solution that integrates optical measurements with corroborating acceleration measurements to improve signal quality and efficiency.
Innovation Solution
A modified MEMS accelerometer with integrated silicon photodiode in the silicon cap, which allows for optical measurement while occupying no additional space, and is mounted on an ASIC for synchronized data read-out, reducing noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate devices are used for PPG measurement and acceleration measurement, then functional versatility is improved, but device complexity and space requirements increase
Solution Approach 1:
The patent combines a photodiode and accelerometer into a single integrated device housed in one capsule. The photodiode is positioned at the top of the capsule while the accelerometer is mounted on the bottom, sharing common electronics and housing. This merging approach provides both optical measurement capability and acceleration sensing in a single unit, reducing overall system complexity while maintaining functional versatility.
Solution Approach 2:
The integrated device performs multiple functions simultaneously: it measures light intensity for PPG signals, detects acceleration for motion tracking, and provides motion correction for improved PPG accuracy. By making the device multi-functional, it eliminates the need for separate dedicated sensors, thereby reducing device complexity while preserving adaptability.
2Measurement precision
If low frequency noise filtering is applied to improve PPG signal accuracy, then measurement precision is improved, but loss of useful low frequency information increases
Solution Approach 1:
The patent uses acceleration data as feedback to dynamically correct PPG signals. By measuring motion through the accelerometer and using this information to compensate for motion-induced artifacts in the PPG signal, the system can maintain high measurement precision without applying aggressive frequency filtering that would remove useful low frequency physiological information.
Solution Approach 2:
The acceleration sensor acts as an intermediary that provides motion information to correct the PPG signal. Instead of directly filtering the PPG signal and risking loss of physiological information, the system uses the intermediary acceleration measurements to indirectly account for and correct motion effects, preserving both signal accuracy and useful frequency content.
3Measurement precision
If multiple separate sensors are used for optical and acceleration measurements, then measurement comprehensiveness is improved, but power consumption increases
Solution Approach 1:
The patent merges the photodiode and accelerometer into a single integrated unit with shared electronics, housing, and power supply. This consolidation reduces the total power consumption compared to operating separate dedicated sensors, while still providing comprehensive optical and acceleration measurements for accurate PPG signal processing.
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 integrated system provides improved PPG signal accuracy and reduced power consumption by mitigating noise and synchronizing optical and acceleration measurements, enabling better estimation of physiological parameters like blood oxygen and pressure.
Implementation Method 1
a photodiode having a top portion and bottom portion disposed in and comprised by the cap
Data Source
AI summary
A novel, modified MEMS accelerometer with additional ability to measure optical radiation due to integration of silicon photodiode in the silicon cap. The silicon cap is used to protect the MEMS based accelerometer from the environment. The function of the cap is enhanced to include optical measurement. The entire sensor element including accelerometer and photodiode (XL+PD) occupies no more space than the XL alone.