Switched Capacitor Accumulator for Hematocrit Impedance Measurement
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Solution Overview
Problem
Handheld blood glucose and hemoglobin meters face challenges in accurately measuring blood glucose levels due to interference from hematocrit concentration, which affects the accuracy of glucose measurements and requires efficient energy and processing power management with limited resources.
Innovation Solution
The system employs a switched capacitor accumulator to measure hematocrit impedance by calculating magnitude and phase measurements using a low-cost, low-power microcontroller, allowing for accurate phase angle determination at high frequencies, and adjusts glucose measurements based on the calculated interferent impedance to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a small coin cell battery is used to keep cost and size down, then device portability and affordability are improved, but battery life becomes insufficient and requires extremely infrequent battery changes
Solution Approach 1:
The system uses periodic action by implementing impedance measurements at multiple discrete frequency points (e.g., 50 kHz, 100 kHz, 200 kHz, 500 kHz) rather than continuous measurement. The microcontroller sequentially excites the test strip at these frequency points and accumulates phase measurements over multiple cycles, enabling accurate hematocrit determination with minimal energy consumption from the coin cell battery.
Solution Approach 2:
The system maintains continuity of useful action through the switched capacitor accumulator that continuously accumulates phase measurements over the measurement window. This accumulation process ensures that useful measurement action continues throughout the sampling period, maximizing information extraction from each battery-powered measurement cycle and extending effective battery life.
2Measurement precision
If impedance measurement at multiple frequency points is implemented to determine hematocrit, then measurement accuracy is improved, but energy consumption and processing power requirements increase
Solution Approach 1:
The system applies segmentation by dividing the impedance measurement into discrete frequency segments (e.g., 50 kHz, 100 kHz, 200 kHz, 500 kHz). Each frequency point is measured separately with dedicated excitation and accumulation cycles. This segmentation enables accurate hematocrit determination through multi-frequency analysis while managing energy consumption by concentrating measurements at specific points rather than continuous sweeping.
Solution Approach 2:
The system changes parameters by varying the excitation frequency across multiple discrete values to extract hematocrit information. The microcontroller modifies the frequency parameter systematically through the switched capacitor accumulator, enabling accurate interferent characterization through parameter variation while controlling energy use through discrete rather than continuous parameter changes.
3Measurement precision
If phase measurement accumulation over a sample window is used to measure small phase angles, then measurement sensitivity is improved, but measurement time increases
Solution Approach 1:
The system implements preliminary action by pre-configuring the switched capacitor accumulator with reference frequencies and measurement windows before actual sampling. The microcontroller prepares the accumulation registers and timing sequences in advance, so that when a blood sample is applied, the phase accumulation can begin immediately without setup delays, reducing overall measurement time while maintaining sensitivity.
Solution Approach 2:
The system applies partial action by accumulating phase measurements over a limited sample window at selected frequency points rather than continuously monitoring all frequencies. This partial accumulation approach provides sufficient sensitivity for small phase angle detection while limiting the total measurement time to clinically acceptable durations.
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 enhances the accuracy of glucose measurements by accounting for hematocrit interference, extends battery life in handheld devices, and maintains low power consumption, ensuring reliable and precise glucose monitoring.
Implementation Method 1
measuring a phase angle of the impedance using a switched capacitor accumulator to accumulate time differences that represent phase over a sample window
Implementation Method 2
measuring an impedance of the blood sample at a plurality of frequency points between 10 kilohertz and 500 kilohertz, including a magnitude measurement and the phase measurement
Data Source
AI summary
There is provided a system for measuring a property of a sample that comprises a test strip for collecting the sample; a diagnostic measuring device configured to receive the test strip and measure a concentration of an analyte in the sample received on the test strip; and the diagnostic measuring device further comprising a processor programmed to execute an analyte correction for correcting a measurement of the sample due to one or more interferents, comprising: calculating an interferent impedance measurement including a magnitude measurement and a phase measurement using a switched capacitor accumulator to measure a phase angle; and adjusting the measurement of the analyte in the sample using that the calculated interferent impedance measurement.