Adaptive EIS Circuitry for Low-Power Electrochemical Cell Impedance
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Solution Overview
Problem
Existing electrochemical impedance spectroscopy (EIS) techniques for characterizing electrochemical cells are power-intensive and complex, particularly when operating at high frequencies, which is undesirable for battery-powered wearable devices.
Innovation Solution
Implementing adaptive EIS circuitry that adjusts the stimulus and measurement circuitry based on a score derived from the coherence and consistency of the estimated transfer function, allowing for accurate impedance determination across a broad frequency range using step or impulse signals, reducing power consumption and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency stimulation (in excess of 1 MHz) is used to characterize electrochemical cells, then measurement precision is improved, but power consumption increases and device complexity increases
Solution Approach 1:
The system dynamically adjusts the stimulus frequency based on the time constant characteristics of the electrochemical cell. Rather than using fixed high frequency stimulation, the frequency is adapted to match the specific cell properties, enabling accurate measurements at lower frequencies for cells with larger time constants while maintaining precision for cells requiring higher frequencies.
Solution Approach 2:
The patent changes the stimulus frequency parameter adaptively based on measured cell characteristics. By determining the time constant from initial measurements and using this to select appropriate stimulus frequencies, the system optimizes the frequency parameter to achieve necessary measurement precision while minimizing power consumption associated with high frequency operation.
2Measurement precision
If high frequency stimulation (in excess of 1 MHz) is used to characterize electrochemical cells, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The system employs dynamic frequency selection based on cell time constants, avoiding the need for complex fixed high-frequency circuitry. By adapting the stimulus frequency to match cell characteristics, simpler circuit components can be used while maintaining measurement accuracy across different cell types.
Solution Approach 2:
The patent modifies the stimulus frequency parameter based on determined cell properties, allowing the use of simpler circuit components operating at lower frequencies for many applications. This parameter adaptation eliminates the need for complex high-frequency DAC and ADC circuitry in cases where high frequency is not strictly necessary.
3Measurement precision
If traditional EIS with DAC and ADC is used, then measurement precision is maintained, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates the complex DAC and ADC components from the EIS measurement system. By using a simplified approach that determines impedance from voltage measurements across a known resistor without requiring full digital conversion chains, the system maintains measurement precision while removing unnecessary complexity.
Solution Approach 2:
Instead of using complex digital converters, the system uses a simplified measurement approach that copies the essential measurement function through voltage division and timing-based detection. This alternative implementation achieves the same measurement precision without requiring complex converter circuitry.
Data Source
AI summary
Circuitry for determining an impedance of an electrochemical cell comprising at least one first electrode and a second electrode, the circuitry comprising: drive circuitry configured to apply a stimulus to the electrochemical cell; sense circuitry configured to measure a response of the electrochemical cell to the stimulus; and processing circuitry configured to: determine an estimated transfer function of the electrochemical cell based on the stimulus and the response; determine a score for the estimated transfer function; and adjust the stimulus or circuitry used to measure the response based on the score.