Electrochemical Cell Impedance Measurement Circuit
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Solution Overview
Problem
Existing electrochemical impedance spectroscopy (EIS) techniques require high power and complex circuitry to measure characteristics at high frequencies, which is undesirable for battery-powered devices like wearable sensors due to increased power consumption and complexity.
Innovation Solution
The implementation of novel circuitry that reduces power consumption by using a lower ADC sample rate and employing a square wave stimulus with co-prime signal and sampling frequencies to minimize aliasing and harmonic interference, allowing for accurate impedance measurement with reduced ADC sampling frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency stimulation is used to measure electrochemical cell characteristics, then measurement precision is improved, but power consumption and device complexity increase
Solution Approach 1:
The patent applies periodic square wave stimulation at multiple frequencies to characterize the electrochemical cell. By using periodic excitation signals with known frequencies and analyzing the periodic response, the system achieves accurate impedance measurements without requiring continuous high-frequency operation, thereby reducing overall power consumption while maintaining measurement precision.
Solution Approach 2:
The patent replaces traditional high-speed analog-to-digital converters and complex high-frequency signal generation circuits with a microcontroller-based digital signal processing approach. The microcontroller generates stimulation signals and processes responses using software algorithms, substituting complex hardware with a more power-efficient computational system that achieves the same measurement objectives.
2Measurement precision
If high frequency stimulation is used to measure electrochemical cell characteristics, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a multi-functional microcontroller-based system that combines signal generation, signal conditioning, analog-to-digital conversion, and impedance calculation in a single integrated device. This universal platform performs multiple functions that would traditionally require separate dedicated circuits, thereby reducing overall device complexity while maintaining high measurement precision through software-based signal processing.
Solution Approach 2:
The patent replaces complex analog circuitry including high-frequency function generators, precision operational amplifiers, and high-speed ADCs with a microcontroller-based digital system. The microcontroller generates stimulation waveforms digitally, acquires responses through a single ADC, and computes impedance characteristics through software algorithms, dramatically simplifying the hardware architecture while preserving measurement accuracy.
3Measurement precision
If ADC sample rate is increased to accurately capture high frequency responses, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent changes the measurement approach by using lower frequency square wave stimulation signals instead of high-frequency sinusoidal signals. This parameter change allows the use of lower ADC sample rates while still capturing the essential impedance characteristics of the electrochemical cell. The microcontroller adjusts stimulation frequency and ADC sampling rate dynamically, optimizing power consumption for each measurement condition.
Solution Approach 2:
The patent uses periodic square wave stimulation with frequencies optimized for the specific electrochemical cell characteristics being measured. By synchronizing the ADC sampling with the periodic stimulation signal and using correlation-based analysis, the system achieves high measurement precision at lower sample rates, significantly reducing ADC power consumption compared to continuous high-rate sampling.
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, the stimulus having a stimulation frequency and a stimulation amplitude; and measurement circuitry configured to: sample an output of the electrochemical cell at a sampling frequency to generate an output signal; determine an output amplitude of output signal at one or more alias frequencies, the one or more alias frequency based on the stimulation frequency and the sampling frequency; and determine the impedance of the cell at the stimulation frequency based on the output amplitude at the one or more alias frequencies and the stimulation amplitude; and control circuitry configured to: control the sampling frequency and the stimulation frequency such that a Nyquist rate of the sampling frequency is greater than stimulation frequency.