Electrochemical Cell Measurement Circuit with Calibration and Offset Control
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Solution Overview
Problem
Existing electrochemical sensors face errors due to non-ideal effects at the electrochemical cell and sub-optimal circuitry conditions, leading to inaccuracies in measuring analyte concentrations.
Innovation Solution
The circuitry includes measurement circuitry with a transimpedance amplifier and a feedback resistor, coupled with a first and second ADC, and control circuitry that operates in calibration and measurement modes to adjust gain and offset signals, using offset current injection and autozeroing to minimize errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement circuitry is used without calibration, then device complexity is reduced, but measurement precision deteriorates due to non-ideal effects and sub-optimal circuitry conditions
Solution Approach 1:
The system performs calibration measurements before actual analyte measurements to characterize non-ideal effects. The calibration mode measures offset signals and non-linearity parameters in advance, which are then used to correct subsequent measurement signals, thereby improving measurement precision without requiring complex real-time correction circuitry
Solution Approach 2:
The system uses measured calibration data to generate correction factors that are applied to measurement signals. The control circuitry compares measurement signals against calibration-derived thresholds and applies appropriate corrections, creating a feedback loop that continuously improves measurement accuracy based on characterized system behavior
2Measurement precision
If signal processing is performed without maintaining signal levels within range, then device complexity is reduced, but measurement precision deteriorates due to non-linearity
Solution Approach 1:
The system characterizes the non-linear response of the measurement circuitry during calibration mode by applying known test signals and measuring the actual output. This preliminary characterization allows the system to create lookup tables or correction curves that map expected linear responses to actual non-linear responses, enabling accurate signal processing without complex real-time linearization circuitry
Solution Approach 2:
The system changes the operating parameters of the measurement circuitry by applying different signal levels during calibration to map out the non-linear response. By characterizing the response across different parameter ranges (signal amplitudes, frequencies), the system can interpolate or extrapolate correction factors for actual measurement signals, maintaining accuracy across varying conditions
3Measurement precision
If calibration and measurement modes are implemented, then measurement precision is improved, but loss of time increases due to mode switching
Solution Approach 1:
The system implements periodic calibration where the calibration mode is activated at scheduled intervals rather than continuously. The control circuitry switches between calibration and measurement modes in a periodic fashion, performing calibration measurements at predetermined times while conducting analyte measurements during intermediate periods, thus balancing accuracy maintenance with measurement throughput
Solution Approach 2:
The system performs partial calibration by measuring only the essential parameters needed for correction (such as offset and gain factors) rather than comprehensive characterization. This selective calibration approach obtains sufficient correction data with minimal calibration time, accepting that some higher-order non-linearities may not be fully corrected in exchange for reduced calibration duration
4Measurement precision
If offset current injection is used to maintain signal levels, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The system applies offset current periodically rather than continuously, injecting correction currents only when needed to maintain signal levels within the optimal range for the ADC. The control circuitry monitors signal levels and activates offset current injection in pulses or intervals, reducing overall power consumption compared to continuous offset application while maintaining measurement precision during critical measurement windows
Data Source
AI summary
Circuitry for measurement of electrochemical cells Circuitry for processing an analyte signal obtained from an electrochemical cell. the circuitry comprising: measurement circuitry having a first input coupled to a first electrode of the electrochemical cell, the measurement circuitry configured to convert the analyte signal at the first electrode to a first analog output signal; a first analog-to-digital converter (ADC) having an first ADC input for receiving the first analog output signal, the first ADC configured to convert the first analog output signal to a first digital output signal at a first ADC output; drive circuitry; and control circuitry, wherein the circuitry is operable in one or more of a calibration mode and a measurement mode, wherein, in the calibration mode, the drive circuitry is configured to apply a calibration signal at the first input of the measurement circuitry, the control circuitry configured to calibrate the measurement circuitry based on the first analog output signal or the first digital output signal responsive to the calibration signal, and wherein, in the measurement mode, the drive circuitry is configured to apply an offset signal at the first input of the measurement circuitry, the control circuitry configured to control the offset signal to maintain the first analog output signal or the first digital output signal within a threshold range.