Sigma-Delta ADC Current Mirror for Electrochemical Sensor Power Reduction
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Solution Overview
Problem
Conventional electrochemical sensors face high power consumption due to high input capacitance, which complicates the operation of active integrators in measuring analyte concentrations using potentiostats.
Innovation Solution
The system employs a current mirror, voltage regulator, capacitor, comparator, and counter to replicate the input current, allowing for the measurement of a mirror current instead of the direct input current, thereby reducing capacitance-related power issues, and uses a sigma-delta ADC to generate a digital output based on the mirror current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an active integrator is used to integrate the input current, then the current can be converted to a voltage signal, but the high input capacitance results in high power consumption
Solution Approach 1:
The patent uses a current mirror to create a copy of the input current from the working electrode. Instead of directly integrating the high-capacitance input current, the circuit mirrors this current to a separate path where it can be integrated by a passive integrator (capacitor), thereby avoiding the power consumption issue while maintaining measurement accuracy.
Solution Approach 2:
The current mirror acts as an intermediary between the high-capacitance working electrode and the integration circuit. It transfers the current information without requiring the integrator to directly handle the high input capacitance, thus reducing power consumption while preserving the measurement function.
2Use of energy by moving object
If a current mirror is used to replicate the input current, then power consumption is reduced, but the device complexity increases
Solution Approach 1:
The current mirror circuit performs multiple functions: it replicates the input current for integration, provides impedance transformation, and isolates the high-capacitance electrode from the integration circuit. This multi-functionality justifies the added complexity by solving multiple problems simultaneously.
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 reduces power consumption and enables accurate measurement of analyte concentrations with improved efficiency in electrochemical sensors, suitable for applications like eye-mountable devices for monitoring tear film analytes.
Implementation Method 1
The current mirror is coupled to the working electrode and is configured to develop a mirror current that mirrors the input current
Implementation Method 2
The capacitor is coupled to the current mirror and current source, and is configured to develop a capacitor voltage in response to at least the mirror current and control current
Implementation Method 3
The comparator is coupled to the capacitor and is configured to output a waveform based on variations of the capacitor voltage relative to a comparison voltage
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
A potentiostat includes a voltage regulator, a current mirror, a capacitor, a comparator, a current source, and a counter. The voltage regulator maintains a voltage on a working electrode of an electrochemical sensor. The current mirror develops a mirror current that mirrors an input current from the working electrode. The capacitor is alternately charged by the mirror current, causing the capacitor voltage to increase at a rate related to the current's magnitude, and discharged by a control current, causing the capacitor voltage to decrease. The comparator outputs a waveform that includes upward and downward transitions based on the variations of the capacitor voltage. The current source produces the control current based on the waveform. The counter counts the number of upward or downward transitions in the waveform during a predetermined sampling period to produce a digital output. The digital output is representative of the magnitude of the input current.