Dual-Gate ISFET Circuit for Precise Ion Concentration Sensing
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Solution Overview
Problem
Existing ion-sensitive field-effect transistors (ISFETs) face challenges in achieving high sensitivity and accuracy in measuring ion concentrations, particularly due to limitations in driver circuit design and the lack of microprocessors in analog circuit configurations.
Innovation Solution
The proposed ion sensing device incorporates a field-effect transistor with both a bottom gate and a top gate, along with a driver circuit that includes a constant current source and a voltage follower. This configuration supplies a constant reference potential to the reference electrode and applies a constant voltage across the output of the voltage follower and the bottom gate, enhancing the accuracy of ion concentration measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional ISFET driver circuit is used, then the circuit can be simple, but the measurement precision and sensitivity are insufficient
Solution Approach 1:
The driver circuit is segmented into distinct functional blocks: a constant current source block that supplies stable current to the ISFET drain, a voltage follower block that buffers the drain potential, and a control block that adjusts the bottom gate voltage. This segmentation allows each block to be optimized for its specific function, improving overall measurement precision while keeping the complexity manageable through modular design.
Solution Approach 2:
The voltage follower receives the drain potential as input and outputs a stabilized voltage that is fed back to control the bottom gate of the ISFET. This feedback mechanism ensures that the drain current remains constant despite variations in ion concentration, thereby improving measurement precision and sensitivity without requiring complex external control systems.
2Measurement precision
If microprocessors are used to control the driver circuit, then the measurement accuracy can be improved, but the device complexity increases
Solution Approach 1:
The driver circuit is designed to be self-regulating through the voltage follower feedback mechanism. The circuit automatically adjusts the bottom gate voltage based on the drain potential without requiring external microprocessor intervention. This self-service approach maintains high measurement precision while avoiding the complexity and cost associated with microprocessor-based control systems.
Solution Approach 2:
The patent replaces microprocessor-based electronic control with an analog voltage follower circuit that provides automatic feedback control. This substitution eliminates the need for digital processing, ADC/DAC converters, and programming, thereby reducing device complexity while maintaining measurement precision through continuous analog feedback.
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
The described configuration improves the accuracy and sensitivity of ion concentration measurements, allowing for precise determination of ion concentrations in sample solutions, while also simplifying the circuit design by eliminating the need for microprocessors.
Implementation Method 1
an electrical double layer is produced at the interface between the sample solution and the insulating film of the ISFET and the voltage of the electrical double layer changes the potential at the interface of the channel of the ISFET
Implementation Method 2
a voltage follower configured to receive a potential of the drain
Data Source
AI summary
Ion sensing device includes a field-effect transistor including a bottom gate and a top gate, a reference electrode, and a driver circuit configured to measure concentration of ions in a sample solution into which the reference electrode and the top gate are immersed. The driver circuit includes a constant current source configured to supply a drain of the field-effect transistor with a constant current, and a voltage follower configured to receive a potential of the drain. The driver circuit is configured to supply the reference electrode with a constant reference potential, apply a constant voltage across an output of the voltage follower and the bottom gate, and output an output potential of the voltage follower.