ISFET Driver Circuit for Stable Reference Potential Sensing
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Solution Overview
Problem
Ion-sensitive field-effect transistors (ISFETs) face limitations in sensitivity and accuracy for ion concentration measurement, particularly due to variations in the potential of the reference electrode and the need for complex driver circuits with microprocessors or analog circuit elements.
Innovation Solution
An ion sensing device with a field-effect transistor and a driver circuit that supplies a constant current to the drain and uses a voltage follower to maintain a constant reference potential, allowing for accurate measurement of ion concentration by fixing the reference electrode potential and utilizing analog circuit elements without a microprocessor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference electrode is used in ISFET measurement, then ion concentration can be measured, but the potential of the reference electrode varies causing measurement errors
Solution Approach 1:
The patent introduces a voltage follower circuit as an intermediary between the reference electrode and the ISFET gate. This voltage follower maintains a constant reference potential by buffering the reference electrode signal, thereby isolating the measurement system from potential fluctuations in the reference electrode and improving measurement accuracy
Solution Approach 2:
The patent changes the electrical parameter configuration by applying a constant voltage between the voltage follower output and the ISFET gate, rather than directly connecting the reference electrode to the gate. This parameter change stabilizes the gate potential and eliminates the direct influence of reference electrode potential variations on the measurement
2Measurement precision
If driver circuits with microprocessors or complex analog circuit elements are used, then measurement control is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the microprocessor and complex analog circuit elements from the driver circuit, retaining only the essential voltage follower and constant voltage source components. This simplification maintains adequate measurement control while significantly reducing device complexity and improving reliability
Solution Approach 2:
The voltage follower circuit automatically maintains the constant reference potential through its inherent buffering capability, and the constant voltage source self-regulates the gate potential, eliminating the need for complex control algorithms or microprocessor-based regulation
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 configuration enhances the accuracy and sensitivity of ion concentration measurement, reduces measurement errors, and enables concurrent measurement of multiple ion types with a single reference electrode, improving the overall performance of ISFETs in pH measurement and biosensing applications.
Implementation Method 1
a voltage follower configured to receive a potential of the drain
Implementation Method 2
a constant current source configured to supply a drain of the field-effect transistor with a constant current
Implementation Method 3
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 4
The theoretical maximum sensitivity of the ISFET is 58.16 mV/mol (T=293.15K), according to the Nernst equation
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.