Differential PMOS ISFET pH Sensor with CMOS Integration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
ISFET-based pH sensors face limitations in widespread commercial use due to non-idealities such as size, weight, response time, and sensitivity, and require cost-effective, mass-producible designs that integrate signal processing for enhanced performance.
Innovation Solution
A differential pH sensor system utilizing p-channel ion-sensitive transistors with operational-transconductance-amplifiers (PIOTA) and n-channel load transistors, where the substrate voltage can be controlled to adjust sensitivity, integrated into a CMOS chip for miniaturization and improved noise performance, allowing for mass production without post-processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ISFET-based sensors are used for pH detection, then pH measurement capability is achieved, but sensitivity and response time are insufficient
Solution Approach 1:
The patent combines the ISFET sensor element with an operational transconductance amplifier (OTA) and n-channel load transistor to form an integrated PIOTA circuit. This merging of sensing and signal processing components on a single CMOS chip enhances sensitivity through active amplification while maintaining fast response characteristics inherent to solid-state ISFET technology.
Solution Approach 2:
The patent utilizes substrate biasing techniques where the n-type substrate voltage is adjusted to modulate the sensitivity of the p-channel IST. By changing the electrical parameter (substrate voltage) of the sensor, the measurement sensitivity can be optimized without affecting the physical structure or response time characteristics.
2Volume of moving object
If sensor size is reduced for portability, then miniaturization is achieved, but noise performance deteriorates
Solution Approach 1:
The patent integrates the ISFET sensor, OTA, and load transistors into a single monolithic CMOS chip structure. This consolidation eliminates the need for discrete components and interconnections that would increase size and introduce noise, achieving miniaturization while maintaining noise performance through on-chip signal processing.
Solution Approach 2:
The operational transconductance amplifier serves as an intermediary component that actively compensates for noise effects. The OTA provides low-noise amplification of the sensor signal while rejecting common-mode noise, enabling small sensor size without sacrificing noise performance.
3Ease of manufacture
If CMOS fabrication is used for mass production, then manufacturing cost and scalability are improved, but integration complexity increases
Solution Approach 1:
The patent designs the sensor system using universal CMOS standard cell library components (p-channel IST, n-channel load transistors, OTA) that can be fabricated using standard CMOS processes. This universality enables mass production through established semiconductor manufacturing while managing integration complexity through modular design.
Solution Approach 2:
The patent segments the sensor system into distinct functional modules: p-channel ion-sensitive transistors for sensing, n-channel load transistors for current conversion, and operational transconductance amplifiers for signal amplification. This segmentation allows each module to be independently optimized and integrated using standard CMOS design flows, reducing overall integration complexity.
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 solution provides a monolithic, portable, and robust pH sensing method with enhanced sensitivity, fast response, and ease of miniaturization, capable of measuring pH across various ranges with improved noise rejection and temperature stability, suitable for commercial applications.
Implementation Method 1
a first p-channel ion-sensitive transistor (IST)-operational-transconductance-amplifier (PIOTA) and a second PIOTA
Data Source
AI summary
A pHI sensor system, Integrated Circuit (IC) chip, and a method are provided. Embodiments of the pH sensor may a first p-channel ion-sensitive transistor (IST)-operational-transconductance-amplifier (PIOTA) and a second PIOTA. Each PIOTA may further include a p-channel IST, an n-channel load transistor having a source and drain, wherein each PIOTA may have a drain-to-source resistance different from each other. Each PIOTA may further include an operational-transconductance-amplifier (OTA). A differential sensor may be connected to the outputs of both PIOTAs, and an output from the differential sensor may indicate a change in pH. Each PIOTA may further have an n-type substrate, a potential of which may be varied to control sensitivity of pH change detection. The NMOS load transistors of one or both of the PIOTAs may be selected from a plurality of NMOS load transistors to enhance sensitivity.