CHEMFET Array Pixel Integration Sigma-Delta ADC
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Solution Overview
Problem
Existing semiconductor-based devices for detecting chemical and biological reactions in electrolyte solutions, such as ISFETs, face limitations in simultaneous sampling and noise reduction due to the column parallel architecture, which requires external ADCs and results in inefficiencies in space usage and power consumption.
Innovation Solution
Integrating a sigma delta ADC within each pixel of the array, allowing for simultaneous sampling and digital conversion of ISFET signals, along with bias control and clocking arrangements to minimize noise and power usage, enabling scalable and high-resolution pixel arrays with increased density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If column parallel architecture with external ADCs is used, then hardware requirements are reduced, but simultaneous sampling capability is lost and noise reduction is insufficient
Solution Approach 1:
The patent divides the ADC function into individual segments, placing a separate ADC within each pixel rather than sharing a single ADC across multiple pixels. This segmentation enables each pixel to independently perform analog-to-digital conversion, allowing simultaneous sampling across the entire sensor array without the bottlenecks of shared resources.
Solution Approach 2:
The patent transitions from a column-parallel architecture where ADCs are positioned externally to a fully integrated architecture where ADCs are embedded within each pixel. This dimensional reorganization of the conversion function from external to internal enables simultaneous sampling while maintaining scalability through standardized pixel units.
2Area of stationary object
If ADCs are placed outside the sensor array, then space allocation is simplified, but chip space efficiency is reduced and pixel density is lowered
Solution Approach 1:
The patent merges the ADC functionality with the pixel structure by integrating the converter directly within each pixel unit. This consolidation eliminates the need for separate external ADC regions on the chip, thereby maximizing the use of chip area for active sensing elements and increasing overall pixel density.
Solution Approach 2:
The pixel structure is designed to be universal and self-contained, incorporating multiple functions including sensing, amplification, and analog-to-digital conversion within a single standardized unit. This multi-functional integration allows for efficient space utilization while maintaining scalability across different array sizes.
3Measurement precision
If higher resolution ADCs are used, then measurement precision improves, but noise from external sources increases
Solution Approach 1:
The patent extracts the analog-to-digital conversion function from the external readout circuitry and places it directly within each pixel. This extraction removes the high-impedance analog signal path that extends outside the pixel, eliminating a major source of noise interference and allowing higher resolution conversion without susceptibility to external electromagnetic interference.
Solution Approach 2:
The integrated ADC within each pixel acts as an intermediary that converts the analog signal to digital form immediately at the sensor location. This intermediate conversion step isolates the sensitive analog sensing node from external noise sources, as the digital output is inherently immune to electromagnetic interference that would affect external analog pathways.
Data Source
AI summary
An array of pixels, wherein each pixel comprises: a CHEMFET sensor; and a sigma delta ADC.