CMOS Biochip Matrix Array for DNA Detection
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Solution Overview
Problem
Conventional DNA detection methods using charge detection transistors in matrix arrays face challenges such as large operational amplifiers that cause noise and oscillation, high power source difficulties, and the need for extensive optical systems, which hinder the development of compact and high-throughput DNA sequencing and diagnostic tools.
Innovation Solution
A CMOS biochip with a matrix array of charge detection field effect transistors and a control circuit using CMOS current mirror circuits maintains constant current and voltage across each transistor, reducing cell size and improving detection accuracy, and integrating reference transistors and differential amplifiers to enhance sensitivity and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional operational amplifiers are used in each cell of the matrix array, then the detection range and sensitivity are improved, but the device area increases and noise and oscillation occur
Solution Approach 1:
The patent extracts the essential control functions (constant current supply and voltage regulation) from the conventional operational amplifier and implements them using separate, simplified circuit elements: a constant current source circuit and a voltage regulation circuit. This decomposition removes the problematic high-gain amplification stage that causes noise and oscillation while maintaining the necessary control capabilities for ISFET operation.
Solution Approach 2:
The patent uses a reference transistor to create a replicated control circuit that can be easily copied across multiple cells in the matrix array. The reference transistor-based constant current source and voltage regulation circuits provide identical control characteristics to each ISFET without requiring complex operational amplifiers in each cell, thereby reducing area while maintaining detection sensitivity.
2Measurement precision
If conventional operational amplifiers are used in each cell of the matrix array, then the detection range and sensitivity are improved, but noise and oscillation occur
Solution Approach 1:
The patent removes the high-gain amplification function from each cell that causes noise and oscillation, extracting only the essential control functions (constant current supply and voltage regulation). By using low-gain, stable circuits instead of operational amplifiers, the system achieves operational stability while maintaining detection sensitivity through differential measurement techniques.
3Measurement precision
If extensive optical systems are used for DNA detection, then detection accuracy is improved, but the device complexity and size increase
Solution Approach 1:
The patent replaces the mechanical/optical detection system with an electrical detection system using ISFETs. Instead of using optical components (lenses, detectors, light sources) to detect DNA binding events, the system uses ion-sensitive field effect transistors that directly convert chemical interactions at the gate into electrical signals, thereby eliminating complex optical systems while maintaining detection accuracy.
4Productivity
If the matrix array is integrated on a single chip, then productivity and throughput are improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality by making each cell in the matrix array self-contained with its own constant current source and voltage regulation circuits. This local autonomy allows each cell to operate independently with standardized design parameters, reducing the impact of global manufacturing variations. The reference transistor technique further enhances this by providing local reference points that compensate for process variations across the chip.
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 enables a compact, high-accuracy DNA detection system capable of identifying base sequences and detecting various substances, achieving high integration density and reducing power consumption while maintaining stable operation and minimizing noise.
Implementation Method 1
A charge detection transistor shown in FIG. 1 is used as an ISFET (ion sensitive field effect transistor) to detect an ion charge in a solution. This transistor is basically similar to a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) except that it does not have a gate electrode, and a gate insulating film is in direct contact with a solution 5 in which a reference electrode 6 is disposed.
Implementation Method 2
a control circuit including a CMOS current mirror circuit configured to control the charge detection field effect transistor such that a current flowing through the charge detection field effect transistor and a voltage across it are maintained constant
Implementation Method 3
a first differential amplifier configured to input an output signal depending on an operating state of the charge detection field effect transistor and an output signal depending on an operating state of the reference field effect transistor, and amplifies a difference between the two output signals
Data Source
AI summary
To realize a small size and high detection accuracy in a substance detection apparatus. A charge detection field effect transistor and a control circuit therefor are provided in each cell, and the control circuit controls the charge detection field effect transistor so that the drain-source voltage and the drain current of the charge detection field effect transistor are always maintained constant. The control circuit may be formed in a CMOS configuration including a small number of elements in a small area using a standard CMOS integrated circuit technique.