TFT Pixel Array CDS Circuit for Threshold Voltage Compensation
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Solution Overview
Problem
Conventional optical sensor apparatuses using Thin Film Transistor (TFT) technology on glass substrates suffer from large variations in threshold voltages (VTH) among different TFTs and over the lifetime of the apparatus, and existing solutions fail to adequately support pixel sensor circuits while minimizing the size and number of electrical connections in the signal interface with silicon ICs.
Innovation Solution
A light sensing apparatus incorporating a pixel array with TFTs and an interface integrated circuit featuring silicon transistors, including correlated double sampling (CDS) circuits with capacitors, hold TFTs, and control circuits to manage timing operations, reducing the impact of VTH variations by using current sources and receivers to process light signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TFT technology is used on glass substrates to achieve light sensing properties, then light sensing capability is improved, but threshold voltage variations increase
Solution Approach 1:
The patent introduces an intermediary compensation circuit that includes a storage capacitor and switching transistors. This intermediary structure captures and stores the threshold voltage of the detection TFT at a reference time, then uses this stored value to compensate for subsequent threshold voltage variations, thereby isolating the light sensing measurement from VTH fluctuations.
Solution Approach 2:
The patent performs preliminary measurement and storage of the detection TFT's threshold voltage before the actual light sensing operation. By conducting this preliminary action and storing the VTH value in a capacitor, the system prepares compensation data in advance, allowing subsequent measurements to reference this pre-captured threshold value and maintain stability.
2Measurement precision
If CDS circuits are added to reduce VTH variations, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the CDS compensation function directly into the pixel circuit structure by integrating storage capacitors and switching transistors within each pixel unit. This merging approach combines multiple functions (detection, storage, switching, and compensation) into a unified circuit architecture, achieving signal compensation without requiring separate external compensation circuits for each pixel.
Solution Approach 2:
The detection TFT serves multiple functions: it acts as both the light sensing transistor and the switching transistor for the compensation circuit. The storage capacitor simultaneously stores both the reference voltage and the threshold voltage information. This multi-functionality reduces the total component count and circuit complexity while maintaining the CDS compensation capability.
3Adaptability or versatility
If more connections are made between pixel array and silicon IC, then signal support capability is improved, but interface size increases
Solution Approach 1:
The patent combines multiple signal processing functions (detection, amplification, CDS compensation, and signal conditioning) directly within the pixel array circuitry. By merging these functions into the pixel array itself, the patent reduces the need for extensive external signal processing circuits on the silicon IC, thereby minimizing the interface connection requirements while maintaining comprehensive signal support capability.
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 minimizes the effect of VTH variations, ensuring accurate light sensing by isolating the impact of threshold voltage fluctuations, thereby enhancing the reliability and precision of light detection.
Implementation Method 1
each of the plurality of pixel circuits including a light sensitive device and a detection TFT connected to the light sensitive device
Data Source
AI summary
A light sensing apparatus includes a pixel array including Thin Film Transistors (TFTs) and an interface integrated circuit including silicon transistors. The pixel array includes a plurality of pixel circuits. Each of the plurality of pixel circuits includes a light sensitive device and a detection TFT connected to the light sensitive device. The pixel array may also include a plurality of correlated double sampling (CDS) circuits each including a current source configured to provide current that biases a detection TFT in one of the pixel circuits to be configured as a source-follower. The interface integrated circuit includes at least one receiver circuit configured to receive an output of at least one of the CDS circuits. The CDS circuits may also include a bypass TFT, and the interface integrated circuit may also include a current source that provides current that biases a detection TFT in one of the pixel circuits to be configured as a source-follower when the bypass TFT is active.