TFT Optical Sensor Readout for Wide Dynamic Range Without Saturation
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Solution Overview
Problem
Conventional TFT optical sensor systems face limitations in dynamic range and signal-to-noise ratio, particularly when sensing low light levels, due to noise issues in 1-transistor pixel architectures and reduced pixel density in 3-transistor architectures.
Innovation Solution
The implementation of a thin-film transistor (TFT) optical sensor system with a charge amplifier, analog-to-digital converter, accumulator, and controller circuit that allows for extended read cycles and reset of charge amplifiers based on voltage or digitized values, enhancing dynamic range by accumulating charge over multiple sub-read cycles without saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a 1-transistor pixel architecture is used, then the pixel density (PPI) is maximized, but the noise level increases and dynamic range is reduced
Solution Approach 1:
The patent divides the pixel architecture into two distinct parts: a 1-transistor photo diode for charge collection and a separate charge amplifier for signal processing. This segmentation allows the pixel to maintain high density while the external charge amplifier provides low-noise amplification, thus improving signal-to-noise ratio without sacrificing pixel density.
2Reliability
If a 3-transistor pixel architecture is used, then the signal-to-noise ratio is improved, but the pixel density is reduced
Solution Approach 1:
The patent extracts the charge amplifier function from within the pixel structure and places it externally. This removes the additional transistors from the pixel, allowing higher pixel density while maintaining the low-noise amplification benefits that would otherwise require extra transistors within the pixel.
3Productivity
If the charge amplifier integration time is extended, then the dynamic range is increased, but the charge amplifier saturates at high light levels
Solution Approach 1:
The patent implements periodic resetting of the charge amplifier during the integration period. Instead of continuous integration that leads to saturation, the charge amplifier is reset at regular intervals, allowing it to maintain a linear response across a wider dynamic range while still capturing total light accumulation over the extended period.
Solution Approach 2:
The patent uses feedback control to monitor the charge amplifier output and trigger resets when saturation is approaching. This feedback mechanism ensures the charge amplifier operates within its linear range while still allowing extended integration times for increased dynamic range measurement.
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 approach increases the effective dynamic range by allowing more charge information to be collected from each pixel, maintaining a linear response and avoiding saturation, thereby improving the system's ability to handle low light levels without noise degradation.
Implementation Method 1
Each TFT pixel on the sensor may collect charge proportional to an amount of incident light
Data Source
AI summary
An optical sensor system includes a thin-film transistor (TFT) optical panel including an array of TFT pixels, a charge amplifier configured to temporarily store a charge received from a TFT pixel in the array of TFT pixels and generate a voltage based on the temporarily stored charge, an analog-to-digital converter to generate a digitized value based on the voltage, an accumulator configured to store the digitized value, and a controller circuit configured to cause the temporarily stored charge in the charge amplifier to be reset based on one of the voltage and the digitized value.