Image Pickup Device Source Follower Circuit Half Tone Accuracy
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Solution Overview
Problem
Existing image-pickup devices with integrated display functions using low-temperature polysilicon technology face challenges in accurately representing half tones due to signal attenuation from parasitic capacitances, requiring complex processes for image-pickup conditions.
Innovation Solution
An image-pickup device incorporating a photoelectric conversion element, a storage capacitor, and an amplifying thin-film transistor forming a source follower circuit, allowing for analog output and improved representation of half tones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-temperature polysilicon technique is used for image-pickup devices with integrated display functions, then manufacturing ease is improved, but measurement precision deteriorates due to signal attenuation from parasitic capacitances
Solution Approach 1:
The patent introduces a storage capacitor as an intermediary element between the photoelectric conversion element and the output circuit. This capacitor temporarily holds the electric charge generated by light irradiation, preventing signal attenuation caused by parasitic capacitances in the low-temperature polysilicon TFT circuitry. The storage capacitor acts as a buffer that maintains signal integrity while allowing the use of easier-to-manufacture low-temperature polysilicon technology.
2Reliability
If binary digital values are used for output, then noise tolerance is improved, but manufacturing precision deteriorates due to difficulty in representing half tones
Solution Approach 1:
The patent employs a dynamic output mechanism where the image-pickup device can switch between binary digital output mode and analog output mode. The output circuit is designed to provide analog voltage levels corresponding to the amount of stored electric charge, enabling precise representation of half tones and grayscale values. This dynamic capability allows the system to adapt to different application requirements, providing both noise tolerance of digital systems and precision of analog representation when needed.
3Measurement precision
If amplification function using SRAM is implemented, then signal attenuation is reduced, but device complexity increases
Solution Approach 1:
The patent extracts the essential amplification and signal holding function from complex SRAM-based circuits and implements it using a simpler capacitor-based storage mechanism. By separating the signal storage function (performed by the capacitor) from the readout function (performed by the output circuit), the design achieves signal amplification and attenuation prevention without requiring complex SRAM circuits. This extraction of core functionality reduces device complexity while maintaining signal accuracy.
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
Enables increased speed and gradation of image-pickup processing, suitable for touch panels and liquid-crystal display applications, with reduced aperture ratio and enhanced multipoint recognition.
Implementation Method 1
a photoelectric conversion element that converts light into electric charge
Data Source
AI summary
An image-pickup device includes a photoelectric conversion element 5 that converts light into electric charge, a capacitor 6 that stores electric charge which the photoelectric conversion element 5 has obtained by conversion, reset means 7 for discharging the electric charge in the capacitor 6, and an amplifying thin-film transistor 8 that receives, amplifies, and outputs the electric charge stored in the capacitor 6. In addition, the image-pickup device is configured so that the amplifying thin-film transistor 8 forms a source follower circuit.