Light Detecting TFT Circuit for Screen Input
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Solution Overview
Problem
Conventional image display units with optical sensors for screen input functions require numerous thin-film transistors per pixel, leading to a decrease in numerical aperture and increased power consumption, which reduces screen brightness and operating time, especially in portable devices.
Innovation Solution
The design incorporates a light detecting TFT connected in series with a switching TFT, sharing electrodes and capacitors, with a sensor control line and storage capacitor to accumulate and read photoelectric current, reducing the number of additional components and maintaining high illuminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an optical sensor comprising many thin-film transistors is provided for each pixel, then the screen input function is achieved, but the numerical aperture of pixel decreases and power consumption increases
Solution Approach 1:
The patent combines the optical sensor function with the existing pixel circuit by integrating a light detecting TFT and switching TFT into a unified circuit structure. The light detecting TFT shares its drain electrode with the switching TFT's source electrode, and the storage capacitor serves dual purposes for both display and sensor operations, thereby achieving screen input function without proportionally increasing component count
Solution Approach 2:
The storage capacitor in the pixel circuit is designed to serve multiple functions: it stores charge for display operations and simultaneously accumulates photoelectric current for touch sensing. The switching TFT also serves dual roles in display switching and sensor signal routing, making the pixel circuit multi-functional and reducing the need for separate dedicated sensor components
2Adaptability or versatility
If an optical sensor with multiple thin-film transistors is integrated into each pixel, then screen input function is achieved, but power consumption increases reducing operating time
Solution Approach 1:
By merging the optical sensor circuit with the existing pixel circuit structure, the patent eliminates the need for separate power supply paths and control circuits that would otherwise be required. The shared storage capacitor and electrode connections reduce the total number of active components that consume power, thereby extending operating time while maintaining screen input functionality
Solution Approach 2:
The patent employs periodic scanning of sensor control lines to readout photoelectric current from multiple pixels sequentially. This periodic action allows the sensor to operate in a time-division manner, reducing the simultaneous active component count and lowering peak power consumption while maintaining full screen input capability
3Adaptability or versatility
If an optical sensor with many elements is provided for each pixel, then screen input function is achieved, but the brightness of the screen is deteriorated
Solution Approach 1:
The patent merges the optical sensor components within the existing pixel aperture boundaries rather than adding separate external sensor elements. The light detecting TFT and switching TFT share the same pixel electrode and storage capacitor infrastructure, ensuring that the light-receiving area remains maximized while achieving screen input function, thus preserving screen brightness
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 configuration suppresses the decrease in numerical aperture and power consumption associated with optical sensor integration, enabling efficient screen input without compromising display brightness or operating time.
Implementation Method 1
a second thin-film transistor connected in series to the first thin-film transistor and receiving projection of said light
Data Source
AI summary
An image display unit with screen input function is provided, by which it is possible to input image data directly to a screen without decreasing numerical aperture of pixel. The image display unit comprises a light detecting TFT 61 receiving a light entering from a screen of a liquid crystal display panel, said light detecting TFT 61 is connected in series to a switching TFT 60, which does not receive a light entering from the screen of the liquid crystal display panel. To a source electrode of the light detecting TFT 61, a storage capacitor Cst and a pixel electrode of a liquid crystal element are connected. The liquid crystal element is represented by a capacitor CLC. A sensor control line 140 is connected to the gate electrode of the light detecting TFT 61, and a gate line 120 is connected to the gate electrode of the switching TFT 60. A data line 110 is connected to the drain electrode of the switching TFT 60, and a storage line 150 is connected to one end of a storage capacitor Cst. An image signal is sent to a pixel electrode (ITO) of the liquid crystal element (CLC). The light detecting TFT 61 transmits photoelectric current Isig generated by sensing the light to a sensor signal processing circuit (see FIG. 1) via the data line 110.