Matrix Photo Detection Circuits for Touch Input Coordinate Precision
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Solution Overview
Problem
Conventional display devices with integrated touch panels face issues such as increased surface reflection, necessitating additional mounting mechanisms and calibration, and require complex circuitry for accurate coordinate detection, which reduces the numerical aperture and increases the number of components in the photo sensor circuit.
Innovation Solution
A display device with a matrix array of photo detection circuits, each comprising a photo sensor, integral capacitance, and a comparator with a transistor of open drain output type, which reduces the number of components and eliminates the need for a separate coordinate arithmetic circuit by using X and Y output lines to detect optical currents in multiple gray scales.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photo detection means is constituted of photo sensor, buffer TFT, output selection TFT, and reset TFT, then photo detection function is achieved, but circuit scale is increased and numerical aperture of display part is lowered
Solution Approach 1:
The patent merges the buffer amplifier function into the pixel circuit structure itself, eliminating the need for separate buffer amplifier circuits. The photo sensor output is directly connected to the pixel electrode through shared circuit elements, integrating multiple functions into a single circuit unit and reducing overall circuit scale.
Solution Approach 2:
The pixel circuit is designed to serve dual purposes: displaying image data and detecting touch coordinates through the photo sensor. The same TFT and capacitance elements used for display also function as part of the photo detection circuit, making the circuit multi-functional and reducing the need for separate dedicated components.
2Reliability
If buffer amplifier is used to output photo sensor signal, then signal output is achieved, but numerical aperture of display part is lowered
Solution Approach 1:
The buffer amplifier function is merged into the pixel circuit structure, eliminating separate buffer amplifier components that would block light paths. The photo sensor signal is output directly through the pixel electrode and shared circuit elements, maintaining light transmission and preserving numerical aperture.
3Measurement precision
If means to binarize analog voltage on peripheral circuit is provided, then coordinate detection is achieved, but transistor with high function is necessary increasing circuit complexity
Solution Approach 1:
The pixel circuit itself performs the binarization function through its inherent switching characteristics. The TFT acts as a threshold device that automatically converts analog photo sensor output into digital states based on the applied voltage levels, eliminating the need for separate binarization circuits.
Solution Approach 2:
The patent replaces complex peripheral binarization circuits with the inherent switching property of the TFT within the pixel circuit. The transistor's on/off states naturally provide the binarized output, substituting mechanical/peripheral processing with integrated electronic switching.
4Measurement precision
If coordinate arithmetic means is provided to specify coordinates based on detected two-dimensional image, then coordinate specification is achieved, but device complexity is increased
Solution Approach 1:
The display device itself performs coordinate detection through the integrated photo sensor array without requiring external coordinate arithmetic means. The pixel circuit and photo sensor work together to directly determine touch coordinates based on light blockage patterns.
Solution Approach 2:
The display device serves dual functions: displaying images and detecting touch coordinates. The same pixel array and photo sensors used for visual display also function as the coordinate detection system, eliminating the need for separate coordinate arithmetic hardware.
5Adaptability or versatility
If touch panel is mounted on display panel, then touch function is achieved, but visibility is deteriorated due to increase of surface reflection
Solution Approach 1:
The touch detection function is merged with the display structure itself, eliminating the need for separate touch panel layers. The photo sensors are integrated within the display panel structure, allowing touch detection without additional surface mountings that would cause reflection.
Solution Approach 2:
The patent extracts the touch detection function from the traditional separate touch panel and integrates it directly into the display pixel circuit. This removes the need for additional touch panel layers and their associated reflective surfaces, improving visibility.
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 solution allows for accurate detection of input coordinates without additional coordinate arithmetic circuits, reducing the complexity of the photo sensor circuit and maintaining the numerical aperture of the display part, thereby integrating touch panel functionality without compromising image quality.
Implementation Method 1
a photo sensor which converts an incident light into an optical current corresponding to intensity of the incident light
Data Source
AI summary
A display device with a touch pad function is provided which reduces the elements required to form a photo sensor while still accurately detecting input coordinate positions. The display device includes a display part on which a plurality of pixels are arranged in a matrix array, a plurality of photo detection circuits which are arranged in a matrix array in the inside of the display part, wherein each photo detection circuit of the plurality of photo detection circuits includes: a photo sensor which converts an incident light into a optical current corresponding to intensity of the incident light, an integral capacitance which integrates the optical current converted by the photo sensor, and a comparator to which a voltage of the integral capacitance is inputted, and the comparator includes a transistor of an open drain output type with a grounded source.