Light Sensing Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The light sensing type touch panel faces challenges due to low current values from photodiodes, which result in reduced accuracy in touch determination and location due to variations in threshold voltages of driving transistors caused by fabrication and manufacturing variables.
Innovation Solution
A light sensing circuit that includes a photodiode, a driving transistor, a capacitor, and switching transistors to amplify the current and compensate for threshold voltage deviations, using PMOS transistors and shared signal lines with pixel driving circuits to improve sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thin film transistors are used to amplify current in light sensor circuits, then the current amplification function is achieved, but threshold voltage variations due to fabrication variables cause reduced touch determination accuracy
Solution Approach 1:
The patent applies preliminary action by storing the threshold voltage value of each driving transistor in a dedicated storage unit during a threshold voltage measurement period before normal operation. This pre-measured threshold voltage information is then used to compensate for variations during touch detection, eliminating the need for real-time threshold voltage measurement and improving touch determination accuracy despite manufacturing variations.
2Measurement precision
If photodiode area is increased to generate more current, then sensitivity improves, but the thickness of the touch panel increases
Solution Approach 1:
The patent changes the operational parameters of the photodiode by applying optimized voltages during light integration periods and using pulse-driven operation modes. This allows the photodiode to generate sufficient current signals for accurate touch detection without requiring an increased physical area, thereby maintaining thin panel thickness while improving detection sensitivity through electrical parameter optimization rather than geometric expansion.
3Adaptability or versatility
If separate layers are added for light sensing functionality, then touch detection capability is enhanced, but the device complexity and thickness increase
Solution Approach 1:
The patent implements multi-functionality by integrating the light sensing function directly into the existing pixel circuit structure. The pixel circuit serves dual purposes: displaying visual information and detecting touch events through integrated photodiodes. This eliminates the need for separate dedicated light sensing layers, reducing overall device complexity while maintaining enhanced touch detection capability through the unified circuit design.
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 enhances the sensitivity and accuracy of touch detection by amplifying the current generated by the photodiode and compensating for threshold voltage variations, leading to more precise touch location determination.
Implementation Method 1
a photodiode including a cathode electrode and an anode electrode and for receiving light from the outside and generating a current corresponding to the received light
Data Source
AI summary
A light sensing circuit includes a photodiode including a cathode electrode and an anode electrode and for receiving light from the outside and generating a current corresponding to the received light, a driving transistor for amplifying the current generated in the photodiode, a capacitor for storing a first initiation voltage transmitted to the driving transistor, a first switching transistor for compensating for a threshold voltage of the driving transistor corresponding to a current scan signal, and a second switching transistor for transmitting the first initiation voltage corresponding to the current scan signal.