Light Sensor With Source Follower Buffer For Linear Output
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Solution Overview
Problem
Thin film transistors in display panels face challenges in providing a linear and stable output for light sensing, especially under varying light intensities and temperatures, due to unstable voltage characteristics and sensitivity to threshold voltage shifts.
Innovation Solution
A light sensor system comprising a light receiving transistor, a charging part, a signal amplifying part, and a controller that controls switching parts to maintain constant voltage between the gate and source electrodes, allowing for linear output and stability across different light conditions, including a charging switching part, reset switching part, and output switching part, with a control method that adjusts charging and discharging cycles to read output values and control display brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thin film transistor is used as a light sensor, then the display panel can sense outside light, but the output current becomes significantly variable by voltage between gate terminal and source terminal, making it difficult to obtain a linear output
Solution Approach 1:
A source follower buffer circuit is introduced as an intermediary between the light receiving transistor and the output terminal. This buffer circuit maintains a constant voltage at the source terminal, thereby stabilizing the drain current and eliminating the nonlinear output characteristics caused by voltage variations between gate and source terminals.
Solution Approach 2:
The invention changes the voltage parameter at the source terminal by introducing a voltage source that maintains constant voltage. This parameter change stabilizes the transistor operating point and ensures linear output current that is proportional to light intensity, regardless of gate-source voltage variations.
2Measurement precision
If a thin film transistor is used as a light sensor, then light sensing function is achieved, but output voltage variability increases due to threshold voltage shift from transistor deterioration
Solution Approach 1:
The source follower buffer circuit acts as a mediator that isolates the light receiving transistor from the output load. By maintaining constant voltage at the source terminal, the circuit compensates for threshold voltage shifts caused by transistor deterioration, ensuring stable output current over time.
Solution Approach 2:
The buffer circuit provides feedback by continuously monitoring and adjusting the source terminal voltage to maintain it at a constant level. This feedback mechanism compensates for threshold voltage shifts and ensures stable light sensing output despite transistor aging.
3Measurement precision
If a thin film transistor is used as a light sensor, then outside light can be sensed, but the output is affected by temperature changes
Solution Approach 1:
The source follower buffer circuit serves as a temperature-compensating intermediary by maintaining constant voltage at the source terminal. This stabilizes the transistor's operating conditions against temperature variations, reducing the harmful effect of temperature on light sensing accuracy.
Solution Approach 2:
By introducing a voltage source that maintains constant voltage at the source terminal, the invention changes the operating parameters to be independent of temperature. This ensures that the output current remains proportional to light intensity regardless of temperature changes.
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 system achieves a linear and stable output for light sensing, unaffected by changes in transistor characteristics or temperature, ensuring accurate light intensity measurement and display control across a wide range of light conditions.
Implementation Method 1
a light receiving transistor which receives outside light
Data Source
AI summary
There are provided a light sensor, a display apparatus including the same, and a control method thereof. The display apparatus includes: a display panel which includes a display area through which an image is displayed and a non-display area. A light receiving transistor which is formed in the non-display area and receives outside light. A charging part which includes a first terminal is connected to a drain electrode of the light receiving part and a second terminal is connected to a direct current voltage terminal. A signal amplifying part which includes a first terminal and a second terminal which is connected to a source of reference voltage and receives a reference voltage. A charging switching part is connected between the first input terminal and the first terminal of the charging part. A controller is provided which controls the charging switching part according to a predetermined first cycle to charge or discharge the charging part.