Active Matrix Display Storage Capacitor Discharge Control
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Solution Overview
Problem
Existing active matrix electroluminescent display devices face challenges in maintaining consistent light output due to differential aging of light-emitting diodes, particularly at lower grey levels, where optical feedback systems are less effective and result in lower average light intensity and increased errors.
Innovation Solution
The introduction of a light-dependent device that controls the discharge of a storage capacitor, combined with additional circuit elements such as inverters and feedback transistors, to increase the rate of capacitor discharge and improve the switching off of the drive transistor, ensuring consistent correction across all grey levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light-dependent device is used to control discharge of the storage capacitor for correcting differential aging, then correction effectiveness is improved, but the discharge rate is too slow at lower grey levels resulting in lower average light intensity and increased errors
Solution Approach 1:
The patent applies dynamics by making the discharge rate adaptive rather than fixed. The circuit dynamically adjusts the discharge characteristics based on the operating conditions, allowing fast discharge when needed (at lower grey levels) and controlled discharge when correction is the priority (at higher grey levels), thereby resolving the contradiction between correction precision and discharge speed
Solution Approach 2:
The patent changes the electrical parameters of the discharge circuit by introducing additional transistors that modify the discharge path and resistance. This allows the system to transition between different discharge rates, enabling both precise correction and sufficiently fast discharge to maintain acceptable average light intensity across all grey levels
2Measurement precision
If the storage capacitor discharges slowly to maintain correction accuracy, then measurement precision is improved, but productivity decreases due to lower average light intensity and longer response time
Solution Approach 1:
The system dynamically balances correction accuracy and light output by using control transistors that adjust the discharge characteristics in real-time. This allows the capacitor to discharge at different rates depending on the required correction, maintaining both accuracy and acceptable productivity
Solution Approach 2:
The patent modifies circuit parameters by adding transistors that create alternative discharge paths, effectively changing the time constant and discharge rate. This enables the system to achieve both precise aging correction and sufficient average light intensity by optimizing the discharge parameters
3Speed
If additional circuit elements are added to increase capacitor discharge rate, then speed is improved, but device complexity increases
Solution Approach 1:
The additional transistors in the circuit serve multiple functions: they control the discharge rate, provide gain amplification, and enable the overall correction mechanism. By making these components multi-functional, the patent minimizes the number of additional elements needed, thereby limiting the increase in device complexity while achieving the desired speed improvement
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 enhances the correction for differential aging, providing improved performance at all grey levels by accelerating the discharge of the storage capacitor, thereby reducing light errors and maintaining consistent brightness.
Implementation Method 1
a light-dependent device for controlling discharge of the storage capacitor, thereby to alter the control of the drive transistor in dependence on the light output of the display element
Data Source
AI summary
An active matrix EL display device has pixels comprising an EL display element, a drive transistor and a storage capacitor for storing a voltage to be used for controlling the addressing of the drive transistor. Each pixel also has a light-dependent device for controlling discharge of the storage capacitor, thereby to alter the control of the drive transistor in dependence on the light output of the display element. A circuit is associated with the drive transistor for increasing the rate of discharge of the storage capacitor when the storage capacitor is discharged in response to the light dependent device output. This improvement in the rate of capacitor discharge ensures that good correction for differential aging is obtained at all grey levels.