OLED Drive TFT Precharge Circuit for Gray Scale Uniformity
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Solution Overview
Problem
Existing organic EL display apparatuses face irregularities in gray scale display due to variations in threshold voltage of OLED drive TFTs, leading to non-uniform light emission and potential residual images, especially under low power supply conditions or high accuracy conditions with insufficient reset time.
Innovation Solution
Applying a pre-charge signal to set the initial voltage potential of the OLED drive TFT gate to a fixed value prior to reset, ensuring the OLED drive TFT can be reset in a short time with no variations, using a pre-charge TFT switch to maintain a fixed voltage potential during the reset operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a reset TFT switch is used to compensate for threshold voltage variations in OLED drive TFTs, then gray scale display uniformity is improved, but device complexity increases due to additional switching elements and control circuits
Solution Approach 1:
The patent applies preliminary action by introducing a pre-charge TFT switch that sets the gate voltage of the OLED drive TFT to a predetermined value before the reset operation. This pre-charging step ensures that the gate voltage starts from a known state, enabling accurate reset and compensation of threshold voltage variations without requiring complex additional circuits. The pre-charge switch works in conjunction with the reset switch to achieve uniform gray scale display while maintaining relatively simple device structure.
2Manufacturing precision
If reset time is extended to ensure complete voltage convergence, then threshold voltage variation compensation is improved, but response time increases leading to slower display updating
Solution Approach 1:
The pre-charge TFT switch performs preliminary voltage setting before the reset operation, ensuring the gate voltage starts from a predetermined value. This eliminates the need for extended reset time to reach a known state, allowing the reset to complete quickly while still achieving accurate threshold voltage compensation. The pre-action reduces the effective reset duration needed.
Solution Approach 2:
The patent changes the parameter of gate voltage initialization by using the pre-charge switch to set the gate voltage to a predetermined value before reset. This parameter change enables the reset operation to be both fast and accurate, as the voltage convergence starts from a controlled initial state rather than an undefined previous state, resolving the trade-off between reset time and compensation accuracy.
3Device complexity
If the initial gate voltage potential is left undefined from previous frame, then device complexity is reduced, but gray scale display uniformity deteriorates due to variations in threshold voltage
Solution Approach 1:
The pre-charge TFT switch performs a preliminary action by setting the gate voltage to a predetermined value before the reset operation. This ensures that even though the initial voltage from the previous frame is undefined and varies, the gate voltage is standardized to a known value during the pre-charge phase. Subsequent reset operation then accurately compensates for threshold voltage variations, achieving uniform gray scale display without requiring complex additional circuits.
Data Source
AI summary
In organic EL display apparatuses, when the reset operating time required for compensating variations in the OLED drive TFT voltage threshold is too short then fluctuations in the threshold voltage Vth cannot be corrected and an accurate gray scale is impossible. A precharge voltage is supplied from the precharge TFT switch prior to the reset TFT switch and the light TFT switch resetting the Vth of the OLED driver TFT, in order to apply a specified voltage value to the gate voltage of the OLED driver TFT prior to reset. The voltage potential on the gate of the OLED driver TFT prior to reset is therefore no longer an undetermined voltage potential so variations in the gate voltage after reset are suppressed and variations in the gray scale are suppressed.