Reset Compensation Circuit for AMOLED Threshold Voltage Uniformity
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Solution Overview
Problem
Existing low-temperature polysilicon processes for AMOLED panels suffer from poor uniformity of threshold voltages in driving transistors, leading to non-uniform brightness of OLEDs due to different driving currents generated by transistors with varying threshold voltages.
Innovation Solution
A pixel circuit with a data writing circuit, a reset compensation circuit, a light emission control circuit, and a driving transistor, where the reset compensation circuit connects nodes to perform threshold voltage compensation, allowing for the generation of a light emission voltage (V0 = 2*V1 + Vth - Vdata) that compensates for the threshold voltage of the driving transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-temperature polysilicon process is used for AMOLED panel manufacturing, then manufacturing cost and process complexity are reduced, but uniformity of threshold voltages of driving transistors deteriorates
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the light emission phase. The reset compensation circuit calculates and stores the threshold voltage of the driving transistor in advance (during reset and compensation phases), then uses this pre-calculated value to generate the light emission voltage. This preliminary calculation eliminates the need for real-time adjustments during light emission, ensuring uniformity while maintaining process simplicity.
Solution Approach 2:
The patent introduces an intermediary element - the reset compensation circuit - that acts as a mediator between the data writing circuit and the light emission control. This circuit calculates the threshold voltage, generates the light emission voltage with compensation, and stores it in the storage node. The intermediary circuit decouples the manufacturing simplicity from the precision requirement, allowing the polysilicon process to remain simple while achieving uniform threshold voltage compensation.
2Illumination intensity
If threshold voltage compensation is implemented, then OLED brightness uniformity is improved, but circuit structure complexity increases
Solution Approach 1:
The patent merges the reset function and threshold compensation function into a single reset compensation circuit. The same circuit that resets the gate voltage of the driving transistor also calculates and stores the threshold voltage. This merging eliminates the need for separate compensation circuits, reducing overall circuit complexity while achieving brightness uniformity through threshold voltage compensation.
Solution Approach 2:
The reset compensation circuit performs multiple functions: it resets the gate voltage, calculates the threshold voltage of the driving transistor, generates the compensated light emission voltage, and stores it for use during light emission. This multi-functional design achieves brightness uniformity without adding dedicated compensation circuitry, thereby limiting the increase in circuit complexity.
3Measurement precision
If light emission voltage is generated using formula V0=2*V1+Vth−Vdata, then compensation precision is improved, but calculation complexity and time increase
Solution Approach 1:
The patent performs the complex voltage calculation in advance during the reset and compensation phases, before the light emission phase begins. The reset compensation circuit calculates V0 = 2*V1 + Vth - Vdata and stores the result in the storage node. This preliminary calculation ensures high precision compensation while minimizing the time impact on the actual light emission, as the calculation is completed beforehand.
Solution Approach 2:
The patent replaces real-time mechanical/electrical adjustment during light emission with a pre-calculated voltage storage system. Instead of dynamically adjusting voltages during the light emission phase, the system calculates and stores the precise compensated voltage in advance, then simply retrieves it during light emission. This substitution reduces calculation time during critical phases while maintaining precision.
Data Source
AI summary
A method of driving a display device, where the display device includes a display substrate including a plurality of rows of pixel circuits, and in each pixel circuit, a reset compensation circuit and a data writing circuit are connected at a second node, and the reset compensation circuit is connected to a reset control signal line and a first voltage input terminal; in a driving stage, driving a light emitting device OLED connected to each of other rows of pixel circuits except a last row of pixel circuits further includes a charge maintenance stage performed after a light emission voltage generation stage; and in the stable display stage, all light emitting devices OLED simultaneously emit light; where in the charge maintenance stage, the first voltage input terminal is disconnected from the second node by the reset compensation circuit in response to control of a reset control signal.