AMOLED Pixel Driving Circuit Pre-Charge for Low Gray Brightness
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Solution Overview
Problem
Current-driven AMOLED pixels face insufficient brightness when displaying low gray scales due to delay effects from parasitic resistors and capacitors, leading to uneven image quality.
Innovation Solution
A driving circuit with a pre-charge switch is introduced, allowing the capacitor to be pre-charged by a driving power source before being charged or discharged by a current source, stabilizing the voltage and improving brightness by using different voltage levels for pre-charging and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current source is used to charge the capacitor in a current-driven AMOLED pixel, then the gray scale is determined by the current magnitude and is not affected by threshold voltage variations, but when displaying low gray scales, the small current is easily affected by parasitic resistors and capacitors causing insufficient brightness
Solution Approach 1:
The patent applies preliminary action by introducing a pre-charge switch that charges the capacitor to a threshold voltage before the current source begins charging. This preliminary charging action ensures that the capacitor starts from a known voltage state, reducing the impact of parasitic resistors and capacitors during low gray scale display, thereby solving the insufficient brightness problem while maintaining gray scale accuracy
2Device complexity
If the capacitor is charged directly by the current source without pre-charging, then the circuit is simple, but the capacitor cannot be charged within a predetermined scanning time when displaying low gray scales due to delay effects from parasitic resistors and capacitors
Solution Approach 1:
The pre-charge switch provides a preliminary charging action that prepares the capacitor before the main charging process. This preliminary action reduces the charging time by ensuring the capacitor starts from a threshold voltage state, allowing the current source to reach the required voltage level within the predetermined scanning time even when displaying low gray scales
3Device complexity
If the same voltage is used for both pre-charging and operation, then the circuit is simple, but the capacitor cannot reach the required threshold voltage level accurately, causing wrong gate voltage storage
Solution Approach 1:
The patent applies local quality by using different voltage levels for different stages of the charging process. The pre-charge switch uses a first voltage level to charge the capacitor to a threshold voltage, while the current source uses a second voltage level for the main charging process. This differentiated voltage approach ensures accurate threshold voltage storage and prevents wrong gate voltage, improving voltage precision without excessive circuit complexity
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 effectively addresses the insufficient brightness issue by ensuring the capacitor is pre-charged to a threshold voltage level, stabilizing the voltage for accurate gray-scale representation and enhancing the overall image quality.
Implementation Method 1
a current source, and the current source is used to charge/discharge a capacitor that is connected to a gate of a driving thin film transistor
Implementation Method 2
The pre-charge switch is connected to the gate of the driving thin film transistor and a driving power source, and is used for controlling the driving power source to pre-charge the capacitor
Data Source
AI summary
A method and a driving circuit for driving a current-driven active matrix organic light emitting diode (AMOLED) pixel are provided. A driving power source is used to pre-charge the capacitor before a current source charges/discharges a capacitor connected to a driving thin film transistor of the pixel. Therefore, an insufficient brightness problem during displaying a low gray can be solved.