OLED Pixel Circuit Dual-Stage Initialization for High Resolution
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Solution Overview
Problem
High-resolution and high-driving-frequency organic light emitting diode (OLED) display devices face challenges in storing data voltage due to short gate on time, leading to insufficient charging of storage capacitors and reduced luminance.
Innovation Solution
The implementation of a pixel structure with a storage capacitor, a first switching transistor, a driving transistor, and a second switching transistor, which performs a first reset operation using a first initialization voltage and a second reset operation using a second initialization voltage, lower than the first, to maintain a constant current path direction and ensure sufficient charging rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the resolution or driving frequency of the display panel is increased, then the display quality and responsiveness are improved, but the gate on time becomes shorter, leading to insufficient charging of the storage capacitor
Solution Approach 1:
The patent applies preliminary action by performing a reset operation in the previous horizontal time (before the current data writing period) to prepare the storage capacitor for efficient charging. The reset transistor is turned on during a reset period to initialize the voltage at the first node, ensuring that when the data writing period begins, the capacitor is ready to charge quickly with the available gate on time. This advance preparation resolves the contradiction by making effective use of the limited charging time in high-resolution, high-frequency displays.
2Productivity
If the gate on time is shortened, then the display can achieve higher resolution and driving frequency, but the charging rate of the storage capacitor becomes insufficient, resulting in reduced luminance
Solution Approach 1:
The patent applies parameter changes by dynamically controlling the voltage levels during different periods. Specifically, during the reset period, the voltage at the second node is set to a first voltage level, and during the data writing period, it is changed to a second voltage level. This voltage parameter change optimizes the charging characteristics of the storage capacitor, enabling sufficient charging current to be achieved within the shortened gate on time, thereby maintaining luminance despite higher resolution and driving frequency.
Solution Approach 2:
By performing the reset operation in advance during the previous horizontal time, the patent ensures that the storage capacitor starts its charging process from an optimized initial state. This preliminary action maximizes the utilization of the limited gate on time, allowing the capacitor to charge adequately even when the time window is reduced due to high resolution and driving frequency requirements, thus preserving luminance output.
3Device complexity
If a single initialization voltage is used, then the circuit design is simpler, but the charging rate and current path consistency are insufficient
Solution Approach 1:
The patent applies segmentation by dividing the initialization process into two distinct voltage stages: a first voltage level during the reset period and a second voltage level during the data writing period. This segmentation of the voltage parameter allows for optimized charging characteristics at different stages of operation, ensuring consistent current path direction and reliable charging rate, while the overall structure remains integrated within the existing pixel circuit framework.
Data Source
AI summary
A display device includes a switch, an initialization line, a capacitor, a data line, a first transistor, a second transistor, a driving transistor, and a diode. The capacitor includes a first electrode and a second electrode. To the first electrode through at least the initialization line, the switch may output a first voltage in a first period of a horizontal time and may output a second voltage unequal to the first voltage in a second period of the horizontal time. The first transistor may connect the data line to the first electrode in response to a scan signal. The driving transistor may provide a driving current based on a voltage of the first electrode. The second transistor may connect the initialization line to the second electrode in response to an initialization signal. The diode may emit light based on the driving current.