OLED Pixel Circuit Current Path Stabilization
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Solution Overview
Problem
In OLED displays, the reduced size of pixels leads to decreased storage capacitor capacity, causing voltage fluctuations at the terminals of the storage capacitor due to logic level transitions and noise, resulting in unstable luminance during one frame.
Innovation Solution
The OLED display incorporates a pixel circuit with a storage capacitor, a driving transistor, a switching transistor, and a current path circuit, where the switching transistor is turned off in response to a rising edge, and the current path circuit applies charges stored in the second node to maintain stable voltages at the terminals of the storage capacitor, using a current path transistor and anode initialization transistors to ensure constant voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is decreased to increase resolution, then the display resolution is improved, but the storage capacitor capacity is reduced causing voltage fluctuations and unstable luminance
Solution Approach 1:
The patent introduces a current path circuit as an intermediary component between the storage capacitor and the rest of the pixel circuit. This circuit includes a current path transistor that provides a dedicated charge discharge path, preventing voltage fluctuations at the storage capacitor terminals caused by transistor off-currents and logic level transitions, thereby maintaining stable luminance despite reduced capacitor capacity.
Solution Approach 2:
The patent modifies the electrical parameters of the pixel circuit by adding the current path circuit that controls charge flow. This changes the voltage stability parameter of the storage capacitor, ensuring that the voltage at both terminals remains constant even when the capacitor capacity is reduced due to smaller pixel size.
2Area of stationary object
If the storage capacitor capacity is reduced due to smaller pixel size, then the pixel area is decreased improving resolution, but the voltage at capacitor terminals becomes unstable due to noise and logic transitions
Solution Approach 1:
The current path circuit serves as an intermediary that mediates between the reduced-capacity storage capacitor and the variable current demands of the pixel circuit. By providing a controlled charge discharge path through the current path transistor, it stabilizes the voltage at the capacitor terminals despite the smaller capacitor size.
Solution Approach 2:
The current path circuit is designed to preemptively handle voltage fluctuations by providing a dedicated charge discharge path before instability can affect the luminance. The circuit compensates for anticipated voltage variations caused by transistor off-currents and logic level transitions, cushioning the storage capacitor voltage from these disturbances.
3Ease of operation
If transistor off-current and logic level transitions occur, then normal circuit operation is enabled, but significant voltage changes occur at storage capacitor terminals affecting luminance stability
Solution Approach 1:
The current path transistor acts as an intermediary that isolates the storage capacitor from the effects of transistor off-currents and logic level transitions. It provides a controlled path for charge discharge that prevents these normal operational variations from causing significant voltage changes at the capacitor terminals, thereby maintaining luminance stability.
Solution Approach 2:
The current path circuit implements a feedback mechanism where the voltage at the storage capacitor terminals is monitored and adjusted through the current path transistor. When voltage fluctuations occur due to transistor off-current or logic transitions, the feedback mechanism activates to restore the voltage to its stable level, ensuring consistent luminance output.
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 configuration maintains stable voltages at the terminals of the storage capacitor, ensuring constant luminance of the OLED during one frame, thereby improving image quality by reducing voltage fluctuations and maintaining consistent light emission.
Implementation Method 1
An OLED pixel circuit includes the OLED, a driving transistor to control, based on a voltage between a gate and a source, a current supplied to the OLED
Implementation Method 2
a storage capacitor electrically connected to the first node and configured to maintain a constant voltage at the first node
Data Source
AI summary
An organic light-emitting diode (OLED) display is disclosed. In one aspect, the display includes a driving transistor having a gate electrode electrically connected to a first node and configured to supply a driving current to an OLED based on a voltage of the gate electrode. A storage capacitor electrically connects to the first node and is configured to maintain a constant voltage at the first node. A switching transistor electrically connects to the first node and includes a pair of transistors that are configured to be simultaneously turned on based on a first control signal. The transistors are serially connected to each other via a second node, and a current path circuit electrically connects to the second node and is configured to receive a charge stored in a capacitance of the second node when the switching transistor is turned off.