Pixel Repair Circuit With Capacitance Compensation for OLED Displays
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Solution Overview
Problem
Display devices suffer from yield deterioration due to transistor defects in pixel circuits, leading to parasitic capacitance issues in repair lines that cause incorrect lighting of repaired pixels, especially at low grayscale levels, and affect adjacent normal pixels.
Innovation Solution
The display device incorporates a specific transistor configuration and capacitors to manage parasitic capacitance, including a storage capacitor, hold capacitor, and compensation capacitor, along with a repair line connected to a bad pixel, to ensure accurate lighting of repaired pixels based on data signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a repair line is used to connect transistors and anode electrode of a bad pixel, then the light emitting element of the repaired pixel can emit light, but parasitic capacitance is formed in the repair line causing the light emitting element to not emit light at low grayscale levels or to erroneously emit light
Solution Approach 1:
The harmful parasitic capacitance effect is extracted and compensated by introducing a compensation capacitor connected to the repair line. This separate compensation element isolates the harmful effect from the repair line itself while providing a means to counteract it through controlled charging and discharging operations.
Solution Approach 2:
The parasitic capacitance, which initially causes harmful effects (dark spots at low grayscale, erroneous light emission), is converted into a beneficial element by using it as a compensation target. The compensation capacitor is specifically designed to counterbalance the parasitic capacitance, transforming the problem into a solution where the harmful capacitance becomes part of the compensation mechanism.
2Reliability
If transistors of a repair pixel are connected to an anode electrode of a light emitting element of a bad pixel using a repair line, then the bad pixel can be repaired, but voltage of the repair line changes affecting adjacent normal pixels
Solution Approach 1:
The compensation capacitor acts as an intermediary element between the repair line and the rest of the circuit. It mediates the voltage fluctuations by absorbing or supplying charge as needed, preventing direct transmission of voltage changes to adjacent normal pixels while maintaining the repair functionality.
Solution Approach 2:
The compensation capacitor is pre-charged to a specific voltage level before repair operations begin. This beforehand cushioning of charge provides a buffer that absorbs subsequent voltage fluctuations, preventing them from propagating to adjacent pixels and causing erroneous light emission.
3Reliability
If parasitic capacitance is formed between the repair line and anode electrodes of light emitting elements of normal pixels, then the light emitting element of the repaired pixel may erroneously emit light, but adding compensation components increases device complexity
Solution Approach 1:
The compensation capacitor serves multiple functions: it compensates for parasitic capacitance effects, stabilizes voltage on the repair line, prevents erroneous light emission in both repaired and adjacent normal pixels, and maintains compatibility with existing pixel circuit operations. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The compensation capacitor is integrated into the existing pixel circuit structure, merging the repair functionality with the display operation. The compensation mechanism is combined with the normal pixel driving circuitry, allowing both functions to operate simultaneously without requiring completely separate systems.
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 allows the repaired pixel to emit light correctly corresponding to the data signal, minimizing dark spots and voltage fluctuations, thereby improving display quality and yield.
Implementation Method 1
a storage capacitor connected between the first node and the second node
Implementation Method 2
a light emitting element of a bad pixel, which is connected between a second end of the repair line and a second power source
Data Source
AI summary
A display device includes: a display panel including a display area including pixels and a non-display area including a dummy pixel; a scan driver which supplies a scan signal to the display panel; a data driver which supplies a data signal to the display panel; and a timing controller which supplies a first control signal for controlling the scan driver and a second control signal for controlling the data driver. The dummy pixel is connected to a bad pixel among the pixels in the display area through a repair line, and a connection of the dummy pixel to the repair line is cut off in an initialization phase in which a voltage of an initialization power source is supplied.