Compact Pixel Circuit Using Global Lines for Luminance Accuracy
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Solution Overview
Problem
Conventional pixel circuits with a source follower structure face limitations in achieving high PPI and high resolution due to insufficient threshold voltage compensation and parasitic capacitor variations, leading to inaccurate luminance and inefficient operation.
Innovation Solution
A pixel circuit design with reduced transistors and capacitors, utilizing a first global signal line for compensation and a second global signal line for initialization, allowing simultaneous signal reception and eliminating the need for additional scan drivers, thereby increasing integration density and improving luminance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a source follower structure is included in the pixel circuit to compensate for threshold voltage shift, then threshold voltage compensation is improved, but the pixel circuit area increases and integration density decreases
Solution Approach 1:
The patent extracts and eliminates the source follower structure from the pixel circuit, retaining only the essential components (driving transistor, compensation transistor, holding capacitor) while achieving threshold voltage compensation through alternative means, thereby reducing the pixel circuit area and increasing integration density
Solution Approach 2:
The compensation transistor serves multiple functions: it compensates for threshold voltage shifts, maintains node voltage stability, and enables accurate luminance emission, replacing the need for separate source follower components while achieving the same reliability goals
2Reliability
If a source follower structure is included in the pixel circuit, then threshold voltage compensation is improved, but the operating time required for compensation increases
Solution Approach 1:
The patent performs preliminary threshold voltage compensation during the initialization period before the light emitting element needs to emit light at the target luminance. The compensation transistor adjusts the threshold voltage of the driving transistor in advance, ensuring that when the light emitting element operates, the threshold voltage is already compensated, thereby eliminating the need for additional compensation time during the emission period
Solution Approach 2:
The compensation process is integrated into the initialization sequence and continues seamlessly into the emission period without interruption. The compensation transistor remains active throughout, ensuring continuous threshold voltage maintenance while the light emitting element emits light at the target luminance, eliminating dead time between compensation and emission
3Reliability
If conventional pixel circuit structure is used, then threshold voltage compensation can be achieved, but the PPI and resolution are limited due to insufficient integration density
Solution Approach 1:
The patent removes unnecessary components (source follower structure, additional capacitors) from the conventional pixel circuit, retaining only the essential elements needed for threshold voltage compensation and light emission, thereby significantly reducing the pixel circuit area and enabling high PPI and resolution displays
Solution Approach 2:
The patent merges the compensation function and the light emission function into a unified pixel circuit structure where the compensation transistor and holding capacitor work together with the driving transistor to achieve both threshold voltage compensation and accurate luminance emission without requiring separate functional blocks, thereby increasing integration density
Data Source
AI summary
A pixel circuit may include a first transistor including a control electrode connected to a first node, a first electrode receiving a first power supply voltage, and a second electrode connected to a second node, a second transistor including a control electrode receiving a writing gate signal, a first electrode receiving a data voltage, and a second electrode connected to a third node, a third transistor including a control electrode receiving a compensation gate signal, a first electrode connected to the first node, and a second electrode connected to the second node, a fourth transistor including a control electrode receiving an initialization gate signal, a first electrode connected to the second node, and a second electrode receiving an initialization voltage, a holding capacitor including a first electrode connected to the third node and a second electrode connected to the first node, and a light emitting element.