Scan Driver Stage Circuit for Stable N-Type Transistor Turn-Off
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Solution Overview
Problem
In organic light emitting displays, N-type transistors used in scan drivers face issues with stable turn-off due to threshold voltage shifts, leading to erroneous operations, and existing methods for concurrent or progressive scan signal supply are not reliable.
Innovation Solution
A stage circuit design that includes a progressive driver and a concurrent driver, utilizing specific transistor configurations and capacitor arrangements to ensure transistors are turned off with lower gate voltages than source voltages, allowing for stable and reliable concurrent or progressive scan signal supply to scan lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If N-type transistors are used in scan drivers to reduce manufacturing cost by concurrent formation with pixels, then manufacturing cost is reduced, but transistor turn-off stability deteriorates due to threshold voltage shifts
Solution Approach 1:
The patent changes the voltage parameter applied to the gate electrode, specifically applying a negative voltage relative to the source electrode to ensure the transistor is turned off. This parameter change compensates for threshold voltage shifts that occur over time, maintaining reliable transistor turn-off while using N-type transistors formed concurrently with pixels in the display panel.
2Device complexity
If conventional transistor gating is used where gate voltage equals source voltage, then device simplicity is maintained, but transistor turn-off control deteriorates due to threshold voltage shifts over time
Solution Approach 1:
The patent modifies the gate voltage parameter from being equal to source voltage to being negatively offset relative to source voltage. This simple parameter change ensures that even when threshold voltage shifts occur over time, the transistor remains reliably turned off when intended, without requiring complex control circuits.
3Speed
If scan signals are supplied concurrently to all scan lines, then display refresh speed is improved, but signal control complexity increases
Solution Approach 1:
The patent segments the scan driver into multiple independent stage circuits, each controlling a specific scan line. Each stage circuit can be independently controlled to supply scan signals concurrently or progressively, allowing flexible control of signal supply timing while achieving fast display refresh through concurrent operation when needed.
Solution Approach 2:
The patent enables dynamic control of scan signal supply timing by allowing each stage circuit to operate in different modes (concurrent or progressive) based on control signals. This dynamic flexibility allows the system to optimize between speed and control complexity depending on the operating conditions.
Data Source
AI summary
A stage circuit is capable of concurrently or progressively supplying scan signals. The stage circuit includes a progressive driver including a first transistor and a second transistor, and a concurrent driver including an 11th transistor and a 12th transistor. When the first transistor, the second transistor, the 11th transistor, and the 12th transistor are turned off, lower voltages than voltages applied to source electrodes are applied to gate electrodes such that the transistors can be stably turned off.