uLED Pixel Circuit Stabilization via Inverted Voltage Coupling

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Solution Overview

Problem

Conventional pixel circuits in micro light-emitting diode (uLED) displays are unstable due to being affected by the equivalent capacitance of the light-emitting diode, and they have a short compensation time as compensation and data writing operations are not performed simultaneously.

Innovation Solution

A pixel circuit with a 6T1C structure, including six transistors and a capacitor, where the light-emitting diode is coupled to the operating voltage instead of ground, allowing for simultaneous compensation and data writing operations, and independent LED current from equivalent capacitance, enabling internal or external compensation modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If the light-emitting diode is coupled to ground voltage in conventional configuration, then the circuit structure is simple, but the pixel circuit becomes unstable due to being affected by the equivalent capacitance of the LED

Engineering Contradiction:

Improvecircuit structureVSAvoidpixel circuit stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent inverts the conventional configuration by coupling the light-emitting diode to the operating voltage (OVDD) instead of ground voltage (OVSS). This inversion changes the reference point of the LED, making the LED current independent of the equivalent capacitance of the LED itself, thereby resolving the stability issue while maintaining circuit simplicity

Inventive Principle:

Principle #13The other way round (Inversion)

2Ease of operation

If compensation and data writing operations are performed separately in conventional pixel circuits, then the circuit operation is straightforward, but the compensation time becomes short

Engineering Contradiction:

Improveoperation simplicityVSAvoidcompensation time

Core Design Contradiction:

Ease of operationVSLoss of time

Solution Approach 1:

The patent merges the compensation operation and data writing operation into a single simultaneous process. By configuring the transistor connections and control signals appropriately, both operations occur at the same time, significantly increasing the compensation time available without complicating the operational sequence

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent performs preliminary compensation action during the data writing period. The compensation transistor is configured to enable compensation current flow during the same time period when data is being written, ensuring that compensation occurs before the light-emitting period begins, thereby extending compensation time without adding separate operation phases

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS10796631B2Pixel circuit and operating method thereof

Publication Date: 2020.10.06 AU OPTRONICS CORP

AI summary

A pixel circuit applied to an uLED display including a LED, a first transistor˜a sixth transistor and a capacitor. The LED is coupled between a first voltage and a first node. The first transistor is coupled between the first node and a second node. The second transistor is coupled between the second node and a second voltage lower than the first voltage. The third transistor is coupled between a third voltage and a third node. The fourth transistor is coupled between the third node and a fourth node. The fifth transistor is coupled between the fourth node and a fourth voltage. A terminal of the sixth transistor is coupled to the first node. The capacitor is coupled between the second node and the fourth node. The fourth transistor is controlled by a second control signal. The third transistor, the fifth transistor and the sixth transistor are controlled by a third control signal.