OLED Pixel Circuit Error Compensation for Brightness Uniformity
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Solution Overview
Problem
In OLED display manufacturing, uneven threshold voltages in transistors lead to inconsistent display brightness and reduced quality due to errors in voltage at the node P during the charging and light-emitting phases, causing variations in current flow through the light-emitting component.
Innovation Solution
A pixel circuit is designed with an error compensation unit connected to the voltage storage terminal of the charging unit, which adjusts the voltage at the node P using a light-emitting control signal to mitigate voltage errors, and optionally includes a voltage buffer unit to stabilize voltage variations, ensuring consistent brightness and improved display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pixel circuit is used without error compensation, then the circuit structure is simple, but voltage errors at node P cause uneven display brightness and reduced display quality
Solution Approach 1:
The patent introduces an error compensation unit as an intermediary component between the charging unit and light-emitting unit. This unit includes a compensation transistor (M6) and compensation capacitor (C6) that act as mediators to detect and correct voltage errors at node P, thereby improving display brightness uniformity without fundamentally changing the core pixel circuit structure
Solution Approach 2:
The pixel circuit is segmented into distinct functional units: charging unit (M1-M5, C1-C3), light-emitting unit (M1-M3, OLED), and error compensation unit (M6, C6). Each unit operates independently with specific functions, allowing the error compensation mechanism to be added without redesigning the entire circuit, thus managing complexity through modular segmentation
2Reliability
If the charging unit stores voltage without compensation, then the circuit operation is simple, but channel charge injection from transistor M3 introduces voltage error ΔV1 that affects light-emitting current consistency
Solution Approach 1:
The error compensation unit performs preliminary anti-action by pre-compensating for the voltage error ΔV1 that will be introduced by channel charge injection from transistor M3. The compensation transistor M6 is activated during the charging phase to inject compensating charge into node P, counteracting the harmful voltage error before it affects the light-emitting current consistency
Solution Approach 2:
The compensation capacitor C6 provides feedback by storing the compensating charge and maintaining the corrected voltage at node P throughout the light-emitting phase. This feedback mechanism ensures that the voltage error is continuously compensated, improving current consistency without requiring complex real-time control circuits
Data Source
AI summary
A pixel circuit and a display device. The pixel circuit includes a charging unit, a light-emitting unit and an error compensation unit; a voltage storage terminal of the charging unit is connected to a voltage input terminal of the light-emitting unit; one end of the error compensation unit is connected to the voltage storage terminal of the charging unit, a voltage at the voltage storage terminal of the charging unit is used to determine a magnitude of a current flowing through the light-emitting unit; a control terminal of the error compensation unit is configured to receive a light-emitting control signal which is used to control the light-emitting unit to emit light or stop emitting light, the error compensation unit is configured to lower the voltage at the voltage storage terminal of the charging unit when the light-emitting control signal controls the light-emitting unit to emit light.