OLED Driving Circuit Alternating Bias for Threshold Stability
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Solution Overview
Problem
Display devices using organic light-emitting diodes (OLEDs) face challenges in maintaining correct gray-scale levels due to changes in threshold voltage over time, particularly in transistors formed of amorphous silicon, which affects the reliability of light-emitting performance.
Innovation Solution
An electro-optical device with a data line driving circuit that applies alternating forward and backward bias voltages to pixel circuits, preventing threshold voltage shifts by using a data line driving circuit with forward and backward bias voltage generating circuits and a selection circuit to manage these voltages, ensuring stable gray-scale reproduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If only forward bias voltage is applied to drive the light-emitting element, then the light-emitting function is achieved, but the threshold voltage of the transistor changes over time
Solution Approach 1:
The patent applies periodic forward and backward bias voltages to the data line in alternating frame periods. During forward frame periods, forward bias voltage drives the light-emitting element to emit light. During backward frame periods, backward bias voltage is applied to suppress threshold voltage changes. This periodic alternation between light-emitting and non-light-emitting states resolves the contradiction by maintaining both illumination function and threshold voltage stability over time.
2Stability of the object's composition
If backward bias voltage is applied to suppress threshold voltage change, then threshold voltage stability is improved, but the light-emitting element does not emit light during backward frame period
Solution Approach 1:
The patent employs periodic alternation between forward frame periods (for light emission) and backward frame periods (for threshold voltage stabilization). This time-division approach allows the system to achieve both light-emitting function and threshold voltage stability by operating in different modes at different times, resolving the contradiction between illumination output and threshold voltage stability.
3Stability of the object's composition
If alternating forward and backward frame periods are applied to all pixel circuits, then threshold voltage stability is maintained, but image display is interrupted during backward frame period
Solution Approach 1:
The patent divides the pixel circuits into multiple pixel blocks and applies forward and backward frame periods to different blocks in different time slots. Some pixel blocks are in forward frame period (displaying images) while others are in backward frame period (stabilizing threshold voltage). This spatial segmentation allows simultaneous image display and threshold voltage stabilization across different regions, resolving the contradiction between image display continuity and threshold voltage stability.
Solution Approach 2:
The patent uses periodic alternation of forward and backward frame periods across different pixel blocks. Each pixel block experiences both light-emitting and non-light-emitting states periodically, but the overall display maintains continuity because different blocks are at different phases of the cycle. This resolves the contradiction by distributing the interruption across space and time.
Data Source
AI summary
An electro-optical device includes a plurality of pixel circuits each including a light-emitting element and a driving transistor for driving the light-emitting element; data lines that are connected to the plurality of pixel circuits and that supply data signals representing light-emitting gray-scale levels to the pixel circuits; and a data line driving circuit that supplies the data signals to the pixel circuits through the data lines. In addition, the data line driving circuit applies to each pixel circuit in a predetermined sequence a forward frame period supplying a data signal having a forward bias voltage for making the light-emitting element emit light and a backward frame period supplying a data signal having a backward bias voltage for making the light-emitting element not emit light, and drives each of the pixel circuits.