Organic EL Drive Circuit Feedback Control for Luminance Variation
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Solution Overview
Problem
Organic EL display devices experience significant luminance variation due to differences in characteristics between driver ICs, particularly in current-driven systems, leading to inconsistent drive currents and increased complexity with rising numbers of terminal pins.
Innovation Solution
An organic EL drive circuit with a first current mirror circuit and a control circuit that includes an input stage driven by a detected current and a reference current, allowing for precise control of output currents to match a reference current, eliminating the need for resistor circuits and reducing variations in drive currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of terminal pins is increased to support more display elements, then the display resolution and coverage are improved, but the variation of drive current between driver ICs increases due to characteristic differences
Solution Approach 1:
The patent implements a feedback mechanism where the output current of one driver IC is fed back to serve as the reference current for the next driver IC. This creates a closed-loop system that automatically compensates for characteristic variations between individual driver ICs, ensuring consistent drive current across all terminal pins even as the number of pins increases.
Solution Approach 2:
Each driver IC uses the output current from the previous driver IC as its own reference current, eliminating the need for external calibration or adjustment. The system self-regulates by having each component serve itself through the feedback chain, maintaining uniformity across all drivers without additional control complexity.
2Ease of operation
If conventional current drive circuits with resistor circuits are used, then the drive current can be controlled, but the manufacturing variation of resistors causes luminance variation on the screen
Solution Approach 1:
The patent removes the resistor circuits from the drive current control mechanism entirely. By extracting the resistive elements that cause manufacturing variation, the system eliminates the source of luminance inconsistency while maintaining drive current control through the feedback-based current mirror circuitry.
Solution Approach 2:
The patent replaces the passive resistor-based current control mechanism with an active feedback-controlled current mirror system. This substitution uses electronic feedback and transistor-based current mirroring instead of passive resistive division, thereby eliminating the impact of resistor manufacturing tolerances on luminance uniformity.
3Quantity of substance
If multiple driver ICs are used to drive a large number of terminal pins, then the display capacity is improved, but the difference in characteristics between driver ICs causes luminance variation
Solution Approach 1:
The patent creates a feedback chain where each driver IC's output is fed back to the next driver IC's reference input. This continuous feedback mechanism ensures that all driver ICs, regardless of their individual characteristic variations, produce consistent output currents that result in uniform luminance across the entire display.
Solution Approach 2:
The patent establishes an equipotential condition for all driver ICs by ensuring they all reference the same current level through the feedback chain. This equalizes the operating conditions for all drivers, compensating for manufacturing variations and ensuring uniform luminance output across the display surface.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces luminance variation on the screen and ensures highly precise drive currents are delivered to terminal pins, even with increased terminal pins, by controlling output currents to match a reference current, thereby improving the accuracy and consistency of drive currents across driver ICs.
Implementation Method 1
a first current mirror circuit including an input side transistor supplied with a predetermined drive current and a plurality of output side transistors for generating output currents to be distributed to a plurality of output pins provided correspondingly to terminal pins of an organic EL panel
Implementation Method 2
a control circuit including an input stage driven by the first current and a certain reference current and an output stage for generating the predetermined drive current corresponding to a difference between the first current and the certain reference current
Data Source
AI summary
A transistor for detecting current generated by an output side transistor of a current mirror circuit of an organic EL panel drive circuit and a control circuit including a current driven input stage and an output stage for driving the input side transistor of the current mirror circuit are provided. The input stage of the control circuit receives the detected current and a certain reference current and the output stage of the control circuit generates a drive current, which corresponds to a difference between the detected current and the certain reference current and drives the input side transistor of the current mirror circuit. The control circuit controls the detected current in such a manner that it becomes equal to the reference current and the current distributed to terminal pins of an organic EL panel becomes the reference current or a current corresponding thereto.