Double-Gate Pixel Circuit for OLED Threshold Voltage Compensation
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Solution Overview
Problem
Electroluminescent display apparatuses suffer from luminance deviations due to threshold voltage shifts in driving elements caused by process deviations and degradation, leading to degraded display quality.
Innovation Solution
An electroluminescent display apparatus with internal compensation circuits that sample and compensate for the threshold voltage of driving elements, using a double-gate driving element and reinforcement voltages to enhance sampling speed and accuracy, thereby stabilizing the driving current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional driving element is used without threshold voltage compensation, then the device complexity is low, but luminance deviation occurs due to threshold voltage shifts
Solution Approach 1:
The patent merges the threshold voltage sampling function into the existing pixel circuit by integrating a sampling capacitor and switching elements with the driving element. This combination allows threshold voltage compensation without adding a completely separate compensation circuit, thereby improving luminance consistency while controlling device complexity.
Solution Approach 2:
The patent applies preliminary action by sampling and storing the threshold voltage of the driving element in a capacitor during a dedicated sampling period before the emission period. This pre-sampled threshold voltage is then used to compensate for luminance deviations, ensuring accurate display without real-time adjustments.
2Measurement precision
If the sampling period is extended to improve threshold voltage sampling accuracy, then measurement precision improves, but the duration of the emission period is reduced
Solution Approach 1:
The patent performs threshold voltage sampling in advance during a dedicated sampling period before the emission period begins. By completing the measurement beforehand, the system ensures accurate threshold voltage capture without encroaching on the emission time, allowing both high measurement precision and sufficient emission duration.
Solution Approach 2:
The patent implements periodic action by dividing the pixel operation into distinct periods: a sampling period for threshold voltage measurement and an emission period for light output. This periodic structure allows the sampling to occur at specific intervals without continuously interfering with the emission process, maintaining both accuracy and timing.
3Measurement precision
If a sampling reinforcement voltage is applied to increase sampling current, then measurement precision improves, but use of energy increases
Solution Approach 1:
The patent applies partial action by using a sampling reinforcement voltage only during the brief sampling period when threshold voltage measurement is required, rather than continuously. This temporary voltage boost provides sufficient sampling current for accurate measurement while limiting energy consumption to only when necessary, avoiding excessive power usage during emission and other periods.
Data Source
AI summary
An electroluminescent display apparatus includes a plurality of pixels that each include a driving element including a first gate electrode connected to a first gate node, a second gate electrode facing the first gate electrode, a source electrode connected to a source node, and a drain electrode, a light emitting device connected between the source node and an input terminal for a low level driving voltage to emit light during an emission period, and an internal compensation circuit including a first capacitor connected to the first gate node and the source node. The internal compensation circuit samples a threshold voltage of the driving element during a sampling period that precedes the emission period. A sampling reinforcement voltage for increasing a sampling current flowing in the driving element is applied to the second gate electrode of the driving element during the sampling period.