Display Device Threshold Voltage Correction Circuit
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Solution Overview
Problem
Current active matrix type flat panel emissive display devices face challenges in achieving high precision due to variations in threshold voltages and mobilities of transistors, which affect emission luminance and image quality, and require complex pixel circuits for correction.
Innovation Solution
A simplified pixel circuit and driving method that includes a pixel array unit with row scan lines, column signal lines, and power supply lines, utilizing a sampling transistor, driver transistor, and holding capacitor to perform video signal sampling and correction, while reducing the number of constituent elements and layout area, thereby correcting for transistor and organic EL device variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a correction function is added to control emission luminance uniformly, then luminance uniformity is improved, but pixel circuit complexity increases
Solution Approach 1:
The patent merges the correction function into the existing pixel circuit by utilizing the driver transistor's inherent characteristics and the holding capacitor's voltage storage capability. The correction period is integrated into the normal driving cycle, allowing threshold voltage correction without adding separate correction circuits or transistors. This combines the correction function with the existing pixel structure, achieving luminance uniformity while avoiding increased circuit complexity.
Solution Approach 2:
The driver transistor serves multiple functions: it acts as both the primary drive transistor for controlling light emission and as a correction transistor for threshold voltage compensation. The holding capacitor similarly serves dual purposes by maintaining the drive voltage and storing correction voltage. This multi-functionality allows the pixel circuit to perform correction operations without requiring additional dedicated components.
2Measurement precision
If more constituent elements are added to achieve correction function, then correction precision is improved, but layout area increases
Solution Approach 1:
The patent combines the correction function with existing pixel components rather than adding separate correction circuits. The driver transistor and holding capacitor, which are already necessary for basic pixel operation, are utilized to perform threshold voltage correction. This merging approach maintains correction precision while avoiding additional layout area consumption.
Solution Approach 2:
The pixel circuit performs self-correction using its own internal components. The driver transistor's threshold voltage is corrected by utilizing the voltage stored in the holding capacitor during a correction period, without requiring external correction circuits or additional transistors. This self-service mechanism achieves precise correction while minimizing area overhead.
3Measurement precision
If control signal pulse width is reduced to correct mobility variation, then mobility correction precision is improved, but susceptibility to transmission delay increases
Solution Approach 1:
The patent applies correction voltage to the holding capacitor before the main sampling operation during a correction period. This preliminary correction establishes the proper threshold voltage baseline before the actual video signal is sampled and stored. By performing the correction action in advance, the system achieves accurate mobility compensation while maintaining sufficient time margins against transmission delays.
Solution Approach 2:
The correction operation is implemented as a periodic action within each frame or field cycle. A specific correction period is allocated during which the holding capacitor is charged to a voltage that compensates for mobility variations. This periodic correction approach maintains precision while allowing the system to tolerate transmission delays by ensuring the correction is established before sampling begins.
Data Source
AI summary
A display device includes pixel array unit and a driver unit. A sampling transistor samples a signal potential to hold the signal potential in a holding capacitor. A driver transistor flows a drive current to a light emitting element in accordance with the signal potential held. A main scanner in the driver unit outputs the control signal having a shorter pulse width than the time period to the scan line to make the sampling transistor conductive during a time period while the signal line is at the signal potential, thereby adding the signal potential a correction for a mobility of the driver transistor when the signal potential is held in the holding capacitor.