Organic EL Pixel Circuit Threshold Voltage Stabilization
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Solution Overview
Problem
In organic EL display apparatuses, variations in threshold voltage of drive transistors across pixels lead to luminance unevenness, which existing threshold-voltage correction functions struggle to compensate for, especially over time, resulting in increased power consumption due to higher operating voltages.
Innovation Solution
The implementation of a pixel circuit configuration that includes a write scanner and signal selector to apply a predetermined reference potential, optimizing the bias state of drive transistors to minimize threshold voltage variations by balancing forward and reverse biases during light emission and no-light emission periods, thereby reducing the need for high power-supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple matrix driving method is used, then the structure is simple, but it is difficult to implement large size and high definition
Solution Approach 1:
The patent divides the pixel circuit into multiple functional components: sampling transistor, signal holding capacitor, drive transistor, and light emitting device. This segmentation allows each component to perform a specific function, enabling active matrix driving capability while maintaining manageable circuit complexity for large-scale integration in high-definition displays
2Manufacturing precision
If threshold-voltage correction function is strengthened to compensate for variations, then luminance uniformity improves, but power consumption increases due to higher operating voltages
Solution Approach 1:
The signal holding capacitor holds the video signal voltage before the drive transistor operates, preparing the control voltage in advance. This preliminary action allows the drive transistor to operate with stable gate voltage, reducing threshold voltage variations and enabling lower operating voltages while maintaining luminance uniformity across pixels
Solution Approach 2:
The patent implements a feedback mechanism where the signal holding capacitor maintains the video signal voltage level, and the drive transistor adjusts its output based on this held voltage. This feedback loop compensates for threshold voltage variations without requiring increased operating voltages, thus reducing power consumption while improving luminance uniformity
3Manufacturing precision
If higher power-supply voltages are applied to compensate for threshold voltage variations, then luminance uniformity improves, but power consumption increases
Solution Approach 1:
The patent changes the parameter of gate voltage control by using the signal holding capacitor to maintain stable voltage levels. Instead of increasing power-supply voltage to compensate for threshold variations, the system modifies the gate voltage parameter through precise holding and control, achieving luminance uniformity with lower overall power consumption
Data Source
AI summary
An image display apparatus includes a pixel array section and a drive section configured to drive the pixel array section. The pixel array section is a pixel-circuit matrix with pixel circuits each serving as a matrix element. The drive section has at least a write scanner for supplying the control signal to each of the scan lines in order to carry out a sequential scanning operation on the scan lines for every field and a signal selector for supplying a video signal to each of the signal lines with a timing adjusted to the sequential scanning operation. Each of the pixel circuits employs at least a sampling transistor, a drive transistor, a signal holding capacitor and a light emitting device.