Display Apparatus with Threshold-Voltage Correction Circuit
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Solution Overview
Problem
Active-matrix display apparatuses using organic EL devices face issues with non-uniform luminance due to variations in the threshold voltage and mobility of driving transistors, leading to changes in light emission over time.
Innovation Solution
Incorporating a switching transistor and threshold-voltage correction means to perform threshold-voltage and mobility correction operations during a non-luminous period, ensuring consistent light emission by stabilizing the voltage across the driving transistor's terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a driving transistor is used to control the light emitting device, then the light emitting device can be driven with low power consumption, but non-uniform luminance occurs due to variations in threshold voltage and mobility
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage correction before the actual light emission period. A correction operation is conducted in advance using a correction signal to adjust the gate voltage of the driving transistor, compensating for threshold voltage variations before the luminance is generated. This ensures uniform luminance across different pixels while maintaining low power consumption during the actual display operation.
2Stability of the object's composition
If the driving transistor operates in saturation region, then the drain current is stable, but the anode voltage changes over time causing luminance variation
Solution Approach 1:
The patent implements feedback by monitoring the actual luminance output and adjusting the gate voltage accordingly. The feedback signal is generated based on the difference between the actual luminance and the target luminance, and this feedback signal is used to correct the gate voltage of the driving transistor. This closed-loop control compensates for voltage changes over time and maintains stable luminance while preserving the saturation region operation for current stability.
3Manufacturing precision
If threshold voltage correction operation is performed continuously, then luminance uniformity is maintained, but the light emitting device cannot emit light during correction period
Solution Approach 1:
The patent applies periodic action by conducting threshold voltage correction operations at specific intervals rather than continuously. The correction operation is performed periodically during non-luminous periods or in alternating time slots, allowing the light emitting device to emit light during other periods. This periodic correction maintains luminance uniformity across different pixels while ensuring sufficient light emission duration.
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
The solution achieves uniform luminance by canceling variations in threshold voltage and mobility, maintaining constant current flow to the light emitting device, regardless of changes in the driving transistor's characteristics.
Implementation Method 1
The organic EL device is a device using a phenomenon in which an organic thin film emits light when an electric field is impressed on the film
Data Source
AI summary
A display apparatus includes: a pixel array section including a row of first and second scanning lines, a column of signal lines, and pixels in a matrix, each of the pixels disposed at an intersection of both of the lines; and a drive section. The drive section performs line progressive scanning on the pixels. The pixel includes a light emitting device, a sampling transistor, a driving transistor, a switching transistor, and a holding capacitor. The sampling transistor samples a video signal on the signal line to hold the signal potential in the holding capacitor, the driving transistor makes the light emitting device conductive to be in a luminous state in accordance with the held signal potential, and the switching transistor becomes ON in accordance with the control signal supplied in advance of the sampling of the video signal to change the light emitting device to a non-luminous state.