Light-Emitting Pixel Circuit With Boosting Capacitor for Ghost Reduction
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Solution Overview
Problem
Display devices experience luminance differences and distortion phenomena due to leakage currents and hysteresis characteristics of driving transistors, especially at low driving frequencies, leading to ghost images and reduced display quality.
Innovation Solution
Incorporation of a boosting capacitor connected to the gate electrode of the driving transistor and an initialization transistor, along with specific transistor configurations and timing control of scan and emission signals, to manage bias voltage application and minimize ghost phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bias voltage is supplied to the driving transistor during the blank period to maintain its on-state, then the transistor remains conductive and ready for the next frame, but a ghost phenomenon occurs where patterns from the lower portion appear as afterimages at the upper portion of the display panel
Solution Approach 1:
The patent applies preliminary action by initializing the anode electrode of the light emitting element before the bias voltage is applied to the driving transistor during the blank period. The initialization transistor supplies an initialization voltage to the anode electrode, clearing any residual charge that would otherwise cause the ghost phenomenon. This preliminary initialization action prevents the harmful effect while maintaining the transistor's on-state stability.
2Use of energy by moving object
If the display device operates at a low driving frequency, then power consumption is reduced, but luminance differences occur between the active period and blank period due to leakage current and hysteresis characteristics
Solution Approach 1:
The patent applies periodic action by supplying the initialization voltage to the anode electrode at regular intervals during each blank period, synchronized with the frame frequency. This periodic initialization ensures that any charge accumulation from leakage current or hysteresis effects is continuously cleared, maintaining uniform luminance across frames while allowing the display to operate at low driving frequencies for reduced power consumption.
3Area of stationary object
If the number of scan lines is reduced to increase the area ratio of active emission lines, then the display area is more efficiently utilized, but the resolution and image quality deteriorate
Solution Approach 1:
The patent applies parameter changes by optimizing the initialization voltage level and timing parameters to compensate for the reduced number of scan lines. By adjusting these electrical parameters, the display maintains adequate resolution and image quality even with fewer scan lines, allowing the active emission area ratio to increase while minimizing the deterioration of display precision.
Data Source
AI summary
A pixel may include: a light emitting element; a first transistor connected between a first node electrically connected to a first driving power source and a second node electrically connected to an anode electrode of the light emitting element, the first transistor to control a driving current; a second transistor connected between a data line and the first node; a third transistor connected between the second node and a third node connected to a gate of the first transistor; a fourth transistor connected between the third node and a first initialization power source; a fifth transistor connected between a second initialization power source and the anode electrode of the light emitting element, the fifth transistor being turned on by a scan signal provided to a scan line; and a boosting capacitor connected between the scan line and the third node.