Pixel Circuit Brightness Modulation via Time Length Control
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Solution Overview
Problem
Conventional brightness control methods for LEDs, such as pulse width modulation (PWM) and amplitude modulation, face challenges in maintaining high external quantum efficiency (EQE) and resolution, leading to excessive current flow and design difficulties in display panels.
Innovation Solution
The implementation of a pixel circuit with a driving transistor and a light-emitting time length modulator, which receives pulse width and amplitude control signals to modulate the time length of driving signals provided to the light-emitting device, allowing for uniform high brightness modulation while maintaining high EQE and reducing the total current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If amplitude modulation is used for brightness control, then the LED can operate with sufficient driving current, but the high external quantum efficiency (EQE) cannot be effectively maintained
Solution Approach 1:
The patent employs pulse width modulation (PWM) technique where the LED is driven by periodic pulse signals with varying duty cycles. The LED operates at full current during the on-period to maintain high EQE, and remains off during the off-period. By adjusting the duty cycle (ratio of on-time to total period), the perceived brightness is controlled while the LED always operates at optimal efficiency points when conducting current.
2Loss of energy
If pulse width modulation (PWM) is used for brightness control, then the external quantum efficiency can be maintained, but design difficulties arise in response to requirements for high resolution
Solution Approach 1:
The patent divides the pixel circuit into multiple functional modules: a driving transistor for current control, a light-emitting time length modulator for PWM control, and a control switch for timing. This segmentation allows each module to perform its specific function efficiently, simplifying the overall control architecture while achieving high-resolution brightness control through the modulator's ability to precisely adjust pulse width.
Solution Approach 2:
The light-emitting time length modulator acts as an intermediary component between the control signal and the LED. It receives control signals and translates them into precise pulse width modulation, serving as a buffer that simplifies the control interface while enabling fine-grained brightness control for high-resolution displays.
3Loss of energy
If the LED operates with sufficient driving current to maintain high EQE, then the brightness can be controlled, but the total amount of current flowing through the display panel becomes excessive
Solution Approach 1:
The patent uses PWM to drive the LED in periodic on-off cycles. During the on-period, the LED receives full driving current to maintain high EQE. During the off-period, current flow is zero. By adjusting the duty cycle, the average current over time is reduced while the peak current during on-periods remains at the optimal level for efficiency, thus solving the contradiction between maintaining high EQE and reducing total current consumption.
Data Source
AI summary
A display panel and a pixel circuit of the display panel are provided. The pixel circuit includes a driving transistor and a light-emitting time length modulator. The driving transistor has a control terminal receiving a pulse width control signal and an amplitude control signal, and the driving transistor generates a driving signal. In a first time period, the light-emitting time length modulator modulates a time length of a plurality of second time periods for providing the driving signal to a light-emitting device according to a light-emitting time control signal.