Inorganic LED Pixel Driver Circuit for Luminance Uniformity
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Solution Overview
Problem
Inorganic light-emitting diode (LED) display devices experience luminance deviations and image quality deterioration due to the variation in light wavelength with driving current, unlike organic LEDs, which control luminance by adjusting the driving current.
Innovation Solution
A display device design incorporating a first pixel driver and a second pixel driver, with transistors and capacitors to generate and control control currents and driving currents, respectively, to minimize luminance deviations by managing the amplitude and duty distribution of the control current applied to inorganic LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If inorganic LEDs are driven by adjusting driving current to control luminance, then luminance control is achieved, but luminance deviations and image quality deterioration occur due to wavelength variation with driving current
Solution Approach 1:
The patent changes the control parameter from driving current magnitude to driving current period (pulse width modulation). Instead of varying current amplitude to control luminance, the invention maintains constant current amplitude and varies the time duration of current pulses, which prevents wavelength variation while achieving luminance control.
Solution Approach 2:
The invention introduces dynamic control of the driving current period through a pixel driver that adjusts the pulse width based on grayscale information. The period of the driving current is dynamically varied to control luminance output, replacing static current amplitude control with dynamic time-based control.
2Illumination intensity
If driving current is varied to control luminance in inorganic LEDs, then luminance adjustment is possible, but threshold voltage distribution of transistors varies causing luminance deviations
Solution Approach 1:
The patent changes the control parameter from driving current amplitude to driving current period. By using pulse width modulation instead of amplitude modulation, the invention eliminates the coupling between current magnitude and transistor threshold voltage variations, achieving uniform luminance control across pixels with different transistor characteristics.
Solution Approach 2:
The pixel driver circuit acts as an intermediary that converts grayscale voltage information into controlled driving current periods. This intermediary processing stage decouples the relationship between input signal and actual LED current, compensating for transistor threshold voltage variations through the period control mechanism.
Data Source
AI summary
A display device includes: a first pixel driver to generate a control current; a second pixel driver to generate a driving current, and control a period during which the driving current flows, based on the control current; and a light-emitting element connected to the second pixel driver to receive the driving current. The first pixel driver includes: a first transistor to generate the control current based on a first data voltage; and a second transistor to provide the first data voltage to a first electrode of the first transistor based on a scan write signal from a scan write line. The second pixel driver includes: a third transistor to generate the driving current based on the control current; and a fourth transistor to provide a second data voltage to a first electrode of the third transistor based on a scan write signal from the scan write line.