Micro-LED Pixel Circuit Precharge Transistor Response Speed
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Solution Overview
Problem
Micro-LED display devices experience low response speed and luminance output at low gray-scales due to short current flow times and voltage charging times, which are inherent to the pulse width modulation (PWM) scheme used for gray-scale control.
Innovation Solution
A micro-LED pixel circuit that biases the anode electrode with a precharge voltage before emission, improving response speed and minimizing luminance decrease by stabilizing current flow during low gray-scale operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PWM scheme is used to control gray-scale by adjusting current flow time, then gray-scale control is achieved, but response speed decreases and luminance output decreases at low gray-scales
Solution Approach 1:
The patent applies preliminary action by charging the anode electrode voltage to a higher level before the emission period begins. The precharge transistor activates during a precharge period prior to emission, preparing the anode voltage in advance. This preliminary voltage preparation ensures that when the emission signal activates at low gray-scales, the micro-LED can immediately respond without waiting for voltage charging, thereby resolving the response speed issue while maintaining PWM gray-scale control.
2Ease of operation
If PWM scheme is used to control gray-scale by adjusting current flow time, then gray-scale control is achieved, but luminance output decreases at low gray-scales
Solution Approach 1:
The precharge transistor charges the anode electrode to a higher voltage level before the emission period starts. This preliminary voltage elevation ensures that when emission occurs at low gray-scales with short current flow times, the micro-LED receives sufficient voltage to produce adequate luminance output, preventing the luminance decrease problem while preserving PWM-based gray-scale control capability.
3Speed
If voltage charging time is extended to improve response speed, then response speed improves, but emission time is reduced due to PWM constraints
Solution Approach 1:
The patent separates the voltage charging function from the emission function by introducing a precharge period distinct from the emission period. During the precharge period, the precharge transistor charges the anode voltage in advance. During the subsequent emission period, the emission transistor activates current flow. This temporal separation allows voltage charging to occur beforehand without consuming emission time, enabling fast response while maintaining adequate emission duration for light output.
Solution Approach 2:
The patent segments the operation into distinct phases: a precharge period for voltage preparation and an emission period for light output. The precharge transistor operates during the precharge period to elevate anode voltage, while the emission transistor operates during the emission period to drive current through the micro-LED. This segmentation allows each function to occur in its optimal time window without compromising the other, resolving the conflict between response speed and emission time.
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 precharge voltage biasing technique enhances response speed and reduces luminance decrease at low gray-scales, while also improving performance in high gray-scale operations by ensuring stable current application and immediate light emission.
Implementation Method 1
a precharge transistor configured to bias an anode electrode of the micro-LED with a precharge voltage in response to a precharge signal
Implementation Method 2
a micro-LED configured to emit light based on a magnitude of a current flowing in the current path
Data Source
AI summary
A micro-LED pixel circuit includes a driving transistor configured to generate a current path; an emission transistor configured to be turned on in response to an emission signal to generate the current path with the driving transistor; a micro-LED configured to emit light based on a magnitude of a current flowing in the current path; and a precharge transistor configured to bias an anode electrode of the micro-LED with a precharge voltage in response to a precharge signal, wherein the precharge signal is enabled before the emission signal is enabled, thereby biasing an anode electrode of a micro-LED with a precharge voltage before emission in a PWM operation of the micro-LED, and improving a response speed of the micro-LED and minimizing luminance decrease at the low gray-scale.