Pixel Driving Circuit Threshold Voltage Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electroluminescent display devices face challenges in maintaining image quality due to power consumption issues, brightness non-uniformity, and the difficulty in accurately compensating for threshold voltage of driving transistors, especially at high resolutions and variable frequencies, leading to defects like spots, afterimages, and cross-talk.
Innovation Solution
A pixel driving circuit design that includes a driving transistor, capacitors, and switching circuits to secure sufficient compensation time for threshold voltage sensing, reducing leakage current and brightness variations by implementing NMOS transistors and PMOS transistors, and adjusting voltages to maintain consistent light emission across frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the horizontal scanning period is reduced to increase resolution and driving frequency, then the display quality and refresh rate are improved, but the sensing time for threshold voltage compensation becomes insufficient
Solution Approach 1:
The patent performs threshold voltage sensing operations in advance during previous horizontal scanning periods (e.g., (n-2)H time before the nth horizontal scanning period). By preparing the compensation data beforehand and storing it in the pixel circuit, the system ensures that sufficient sensing time is allocated without compromising the current frame's display timing, thus resolving the conflict between high driving frequency and adequate sensing time.
2Ease of manufacture
If p-type polycrystalline transistors are used in the pixel driving circuit, then the device can be manufactured with standard processes, but leakage current is generated at the gate node during low-speed driving
Solution Approach 1:
The patent changes the electrical parameters of the transistor by switching between different transistor types (p-type and n-type) depending on the driving mode. During normal-speed driving, p-type transistors are used for standard manufacturing. During low-speed driving, the circuit switches to use n-type transistors which have lower leakage current characteristics, thus adapting the device parameters to match the operating conditions and eliminate leakage issues.
3Speed
If the sensing time is not secured for more than one horizontal scanning period in high-speed driving, then the circuit operates within timing constraints, but image quality defects such as spots, afterimages, and cross-talk occur
Solution Approach 1:
The patent divides the threshold voltage sensing operation into multiple discrete time slots across different horizontal scanning periods. Instead of attempting to complete all sensing operations within a single scanning period, the process is segmented into sequential steps performed at (n-2)H, (n-1)H, and nth periods, with intermediate storage in pixel circuit capacitors. This segmentation allows adequate time for each sensing operation while maintaining high overall driving speed and preventing image defects.
Data Source
AI summary
A pixel driving circuit in each of the pixels includes: a first switching circuit that turned on in response to the (n-2) th scan signal to provide a V1 voltage to a first node, provide a V3 voltage to a third node, and provide a V2 voltage to an anode of the light-emitting element; a second switching circuit turned on in response to the nth scan signal to electrically connect the first node to a second node, provide a V5 voltage to the third node, and provide a data voltage to a fourth node; and an emission control circuit turned on in response to the nth emission signal to electrically connect a second node to the anode and provide a reference voltage to the fourth node.