Pixel Driving Circuit Threshold Compensation for OLED Mura Reduction
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Solution Overview
Problem
Existing display technologies face challenges in achieving uniform brightness and reducing display unevenness (mura) due to insufficient threshold voltage compensation, particularly in OLEDs using Low Temperature Polycrystalline Silicon (LTPS) transistors, which have high leakage currents.
Innovation Solution
A display substrate incorporating a pixel driving circuit with a compensation sub-circuit that adjusts the supply time of a signal to meet threshold conditions, combined with a reset and writing sub-circuit to ensure accurate voltage levels, and a driving sub-circuit to manage current flow, utilizing both oxide and low-temperature poly-crystalline silicon transistors to minimize leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If LTPS transistors are used in OLED display, then high reaction speed and lightness are achieved, but high leakage currents cause insufficient threshold voltage compensation and display unevenness
Solution Approach 1:
The patent introduces a threshold compensation stage that occurs before the normal display stage. During this preliminary stage, the compensation transistor adjusts the threshold voltage of the driving transistor by controlling charge transfer between capacitors, ensuring that the driving transistor has the correct threshold voltage before actual display operation begins. This preliminary action compensates for the high leakage currents inherent in LTPS transistors.
Solution Approach 2:
The patent implements a feedback mechanism where the compensation transistor continuously monitors and adjusts the threshold voltage based on the actual performance of the driving transistor. The compensation circuit uses the voltage signals from the driving transistor and storage capacitor to dynamically adjust the threshold voltage, creating a closed-loop feedback system that maintains display uniformity despite leakage currents in LTPS transistors.
2Reliability
If threshold voltage compensation is enhanced to reduce display unevenness, then brightness uniformity improves, but circuit complexity increases
Solution Approach 1:
The patent designs the compensation transistor to serve multiple functions: it acts as a switching element during the threshold compensation stage, functions as a control element for charge transfer between capacitors, and serves as part of the overall pixel driving circuit. By making the compensation transistor multi-functional, the patent reduces the need for additional dedicated components, thereby limiting the increase in circuit complexity while still achieving improved brightness uniformity.
3Measurement precision
If compensation time is extended to meet threshold conditions, then threshold voltage compensation accuracy improves, but display refresh speed decreases
Solution Approach 1:
The patent structures the threshold compensation process as a periodic action that occurs in discrete time slots within each display frame. The compensation stage is activated during specific time periods (e.g., during horizontal blanking intervals) and then stops, allowing the display to proceed to the next stage. This periodic compensation approach ensures sufficient time for accurate threshold voltage adjustment without continuously slowing down the overall display refresh rate.
Solution Approach 2:
The patent implements a multi-stage timing structure where the threshold compensation stage is completed quickly during designated time slots, and then the circuit rushes through to the next display stage. By concentrating the compensation action into specific time windows and then moving rapidly to subsequent operations, the patent achieves accurate threshold voltage compensation without significantly extending the overall display refresh period.
Data Source
AI summary
A display substrate and an operating method therefor, and a display apparatus. The display substrate comprises a plurality of pixel driving circuits and a plurality of light-emitting elements respectively connected to the plurality of pixel driving circuits, wherein the plurality of pixel driving circuits are configured to drive the plurality of light-emitting elements to emit light, and at least one pixel driving circuit comprises a first reset sub-circuit, a compensation sub-circuit, a write sub-circuit, a second reset sub-circuit, a driving sub-circuit, and a light-emission sub-circuit.