Pixel Driving Circuit Anode Reset for SAR Overshoot Control

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Solution Overview

Problem

Existing electroluminescent display devices face challenges in accurately controlling light emission, leading to image quality issues due to overshoot in shooting amount ratio (SAR) when image patterns change.

Innovation Solution

A display device with a pixel driving circuit that includes a light emitting element, a driving TFT, a switching unit, and an anode reset unit, which applies specific voltages and reset signals to ensure accurate grayscale expression and reduce SAR overshoot.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a conventional pixel driving circuit is used, then the device structure is simple, but SAR overshoot occurs causing inaccurate grayscale expression and poor image quality

Engineering Contradiction:

Improvegrayscale expression accuracyVSAvoidpixel driving circuit structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The pixel driving circuit is segmented into multiple functional units: a driving TFT for current control, a switching unit with multiple switching TFTs for voltage selection, and an anode reset unit with reset TFTs for voltage stabilization. This segmentation allows each unit to perform its specific function independently, improving grayscale accuracy while managing complexity through modular design.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The anode reset unit applies a reset voltage to the anode of the light emitting element before the driving voltage is applied. This preliminary action stabilizes the anode voltage and prevents SAR overshoot when the image pattern changes, ensuring accurate grayscale expression from the start of each frame.

Inventive Principle:

Principle #10Preliminary action

2Stability of the object's composition

If the anode voltage is not reset, then the circuit operation is continuous, but SAR overshoot occurs when image patterns change causing luminance instability

Engineering Contradiction:

Improveanode voltage stabilityVSAvoidreset operation timing

Core Design Contradiction:

Stability of the object's compositionVSLoss of time

Solution Approach 1:

The anode reset unit operates periodically at specific timing points during each frame cycle. Reset TFTs are turned on at predetermined timing to apply reset voltage to the anode, stabilizing it before new driving voltages are applied. This periodic reset action prevents SAR overshoot while maintaining continuous display operation.

Inventive Principle:

Principle #19Periodic action

3Measurement precision

If multiple switching TFTs and reset TFTs are added, then voltage control precision is improved, but the number of transistor components increases

Engineering Contradiction:

Improvevoltage control precisionVSAvoidnumber of transistor components

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The switching unit uses multiple switching TFTs that can selectively apply different voltages (first voltage for sensing, second voltage for driving) to the gate electrode of the driving TFT. The anode reset unit uses reset TFTs that can apply reset voltage at different timing points. These multi-functional components improve voltage control precision while managing the increase in transistor count through efficient resource utilization.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS20250157383A1Display Device and Method of Driving Same

Publication Date: 2025.05.15 LG DISPLAY CO LTD

AI summary

A display device includes a light emitting element including an anode to which driving power is input and a cathode to which a low power is applied, a driving TFT including a first electrode to which high power is input, a second electrode to which the driving power is applied, and a gate electrode, a switching unit configured to apply a first voltage for sensing characteristics of the driving TFT or a second voltage for driving the driving TFT when an on-level scan signal is input, and an anode reset unit configured to apply an anode reset voltage to the anode of the light emitting element in association with the switching unit.