TFT Driving Voltage Compensation for Display Ghosting
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Solution Overview
Problem
Thin film transistor liquid crystal display (TFT-LCD) devices face issues with ghosting and flickering due to long-term voltage differences causing I-V characteristic drift, leading to changes in drain current and leakage rates in the display area.
Innovation Solution
A driving voltage compensating method and circuit that uses a reference TFT to simulate the voltages of TFTs in the display area, obtaining a compensation voltage value based on the driving current drift, and adjusting the gate-on and gate-off voltages to compensate for the voltage differences, thereby stabilizing the driving voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TFTs in the display area operate under long-term voltage difference between gate and source/drain, then the display device can maintain normal display function, but the I-V characteristic of TFT drifts causing drain current to change and producing ghosting and flicker
Solution Approach 1:
The patent applies preliminary action by measuring the driving current of the reference TFT and obtaining compensation voltage values before the display operation. The compensation voltage is calculated in advance based on the measured driving current and stored in a lookup table, so that when display operation begins, the compensation can be immediately applied to counteract the voltage drift effects, preventing ghosting and flicker before they occur
Solution Approach 2:
The patent implements feedback by using the measured driving current of the reference TFT to generate compensation voltage values that are then applied to adjust the gate voltages of TFTs in the display area. This creates a closed-loop system where the actual performance (driving current) is measured and used to correct the operating conditions (gate voltage), thereby stabilizing the I-V characteristics and eliminating drift-induced display defects
2Reliability
If a reference TFT is added to detect driving current and provide compensation, then the I-V characteristic drift can be compensated and display quality improved, but the device structure and complexity increase
Solution Approach 1:
The patent applies copying by using a reference TFT that replicates the electrical characteristics and operating conditions of the TFTs in the display area. This reference copy is placed in a dummy region and subjected to the same voltage conditions, allowing its driving current to serve as a representative indicator of the entire display array's state, thereby enabling indirect monitoring and compensation without adding complexity to each pixel
Solution Approach 2:
The patent uses an intermediary approach by introducing a compensation circuit that includes a lookup table and control logic. This intermediary system measures the driving current, translates it into compensation voltage values through the lookup table, and applies the corrected voltages to the display TFTs. This mediator layer simplifies the overall system by centralizing the compensation function rather than requiring complex compensation mechanisms in each pixel
Data Source
AI summary
A driving voltage compensating method and a driving voltage compensating circuit for a display device are provided. The compensating method includes: providing a reference TFT; obtaining a driving current of the reference TFT; acquiring a compensation voltage value according to the driving current; and compensating a driving voltage for TFTs in a display area according to the compensation voltage value. By setting the reference TFT to obtain a drift behavior of I-V characteristic curve of the TFTs in the display area, obtaining the compensation voltage value according to a driving current drift value and compensating the driving voltage for the TFTs in the display area, the problem(s) of ghost and/or flicker in the display device caused by the drift of I-V characteristic curve resulting from a long-term voltage difference can be solved consequently.