Real-Time Threshold Voltage Sensing for Driving TFT in OLED Displays
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Solution Overview
Problem
Conventional methods for sensing the threshold voltage of driving TFTs in organic light emitting displays are not capable of real-time operation due to the long time required for the gate-source voltage to reach the threshold voltage, leading to luminance differences between pixels.
Innovation Solution
A device and method that applies a first and second data voltage to the gate node of the driving TFT during specific programming and sensing periods, calculating a sensing ratio to determine the change in threshold voltage, allowing for real-time sensing during vertical blanking intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gate-source voltage is allowed to reach saturation state by conventional source follower method, then the threshold voltage sensing is accurate, but the sensing time becomes too long for real-time operation
Solution Approach 1:
The patent applies preliminary action by pre-charging the storage capacitor to a known voltage level before the sensing operation. This preparation step allows the sensing process to start from a defined state, enabling faster measurement without sacrificing accuracy. The capacitor is charged during a programming period before the actual sensing period begins.
Solution Approach 2:
The patent implements periodic action by dividing the sensing process into distinct time periods: a programming period for setting initial conditions, a sensing period for measurement, and a reset period for preparation. This periodic structure allows the system to perform multiple sensing operations in sequence, achieving real-time sensing capability while maintaining measurement precision through standardized periodic cycles.
2Reliability
If the sensing process waits for gate-source voltage to reach threshold voltage naturally, then the measurement is reliable, but the response speed is too slow for real-time display operation
Solution Approach 1:
The patent prepares the measurement system in advance by charging the storage capacitor to a predetermined voltage during the programming period. This preliminary action ensures that when the sensing period begins, all conditions are already set for immediate and reliable measurement, eliminating the need to wait for natural voltage buildup.
Solution Approach 2:
The patent changes the operating parameters by applying specific gate voltages during the programming period that force the transistor into saturation quickly. By controlling the gate voltage to be higher than the threshold voltage during programming, the system achieves rapid establishment of the required voltage conditions, improving response speed while maintaining measurement reliability.
Data Source
AI summary
Disclosed are a device and method for sensing the threshold voltage of a driving TFT included in an organic light emitting display so that a change in the threshold voltage of the driving TFT is sensed during real-time operation by reducing sensing time. First and second sensing voltages are obtained by fast sensing in the TFT linear region, and a change in the threshold voltage of the driving TFT is obtained based on the sensing ratio between the sensing voltages. Thus, a number of processes for deducing a change in threshold voltage, i.e., programming, source node resetting, sensing, and sampling, may be performed during the vertical blanking interval. That is, it is possible to sense a change in the threshold voltage of the driving TFT DT during real-time operation, without the need of arranging a time during power-on or power-off in order to sense a threshold voltage change, thereby improving compensation performance.