OLED Driving Circuit Threshold Voltage Compensation
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Solution Overview
Problem
Active-matrix OLED displays face challenges in accurately displaying gray levels due to hysteresis-related response time variations and smear issues caused by on-bias voltage application, leading to delayed response times and screen sticking.
Innovation Solution
A method of driving the display device that includes specific voltage applications and transistor operations to compensate for threshold voltage variations, reduce hysteresis effects, and prevent smear, involving the use of multiple transistors and a capacitor to manage gate-source voltage and data signal transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a compensation circuit is used to compensate for threshold voltage variation of the first transistor, then threshold voltage compensation is improved, but response time varies due to hysteresis causing gray level display errors
Solution Approach 1:
The patent applies on-bias voltage to the first transistor before the initialization period to pre-compensate for threshold voltage variation. This preliminary action reduces the impact of hysteresis during subsequent gray level transitions, improving response time while maintaining compensation accuracy through the combined operation of the compensation circuit and on-bias voltage application
2Loss of time
If on-bias voltage is applied to the first transistor before initialization to decrease response time, then response time is improved, but characteristic curve changes causing smear on screen
Solution Approach 1:
The patent applies on-bias voltage before initialization to improve response time, then uses the compensation circuit during the initialization period to reset the transistor characteristic curve. This two-stage approach maintains the response time benefit while eliminating the smear effect through subsequent compensation
Solution Approach 2:
The compensation circuit provides feedback to adjust the gate voltage of the first transistor based on its actual threshold voltage. This feedback mechanism corrects the characteristic curve changes caused by on-bias voltage application, preventing gray level display errors and smear on the screen
3Measurement precision
If hysteresis is present in the first transistor, then threshold voltage compensation is achieved, but response time delays occur when transitioning from black to white causing sticking
Solution Approach 1:
The patent applies on-bias voltage to the first transistor before the initialization period to pre-condition the transistor and reduce hysteresis effects. This preliminary action speeds up the response during black-to-white transitions by establishing a more favorable initial operating point, while the compensation circuit maintains accurate gray level control
Data Source
AI summary
A method of driving a display device includes: applying a first voltage at the first transistor to turn on the first transistor; maintaining the first voltage at the first transistor; applying a second voltage lower than the first voltage at the first transistor; wherein the applying of the first voltage comprises switching the fourth transistor according to the second scan signal to couple the gate electrode of the first transistor to the third power source, and switching the fifth transistor according to the light emission control signal to couple the first electrode of the first transistor to the first power source, and the applying of the second voltage comprises switching the second transistor according to the first scan signal to couple the first electrode of the first transistor to the data line, and switching the third transistor according to the first scan signal to diode-couple the first transistor.