OLED Driving Transistor Threshold Voltage Compensation Circuit
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Solution Overview
Problem
The organic light emitting diode display faces issues with threshold voltage instability in driving transistors due to prolonged application of gate voltage, leading to degradation and reduced display quality and lifespan.
Innovation Solution
A compensation circuit is introduced that applies a compensation voltage of opposite polarity to the driving transistor's gate terminal, along with a constant current, to shift and maintain the threshold voltage at a reference value, thereby stabilizing the transistor's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If gate voltage is continuously applied to drive the organic light emitting diode display, then the display can operate and emit light, but the threshold voltage of the driving transistor degrades and shifts over time
Solution Approach 1:
The patent applies periodic compensation voltages with opposite polarity to the driving transistor gate during non-display periods (horizontal and vertical blanking intervals). This periodic action reverses the threshold voltage shifts caused by continuous forward bias, maintaining voltage stability over extended operation durations without affecting normal display functionality.
2Reliability
If a compensation circuit is added to stabilize threshold voltage, then threshold voltage stability improves, but device complexity increases
Solution Approach 1:
The compensation circuit uses the display system's own existing resources - the driving transistor itself and available blanking intervals - to perform self-compensation. By applying reverse polarity voltages during non-display periods, the system automatically corrects its own threshold voltage drift without requiring external intervention or complex additional circuitry.
Solution Approach 2:
The patent changes the voltage parameter applied to the driving transistor gate by introducing compensation voltages of opposite polarity during specific time intervals. This parameter change (applying negative or reduced voltage during blanking periods) counteracts the cumulative effect of forward bias, stabilizing the threshold voltage without fundamentally altering the transistor structure.
Data Source
AI summary
An organic light emitting diode display compensates for a threshold voltage of a thin-film driving transistor to improve display quality. The display includes a light emitting cell connected between a high-level voltage source and a first node. A driving transistor is connected between the first node and a ground voltage source to control a current, which flows in the light emitting cell, by using a voltage applied to a gate terminal of the driving transistor. A data driving circuit applies a data voltage of first polarity to the gate terminal of the driving transistor to shift a threshold voltage of the driving transistor from a reference value to the voltage of first polarity. A compensation circuit supplies a compensation voltage of second polarity to the gate terminal of the driving transistor to shift the threshold voltage of the driving transistor from the voltage of first polarity to the voltage of second polarity, and then supplies a constant current to the gate terminal of the driving transistor to restore the threshold voltage of the driving transistor to the reference value.