OLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
In organic light emitting displays, the non-uniformity of the fabricating process leads to varying threshold voltages of driving transistors across pixels, causing uneven luminance even when the same data voltage is applied.
Innovation Solution
The display incorporates a capacitor coupled to the gate and source electrodes of the driving transistor, along with a second transistor that supplies a reference voltage to the source electrode, allowing for compensation of the threshold voltage and uniform luminance across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the same data voltage is applied to each pixel, then the data voltage consistency is maintained, but the luminance uniformity deteriorates due to threshold voltage variations
Solution Approach 1:
The capacitor stores a compensation voltage that compensates for the threshold voltage of the driving transistor before the data voltage is applied. This preliminary compensation action ensures that even though the same data voltage is applied to each pixel, the actual voltage at the gate electrode accounts for threshold voltage variations, thereby maintaining luminance uniformity without increasing data voltage complexity
Solution Approach 2:
The capacitor acts as an intermediary element between the data line and the gate electrode of the driving transistor. It stores a compensation voltage that mediates the effect of threshold voltage variations, allowing the same data voltage to produce uniform luminance across pixels with different threshold voltages
2Illumination intensity
If a compensation circuit is added to each pixel, then the luminance uniformity is improved, but the device complexity increases
Solution Approach 1:
The compensation mechanism is implemented locally within each pixel using a capacitor that stores a compensation voltage specific to that pixel's driving transistor threshold voltage. This local compensation approach improves luminance uniformity without requiring complex global compensation circuits, as each pixel independently handles its own threshold voltage variation
Solution Approach 2:
The capacitor changes the voltage parameter at the gate electrode by storing a compensation voltage that offsets the threshold voltage. This parameter change allows the driving transistor to operate with the correct effective gate voltage despite variations in threshold voltage, thereby improving luminance uniformity with a simple capacitor component
Data Source
AI summary
An organic light emitting display including a display panel having pixels coupled to data lines and first power voltage lines. Each of the pixels includes an organic light emitting diode; a driving transistor coupled to the organic light emitting diode and the first power voltage lines; a first transistor coupled to the data lines and a gate electrode of the driving transistor; a second transistor configured to supply a reference voltage of the data lines to a source electrode of the driving transistor; and a capacitor coupled to the gate and source electrodes of the driving transistor.