Pixel Driving Circuit Dynamic Reference Voltage Switching
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Solution Overview
Problem
Organic light emitting display devices experience luminance differences and non-uniformity due to variations in the inherent characteristics of driving transistors, which are affected by deterioration over time, leading to deviations in threshold voltage and mobility.
Innovation Solution
An electronic device with a pixel driving circuit that operates in both light emitting and sensing modes, utilizing a reference voltage line with different voltage levels to accurately measure and compensate for the inherent characteristics of driving transistors, reducing parasitic capacitance differences and improving sensing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single reference voltage is applied to the reference voltage line, then the circuit structure is simple, but parasitic capacitance differences cause sensing inaccuracy
Solution Approach 1:
The reference voltage line dynamically switches between first and second reference voltages based on the operation mode (light emitting mode or sensing mode). This dynamic voltage switching allows the system to compensate for parasitic capacitance differences without requiring a completely separate reference line, thus improving sensing accuracy while maintaining relatively simple circuit structure
Solution Approach 2:
The patent changes the voltage parameter of the reference voltage line from a fixed single voltage to a variable voltage that can be switched between first reference voltage (higher than ELVDD) and second reference voltage (lower than ELVDD). This parameter change enables the system to adapt to different operational requirements and eliminate sensing errors caused by parasitic capacitance
2Manufacturing precision
If driving transistors are used with inherent characteristic variations, then the device can be manufactured with standard processes, but luminance non-uniformity occurs
Solution Approach 1:
The patent implements a feedback mechanism where the sensing transistor measures the voltage at the first node during sensing mode, which reflects the inherent characteristics of the driving transistor. This measured information is then used to compensate for threshold voltage shifts and mobility variations, thereby correcting luminance non-uniformity while maintaining standard manufacturing processes
Solution Approach 2:
The pixel circuit performs self-diagnosis and self-compensation by using the sensing transistor to measure its own driving transistor's characteristics and adjusting its operation accordingly. This self-service approach eliminates the need for external calibration equipment or complex additional circuits, maintaining manufacturing simplicity while improving luminance uniformity
Data Source
AI summary
An electronic device includes a pixel driving circuit to operate in a light emitting mode or a sensing mode and including a reference voltage line for receiving a reference voltage comprising a first reference voltage and a second reference voltage different from the first reference voltage and a light emitting diode including a first electrode, a light emitting element, and a second electrode. The light emitting diode has in an on-state or an off-state in the light emitting mode, the first reference voltage is applied to the reference voltage line in the light emitting mode, a first voltage is applied to the first electrode in the off-state, a second voltage is applied to the first electrode in the on-state, the sensing mode includes an initialization period and a sensing period, and the second reference voltage is applied to the reference voltage line in the initialization period.