Light Emitting Display Pixel Circuit Offset Voltage Compensation
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Solution Overview
Problem
Light emitting display apparatuses face challenges in maintaining uniform image quality due to variations in threshold voltage of driving transistors, leading to differences in current flow across pixels, which are not effectively compensated by existing internal compensation circuits.
Innovation Solution
The apparatus operates in distinct periods: initialization, sampling, offset voltage formation, data writing, and light emission, with an extended offset voltage formation period to form a data offset voltage, compensating for sampling voltage variations and threshold voltage differences between pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an internal compensation circuit is used to sample threshold voltage during a sampling period, then threshold voltage compensation is achieved, but sampling voltage variation occurs between pixels due to threshold voltage variation between driving transistors, leading to image quality deterioration
Solution Approach 1:
The patent applies preliminary action by extending the offset voltage formation period before the sampling period to pre-form an offset voltage that compensates for threshold voltage variations. This offset voltage is formed in advance and stored in the capacitor, so when sampling occurs, the sampling voltage already includes this pre-formed offset compensation, eliminating the need for separate threshold voltage sampling and storage operations.
Solution Approach 2:
The patent changes the timing parameters by extending the offset voltage formation period to be longer than the sampling period. This parameter change allows sufficient time for the offset voltage to be fully formed and stored before sampling begins, ensuring that the compensation voltage is stable and accurate, thereby preventing sampling voltage variation between pixels.
2Loss of time
If the sampling period is used to store threshold voltage in a capacitor, then compensation is performed, but the sampling period is insufficient to account for threshold voltage variations, causing voltage variation between pixels
Solution Approach 1:
The patent performs the offset voltage formation in advance during an extended period before sampling. This preliminary action ensures that the compensation voltage is fully established before the sampling operation begins, allowing the sampling period to be shorter while still achieving accurate compensation.
Solution Approach 2:
The patent changes the duration parameter by making the offset voltage formation period longer than the sampling period. This parameter adjustment ensures that the offset voltage has sufficient time to form and stabilize, improving the accuracy of the compensation voltage stored in the capacitor.
Data Source
AI summary
A light emitting display apparatus includes a light emitting display panel including a plurality of pixels each operating in order of an initialization period, a sampling period, an offset voltage formation period, a data writing period, and a light emission period; a data driving circuit configured to supply data voltage to each of the pixels; a gate driving circuit configured to provide, to each of the pixels, a control signal having voltage levels determined for the initialization period, the sampling period, the offset voltage formation period, the data writing period, and the light emission period of a corresponding pixel; and a timing controller configured to control the data driving circuit and the gate driving circuit, wherein the offset voltage formation period is longer than the sampling period.