Display Panel Calibration Circuit for Threshold Voltage Drift
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Solution Overview
Problem
Existing display panel calibration systems face challenges in accurately sensing and adjusting for threshold voltage drift in driving transistors, leading to uneven brightness and defects due to variations in amplifier gains.
Innovation Solution
A calibrating circuit comprising a pixel sensor, calibration sensors, an amplifying circuit, an analog-to-digital converter, and a gain adjusting circuit that senses terminal voltages, adjusts amplifier gains based on digital code differences, and iteratively refines the gain adjustment to achieve optimal amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a compensation circuit is disposed outside the display panel to sense the threshold voltage, then the threshold voltage can be sensed and used to calibrate the display panel, but different amplifiers may have different gains due to process drift or other factors, leading to measurement precision issues
Solution Approach 1:
The patent applies preliminary action by performing amplifier gain calibration before actual threshold voltage measurement. The system first calibrates each amplifier's gain using known reference voltages, stores the calibration data, and then uses this calibrated information during subsequent threshold voltage sensing operations. This preliminary calibration step ensures that measurement precision is not compromised by amplifier gain variations.
Solution Approach 2:
The patent implements feedback by using the calibrated amplifier gain information to compensate for gain variations during threshold voltage measurement. The system measures the actual gain of each amplifier, feeds this information back into the calculation process, and adjusts the threshold voltage computation accordingly. This feedback mechanism eliminates the reliability issue caused by amplifier gain inconsistency.
2Manufacturing precision
If the threshold voltage of the driving transistor is sensed to compensate for drift, then mura defects can be reduced, but the process drift and amplifier gain variations cause measurement inaccuracies
Solution Approach 1:
The patent introduces an intermediary calibration process that mediates between the amplifier's variable gain and the threshold voltage measurement. Instead of directly measuring threshold voltage with potentially inaccurate amplifier gains, the system first uses the amplifier to measure known reference voltages, calculates the actual gain, and then uses this gain information as an intermediary correction factor in the threshold voltage calculation. This intermediary step ensures manufacturing precision is not compromised by measurement errors.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the measurement approach based on the calibrated amplifier gain parameter. The system changes the effective measurement parameter from a fixed gain assumption to a variable gain value determined through calibration. This parameter adaptation allows accurate threshold voltage measurement even when amplifier characteristics change due to process drift, thereby maintaining brightness uniformity.
Data Source
AI summary
A circuit and a calibrating method are provided. A pixel sensor senses a terminal voltage of a driving transistor during a sensing period. A calibration sensor senses a first predetermined voltage and a second predetermined voltage during a calibration period. An amplifying circuit amplifies the terminal voltage according to a gain, and amplifies the first predetermined voltage and the second predetermined voltage according to the gain. An analog to digital converter converts the amplified terminal voltage into a digital code, and converts the amplified first predetermined voltage into a first digital code and converts the amplified second predetermined voltage into a second digital code. A gain adjusting circuit adjusts the gain according to the first digital code and the second digital code. Accordingly, the gain of the amplifying circuit is calibrated.