OLED Data Driving Circuit Brightness Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Light emitting displays face challenges in achieving uniform brightness due to variations in transistor threshold voltage and electron mobility, which affect the consistency of image display.
Innovation Solution
A data driving circuit that generates compensation data based on current supplied to a current sink from pixels, using this data to select appropriate gradation voltages for uniform brightness, incorporating a switching unit, buffer, gamma voltage generator, and digital-analog converter to adjust and transmit data signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional data driving circuits are used without compensation, then the circuit structure is simple, but the brightness uniformity across pixels deteriorates due to transistor parameter variations
Solution Approach 1:
The patent applies preliminary action by measuring and storing compensation data for each pixel before actual display operation. The compensation data, which accounts for transistor threshold voltage and electron mobility variations, is pre-calculated and stored in memory during a calibration phase. During normal operation, this pre-stored compensation data is retrieved and applied to adjust the data signals, eliminating the need for real-time complex measurements and enabling brightness uniformity without adding operational complexity.
Solution Approach 2:
The patent introduces compensation data as an intermediary element that mediates between the raw input signal and the final pixel drive signal. This compensation data acts as a corrective layer that adjusts for transistor variations. The system uses a lookup table or memory structure that stores pre-calculated compensation values, which are then combined with the original display data to produce corrected signals that compensate for manufacturing variations in transistor characteristics.
2Manufacturing precision
If pixel characteristics are compensated for using additional circuits, then brightness uniformity is improved, but the pixel circuit complexity increases
Solution Approach 1:
The patent extracts the compensation function from the pixel circuit itself and relocates it to the data driving circuit. Instead of adding compensation transistors, capacitors, or additional circuit elements within each pixel, the invention removes the compensation responsibility from the pixel level and handles it at the driver level using external memory and lookup tables. This extraction maintains pixel circuit simplicity while achieving brightness uniformity through external compensation mechanisms.
Solution Approach 2:
The patent uses copying by creating a digital representation of pixel characteristics in the form of compensation data stored in memory. Rather than physically replicating compensation circuitry for each pixel, the system creates a digital copy or model of each pixel's characteristics and uses this copied information to adjust drive signals. The lookup table stores copied characteristic data that enables software-based compensation without hardware duplication.
3Reliability
If transistor parameter variations are not compensated, then the device complexity remains low, but the image display quality deteriorates due to non-uniform brightness
Solution Approach 1:
The patent implements feedback by using measured pixel characteristics to generate compensation data that feeds back into the signal processing chain. During an initial calibration phase, the actual transistor parameters are measured, and this measurement feedback is used to create compensation values. The compensation data then feeds back into the normal display operation, continuously correcting for variations. This closed-loop feedback approach ensures reliable image display quality while keeping the operational circuit relatively simple.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A data driving circuit for a light emitting display may include a gamma voltage generator that generates gradation voltages, a current sink that receives a predetermined current from a pixel via a data line during a first partial period of one complete period for driving the pixel, a voltage generator that generates an incrementally increasing compare voltage during the first partial period, a comparator that compares a compensation voltage generated based on the predetermined current with the compare voltage and generates a logic signal based on a result of the compare, an adjusting unit that generates compensation data based on the logic signal, and a digital-analog converter that generates a composite data using the compensation data and externally supplied data and selects, as a data signal for the pixel, one of the plurality of gradation voltages based on a bit value of the composite data.