Active Matrix Display Voltage Drop Compensation
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Solution Overview
Problem
Active-matrix LED and OLED displays face non-uniformities and degradation due to variations in production processes, material properties, and aging, leading to inefficiencies in current distribution and image quality, with existing solutions increasing power consumption and complexity.
Innovation Solution
A driving circuitry system that uses a data driver module, line-drivers, and calibration means to maintain uniform current across pixels by flowing a reference current through power supply lines, determining voltage drops, and adjusting pixel voltages using a calibration look-up table and interpolation unit, eliminating the need for additional current sources and DACs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DAC is added in each column to compensate for voltage drops, then voltage drop compensation is achieved, but circuit complexity increases and additional parasitic effects are introduced
Solution Approach 1:
The patent combines the voltage drop compensation function with the existing data driver circuitry by using the same data lines to carry both image data and compensation signals. The compensation voltage is integrated into the data signal path, eliminating the need for separate compensation circuits and reducing overall system complexity.
Solution Approach 2:
The data lines are designed to serve multiple functions: transmitting image data to pixels and simultaneously carrying voltage drop compensation signals. This multi-functional approach allows the existing infrastructure to handle compensation without requiring additional dedicated circuits, thereby reducing device complexity while maintaining compensation accuracy.
2Measurement precision
If fine tuning of current in every pixel is implemented by driving the drive transistor as a current source, then current accuracy is improved, but power consumption increases due to higher source-drain voltage
Solution Approach 1:
The patent changes the operating parameters of the drive transistor by adjusting the source-drain voltage dynamically. Instead of maintaining a consistently high voltage for current source operation, the system optimizes the voltage level based on the specific pixel requirements and compensation needs, thereby reducing overall power consumption while maintaining sufficient current accuracy.
3Measurement precision
If twice the number of contact pads are used to drive the display with current sources for every line, then uniform current is achieved, but parasitic effects increase and wafer area is consumed
Solution Approach 1:
The patent merges the data signal transmission and power supply functions into a single integrated approach. By using the data lines to carry both image information and compensation signals, the system achieves uniform current distribution without requiring separate power supply lines for each row, thereby reducing the number of contact pads needed.
Solution Approach 2:
The data lines perform multiple functions simultaneously: they transmit image data to the pixels and provide the path for voltage drop compensation signals. This multi-functional use of existing lines eliminates the need for additional dedicated power supply lines and contact pads, reducing device complexity while maintaining current uniformity.
Data Source
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AI summary
Driving system circuitry for an active matrix display comprises: a data driver module for receiving a digital data bit stream representing an image to be displayed by pixels of the active matrix display, one or more power supply lines for powering a plurality of pixels each comprising at least one light emitting element, a voltage source connected to the one or more power supply lines, and calibration means for compensating for power drop over the one or more supply lines. The calibration means comprise means for flowing a current through an individual pixel, means for determining a voltage drop across the pixel and for comparing this to a pre-determined reference voltage for that pixel, means for determining, from the comparison, calibration values for that pixel which take into account resistance of wiring connected to the voltage source and to ground, and means for applying the calibration values to a received digital data bit stream to generate therefrom data driver voltages to be applied to the data driver module for representation of a corrected image.