OLED Passive Matrix Drive Signal Adjustment for Power Reduction
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Solution Overview
Problem
Passive matrix electro-luminescent displays face challenges with high power consumption due to the need for high currents to maintain light emission and overcome capacitive charging, leading to reduced lifetime and increased cross-talk between pixels, limiting their application to small displays with fewer lines.
Innovation Solution
A method is introduced to adjust drive signals based on the change in total capacitive charge between image fields, reducing the power required to charge and discharge capacitors and minimizing resistive losses, allowing for higher resolution and larger displays by optimizing the drive signals for each pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high currents are provided to each light-emitting element to achieve reasonable time-averaged luminance, then luminance is improved, but lifetime is reduced and cross-talk between pixels increases
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitors associated with each light-emitting element before the actual display period. This pre-charging phase stores electrical energy in the capacitors, which then discharges during the display period to sustain light emission. This approach eliminates the need for high peak currents during the display period, thereby extending the lifetime of the light-emitting elements while maintaining adequate luminance.
2Illumination intensity
If high currents are provided to each light-emitting element to achieve reasonable time-averaged luminance, then luminance is improved, but cross-talk between pixels increases
Solution Approach 1:
By pre-charging the capacitors before the display period, the patent ensures that the capacitors are already charged and ready to discharge during the display period. This preliminary charging action isolates the pixel activation process, preventing current leakage to adjacent pixels and reducing cross-talk between pixels while maintaining the required luminance levels.
3Device complexity
If time division multiplexing is employed to drive the display, then device complexity is reduced, but resistive voltage and power losses across the electrodes increase
Solution Approach 1:
The patent introduces a pre-charge phase before each display period, where capacitors are charged in advance. This preliminary action allows the actual display period to use lower currents, significantly reducing resistive I²R power losses in the row and column electrodes. Although this adds some complexity to the drive timing, it maintains the benefits of time division multiplexing while dramatically improving power efficiency.
4Measurement precision
If the number of lines in the display is increased to achieve higher resolution, then measurement precision is improved, but power consumption increases significantly
Solution Approach 1:
By pre-charging the capacitors before the display period, the patent enables higher resolution displays with more lines to be driven with significantly lower power consumption. The pre-charged capacitors sustain light emission during the display period without requiring continuous high currents, making it feasible to drive high-resolution displays with a reasonable number of addressable lines while maintaining low power consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces power consumption, extends the lifetime of the display, and improves image quality by minimizing the need for precharging and discharging capacitors, thereby reducing peak currents and resistive losses.
Implementation Method 1
EL materials are deposited between these electrodes, such that when a positive electrical potential is created between the two electrodes, the EL material between these two electrodes emits light
Implementation Method 2
each light-emitting element has an effective capacitor having a significant capacitance that must be overcome before light emission can occur
Data Source
AI summary
A method of controlling a passive matrix display having rows and columns of pixels including receiving an input image signal; determining drive signals for at least a first image field and a second image field; calculating a value that is correlated to a change in the total capacitive charge of the pixels that will occur between the display of the first image field and the second image field for at least one column of the passive-matrix, electro-luminescent display; adjusting at least one of the drive signals within first or second image fields to compensate for the change in total capacitive charge; and providing adjusted drive signals for each pixel.