Active Matrix Screen Digital Control Method for OLED Luminosity
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Solution Overview
Problem
Existing digital control methods for active matrix screens, such as OLEDs, require high operating frequencies to modulate pixel luminosity, leading to significant power consumption and heat dissipation issues, especially when addressing large formats, and result in luminosity losses due to frequent addressing of pixels.
Innovation Solution
A digital control method that reduces the frequency of addressing pixels by writing luminosity bits in a sequence that spans multiple periods, allowing each bit to activate the display component for a duration proportional to its weight in the binary word, thereby minimizing error and maintaining concordance between bit values and activation durations across a frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital control methods are used to modulate pixel luminosity, then luminosity control precision is improved, but operating frequency increases leading to higher power consumption and heat dissipation
Solution Approach 1:
The patent applies periodic action by using pulse width modulation (PWM) to control diode luminosity. Instead of continuously adjusting voltage, the system applies periodic pulses with varying widths where the duty cycle corresponds to the desired luminosity level. This periodic switching approach maintains precise digital control while reducing average power consumption compared to analog voltage regulation.
Solution Approach 2:
The patent replaces the mechanical/analog voltage regulation system with a digital switching system. Instead of using variable resistors or analog amplifiers to control diode brightness, the invention uses digital logic circuits that generate PWM signals. This substitution eliminates the continuous power dissipation associated with analog control elements while maintaining precise luminosity control through digital bit sequences.
2Measurement precision
If digital control methods are used to modulate pixel luminosity, then luminosity control precision is improved, but heat dissipation increases
Solution Approach 1:
The periodic PWM switching reduces heat dissipation by keeping the switching transistor in a low-resistance state during conduction periods. The transistor either fully conducts (low Rds(on)) or fully blocks, avoiding the high-power dissipation region of partial conduction. This periodic on-off action maintains precise luminosity control while minimizing thermal generation compared to analog voltage control.
Solution Approach 2:
The patent substitutes analog voltage control with digital PWM switching, replacing continuous power dissipation in analog control circuits with efficient digital switching. The digital logic generating PWM signals consumes minimal power compared to analog amplifiers or variable resistors, and the switching transistor dissipates less heat due to its operation in saturated or cutoff regions rather than the active region.
3Measurement precision
If high operating frequency is used to address pixels, then luminosity modulation precision is improved, but luminosity loss increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the optimal PWM duty cycles corresponding to each possible luminosity level in lookup tables before display operation. This pre-computation allows the system to directly retrieve the appropriate pulse width for any desired luminosity level without requiring high-frequency real-time calculations, thereby maintaining precision while reducing operating frequency and associated luminosity losses.
Solution Approach 2:
The patent uses partial action by implementing an N-bit binary control system that provides 2^N luminosity levels, which is sufficient for human visual perception without requiring excessive frequency. The human eye's temporal integration effectively averages the PWM pulses, allowing lower frequencies to achieve the same perceived luminosity precision that would require higher frequencies with continuous control methods.
4Ease of operation
If follower transistors work in saturated mode to control diode supply, then luminosity control is achieved, but power dissipation increases causing heating
Solution Approach 1:
The patent replaces the saturated-mode follower transistor configuration with a digital switching architecture. Instead of using the transistor in its linear saturated region where it dissipates power as (Vcc - Vdiode) × Idiode, the invention uses the transistor as a switch that operates in cutoff or deep saturation with minimal conduction time. The PWM control signal drives the transistor to switch rapidly between off and low-resistance on states, maintaining luminosity control while dramatically reducing average power dissipation and heat generation.
Data Source
Figure 1~2c
Figure 3
Figure 4a~4d
AI summary
The invention relates to a method for displaying images on an active matrix screen (10), where i represents a pointer to a current line. Each pixel comprises a memory and a display component. The method consists of controlling the brightness of each pixel by means of a binary word comprising several bits (LSB...MSB) written successively to the memory, and by controlling the display component according to the state of the bit written to the memory. The bits of each binary word are arranged according to their weight from j=1 to j=P. The following writing operations are performed sequentially: • starting from a current line i, write to lines i+2j, from j=1 to j=P, the bit of weight j of each binary word associated with the different pixels of lines i+2j; • repeat the above writing operations 2P-1 times, shifting the pointer i of the current line by one unit with each repetition; i being determined modulo 2P-1 so as to be between 1 and 2P-1.