Inorganic LED Display Driving With Current Sensing and PWM Correction
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Solution Overview
Problem
Display devices using inorganic light emitting elements face issues with color reproducibility and brightness uniformity due to variations in driving current and transistor characteristics, leading to decreased image quality and increased power consumption.
Innovation Solution
A display device with a pixel array and sub-pixel circuits that include a driving transistor, a driver to set image data voltage, a sensing unit to monitor current flow, and a correction unit to adjust voltage based on sensed data, allowing for improved control of inorganic light emitting elements and reduced peak power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If inorganic light emitting elements are driven using pulse amplitude modulation (PAM) with varying driving current to represent gray scales, then the gray scale control is achieved, but the wavelength of emitted light changes causing decrease in color reproducibility
Solution Approach 1:
The patent employs pulse width modulation (PWM) instead of pulse amplitude modulation (PAM), using periodic on/off switching of the driving current at fixed amplitude. The gray scale is represented by varying the duty cycle (width) of the pulses rather than the amplitude, which prevents wavelength shift while achieving gray scale control. This periodic action maintains constant current amplitude to avoid color change.
Solution Approach 2:
The patent changes the control parameter from current amplitude (PAM) to pulse width/duty cycle (PWM). By keeping the current amplitude constant and varying only the temporal width of the pulses, the system achieves gray scale representation without causing wavelength shifts that occur when current amplitude is varied. This parameter transformation resolves the color reproducibility issue.
2Ease of operation
If driving current magnitude is varied to control gray scale of sub-pixels, then gray scale representation is achieved, but brightness uniformity degrades due to differences in threshold voltage and mobility of driving transistors
Solution Approach 1:
The patent incorporates a sensing unit that measures the actual current flowing through each driving transistor and feeds this information back to a correction unit. The correction unit adjusts the PWM duty cycle or current amplitude based on the sensed current and stored compensation values, compensating for transistor parameter variations. This feedback mechanism ensures uniform brightness across all sub-pixels despite differences in threshold voltage and mobility.
Solution Approach 2:
The patent performs preliminary compensation by storing correction values for each sub-pixel in advance, based on sensed current characteristics. Before normal display operation, the system characterizes each transistor and pre-calculates compensation parameters. This preliminary action allows the system to preemptively correct for transistor variations, ensuring brightness uniformity from the start without requiring real-time complex adjustments.
3Productivity
If all sub-pixel circuits are driven simultaneously to display an image, then the display refresh rate is maintained, but peak power consumption increases
Solution Approach 1:
The patent divides the row lines into multiple groups and drives sub-pixel circuits in sequential groups rather than all simultaneously. Each group is driven during a specific time period, with non-current groups in a low-power state. This segmentation of the driving process reduces the number of active circuits at any given moment, thereby reducing peak power consumption while maintaining overall display refresh performance through the cumulative effect of all groups.
Solution Approach 2:
The patent implements periodic driving by sequentially activating different groups of row lines in alternating time periods. Each group is driven for a specific duration, then deactivated while the next group is activated. This periodic switching pattern ensures that not all circuits draw current simultaneously, reducing peak power demand while the cumulative display effect maintains the required refresh rate through the coordinated sequencing of all groups.
Data Source
AI summary
A display device includes a display panel including a pixel array including a plurality of pixels and a plurality of sub-pixel circuits, each pixel of the plurality of pixels including a plurality of inorganic light emitting elements and a sub-pixel circuit of the plurality of sub-pixel circuits being provided for an inorganic light emitting element of the plurality of inorganic light emitting elements, a driver configured to set the image data voltage to sub-pixel circuits included in each of the plurality of row lines in an order of the row lines, a sensing unit configured to sense a current flowing in a driving transistor included in the sub-pixel circuit based on a specific voltage applied to the sub-pixel circuit, and output sensing data corresponding to the sensed current, and a correction unit configured to correct the image data voltage applied to the sub-pixel circuit based on the sensing data.