Laser Scanning Display Current Control for Overshoot Suppression
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Solution Overview
Problem
Existing laser scanning display technologies experience overshoot and granular noise due to the sudden increase in current across the threshold current value when transitioning from zero to a value greater than or equal to the threshold current, particularly in images with sparse zero-luminance and non-zero luminance pixels, leading to image degradation and contrast issues.
Innovation Solution
A control device for a laser scanning display apparatus that sets the current value below the threshold during non-display areas and adjusts the current value between the threshold and zero during zero-luminance display areas, using a first and second drive current value to minimize overshoot and noise, with the second drive current value being an average of the first and threshold current values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the current is increased from zero to a value greater than or equal to the threshold current value Ith to start scanning the portion where the luminance level is not zero, then the laser device can emit light for display, but a rise time Tr of the laser output becomes long and an overshoot may occur causing image degradation
Solution Approach 1:
The patent applies preliminary action by setting the drive current to a value between zero and the threshold current value during the period for scanning the non-display area, before the actual display scanning begins. This preliminary current setting prepares the laser device to transition smoothly to the threshold current value when display scanning starts, preventing overshoot and long rise time while maintaining the ability to emit light when needed.
2Illumination intensity
If the current is set at zero during the period for scanning the non-display area B1, then the non-display area becomes dark, but when the current is increased to a value greater than or equal to the threshold current value Ith to start scanning, an overshoot occurs causing granular noise in dark portions
Solution Approach 1:
The patent applies preliminary action by pre-setting the drive current to an intermediate value (between zero and threshold current value) during non-display area scanning. This preliminary current level prevents the laser from being completely off, allowing smooth transitions when entering display areas without causing overshoot or granular noise in dark portions of the image.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the drive current parameter to different levels based on the scanning area. Specifically, it sets the current to an intermediate value (not zero, not threshold) during non-display areas, and transitions to threshold current value during display areas with non-zero luminance, thereby controlling both brightness and preventing harmful overshoot effects.
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 effectively suppresses overshoot and granular noise, maintaining image quality by controlling the current values to ensure precise luminance and contrast, thereby reducing image brightness and noise in dark portions.
Implementation Method 1
the laser device spontaneously emits light (spontaneous emission), gradually increases as the drive current I increases
Implementation Method 2
When the drive current I reaches a threshold current value Ith, laser oscillation (stimulated emission) starts
Data Source
AI summary
A control device for a laser scanning display apparatus includes a laser device, a current source that generates an electric current supplied to the laser device, and a controller that controls the current source to set a current value of the electric current supplied to the laser device. During a period for scanning a non-display area where no image is displayed, the controller sets the current value at a first drive current value that is less than a threshold current value at which the laser device starts oscillating; and during a period for scanning a portion with a luminance level of zero in a display area where an image is displayed, the controller sets the current value at a second drive current value that is greater than or equal to the first drive current value and less than the threshold current value.