LED Array Billboard Ghost Image Compensation Circuit
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Solution Overview
Problem
Conventional LED array billboards suffer from 'ghost images' due to parasitic capacitors in line and channel switch circuits, leading to upper and lower ghost images, and struggle with low gray scale compensation.
Innovation Solution
Incorporating ghost image compensation switch circuits and a control circuit that provides a ghost image compensation voltage to channel nodes when LEDs are not conductive, and adjusting the channel operation signal for gray scale compensation by extending the duty period and adding a gray scale compensation period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional line switch circuits and channel switch circuits are used in LED array billboard, then the device structure is simple, but ghost images appear due to parasitic capacitors
Solution Approach 1:
The patent extracts and addresses the harmful effect of parasitic capacitors by introducing separate compensation circuits. The line compensation switch circuit and channel compensation switch circuit are independently added to compensate for the charge stored in parasitic capacitors CR and CC, thereby eliminating ghost images without fundamentally changing the original simple switching structure
Solution Approach 2:
The patent introduces compensation capacitors and compensation switch circuits as intermediary elements between the power supply and the LED array. These intermediary components store and release compensatory charges to counteract the harmful effects of parasitic capacitors, thereby improving image quality without requiring complete redesign of the basic circuit architecture
2Reliability
If parasitic capacitors are present in switch circuits, then the circuit operation is simple, but upper and lower ghost images occur
Solution Approach 1:
The patent applies preliminary action by pre-charging the compensation capacitors before the main switching operation. The control circuit charges the line compensation capacitor and channel compensation capacitor in advance during the non-display period, so that when the parasitic capacitors discharge and cause ghost images, the compensatory charges are already in place to counteract the harmful effects
Solution Approach 2:
The patent implements feedback control through the control circuit that monitors the switching states and adjusts the compensation signals accordingly. The control circuit generates compensation signals based on the operating state of the LED array, creating a feedback loop that dynamically adjusts the compensatory charges to eliminate ghost images in real-time
3Measurement precision
If duty period is extended for gray scale compensation, then gray scale accuracy is improved, but illumination time increases
Solution Approach 1:
The patent segments the illumination period into distinct phases: the normal duty period for primary illumination and the gray scale compensation period for precision control. By separating these functions into different time segments, the system can maintain accurate gray scale representation without requiring the entire illumination period to be extended, thus balancing precision with temporal efficiency
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
Effectively eliminates ghost images and improves gray scale accuracy by ensuring proper voltage management and extended illumination periods for improved brightness control.
Implementation Method 1
The LED array 110 includes plural LEDs (LED1A∼LED4D)
Implementation Method 2
an LED current flows through the LED LED3B at line N and channel CH3 to turn ON the LED LED3B
Implementation Method 3
The reason to cause the upper ghost image is due to the parasitic capacitor CR in the line switch circuits 120
Data Source
AI summary
The present invention discloses a light emitting device array billboard and a control method thereof. The light emitting device array billboard includes a light emitting device array circuit, plural line switch circuits, plural channel switch circuits, plural ghost image compensation switch circuits, and a control circuit. The control circuit operates the line switch circuits and the channel switch circuit to turn ON a selected light emitting device for a duty period in a lighting period, and operates the plural ghost image compensation switch circuits to electrically connect a channel node corresponding to the selected light emitting device to a ghost image compensation voltage after the lighting period. The control circuit further adjusts a channel operation signal according to a gray scale compensation signal, to turn ON the selected light emitting device for a gray scale compensation period in addition to the duty period.