LED Backlight Ghost Cancellation via Discharge Switches
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Solution Overview
Problem
Ghosting phenomena occur in electronic devices with displays due to parasitic capacitance, causing unintended light emission from LEDs that are intended to be off, leading to reduced image quality and increased energy consumption.
Innovation Solution
The implementation of a ghost cancellation architecture that includes a discharge switch to discharge the common anode of LEDs and a precharge switch to precharge the common cathode, preventing undesired current paths and reducing parasitic capacitance effects, thereby controlling illumination and minimizing energy loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If time-multiplexed LEDs are used to control illumination, then energy consumption is reduced, but parasitic capacitance causes ghost current spikes that produce ghosting effects
Solution Approach 1:
The patent applies preliminary anti-action by implementing discharge switches that actively remove parasitic charge from LED common anodes or cathodes before the next illumination cycle begins. This pre-emptive discharge prevents ghost current spikes that would otherwise cause visible ghosting effects, allowing the time-multiplexed LED system to operate without the harmful artifacts while maintaining low energy consumption.
Solution Approach 2:
The patent introduces discharge switches as intermediary components between the power supply voltage and the LED arrays. These switches act as mediators that selectively couple discharge voltage levels to common anodes or cathodes, enabling controlled removal of parasitic capacitance without interfering with the normal illumination function. This intermediary mechanism resolves the conflict between energy efficiency and ghosting prevention.
2Manufacturing precision
If discharge switches are added to cancel ghosting, then image quality is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the LED array control into separate, independently controlled segments. Discharge switches are selectively placed at specific common anodes or cathodes based on the display content requirements, rather than uniformly across all LEDs. This segmented approach improves image quality where needed while minimizing the overall number of discharge switches required, thus balancing image quality improvement with device complexity.
Solution Approach 2:
The patent implements local quality by applying ghost cancellation only to specific LED rows or columns where ghosting would be visually noticeable based on the display content. The control circuitry selectively activates discharge switches for particular LED segments rather than all LEDs simultaneously, providing high image quality in critical areas while reducing the overall circuit complexity and power consumption associated with universal discharge switching.
3Ease of operation
If parasitic capacitance is not discharged, then circuit operation is simpler, but undesired current paths cause ghosting and energy loss
Solution Approach 1:
The patent applies preliminary action by discharging parasitic capacitance on the leading edge of the clock cycle, before the main illumination phase begins. This timing ensures that undesired current paths are eliminated before they can cause ghosting or energy loss during the active display period. The discharge operation is completed in advance, maintaining simple circuit operation during the critical illumination phase while still preventing energy loss.
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 solution effectively prevents ghosting effects, enhances image quality, and reduces energy consumption by ensuring accurate control over LED illumination, even during transitions between rows, thereby improving the overall performance of electronic devices with displays.
Implementation Method 1
parasitic capacitance, which generates a ghost current spike and forces the time-multiplexed LEDs to emit a brief flash of light
Implementation Method 2
pre-charge the common cathode to prevent an undesired current path through the array of LEDs by barely turning the array of LEDs off or reverse-biasing the array of LEDs
Data Source
AI summary
Aspects of the subject technology relate to an electronic device with a display. The display includes a first array of light-emitting diodes of a backlight unit to generate backlight for the display with each LED including an anode and a cathode. A first switch selectively couples a power supply voltage to a common anode of the first array of LEDs to control illumination of the first array of LEDs. A first discharge switch selectively couples a first voltage level to the common anode of the first array of LEDs to discharge the common anode to prevent an undesired current path through the first array of LEDs and associated undesired illumination.