LED Scan Circuit With Voltage Clamping to Prevent Display Ghosting
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Solution Overview
Problem
Conventional LED display panels suffer from ghosting issues, particularly upside ghosting, due to parasitic capacitance and signal coupling, which worsen with narrower pixel pitches, affecting display performance and causing unnecessary power consumption.
Innovation Solution
A novel scan circuit incorporating a low-dropout regulator circuit or a global operational amplifier is integrated with switching components and power transistors to selectively raise the voltage level of inactive scan lines, preventing ghosting by blocking current paths and reducing signal coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional scan circuit is used to drive LED display panels, then the circuit structure is simple, but ghosting occurs due to parasitic capacitance charging when transitioning between scan lines
Solution Approach 1:
The patent introduces a voltage regulation circuit as an intermediary component between the scan line driver and the LED array. This circuit includes a voltage regulator and switching elements that actively control the voltage potential of non-active scan lines, preventing parasitic capacitance from charging to levels that would cause ghosting. The intermediary circuit isolates the problematic interaction between scan lines and LED pixels during transitions.
Solution Approach 2:
The patent implements preliminary voltage clamping action by maintaining non-active scan lines at a controlled low voltage potential before the active scan line transitions. The voltage regulation circuit proactively prevents voltage buildup on inactive scan lines during the transition period, eliminating the condition that would lead to ghosting before it can occur.
2Manufacturing precision
If the pixel pitch of the LED display panel is reduced to increase resolution, then the display quality improves, but ghosting becomes more severe
Solution Approach 1:
The voltage regulation circuit serves as an intermediary that decouples the relationship between pixel pitch reduction and ghosting severity. By actively controlling scan line voltages regardless of the physical distance between pixels, the circuit prevents parasitic capacitance effects from becoming more problematic as pixel density increases.
Solution Approach 2:
The patent changes the voltage parameter of non-active scan lines from floating or high potential to a controlled low voltage state. This parameter change in scan line voltage levels prevents the parasitic capacitance from charging to ghosting-causing levels, effectively counteracting the increased susceptibility to ghosting that comes with narrower pixel pitches.
3Use of energy by stationary object
If scan lines are sequentially driven without voltage control, then the circuit operation is simple, but current leaks through unlit LEDs causing power waste
Solution Approach 1:
The voltage regulation circuit acts as an intermediary that controls the electrical state of non-active scan lines. By inserting this circuit between the scan line driver and the LED matrix, it actively prevents current leakage paths through unlit LEDs while maintaining simple sequential driving operation.
Solution Approach 2:
The patent changes the voltage parameter of non-active scan lines to a low potential state during inactive periods. This parameter change creates a voltage barrier that prevents current from flowing through LED pixels that should remain unlit, thereby eliminating power waste without complicating the overall driving scheme.
Data Source
AI summary
A scan circuit applicable to driving a plurality of light-emitting-diodes of a plurality of scan lines of a display panel is provided. A plurality of switching components are configured, having each switching component connected with one of the scan lines. A plurality of power transistors are disposed corresponding to the scan lines, having each power transistor connected between one scan line and a ground terminal. A low-dropout regulator circuit or a global operational amplifier is alternatively connected to the plurality of switching components in common for selectively generating an output voltage to at least one of the scan lines and avoiding ghost imaging on the display panel. By employing the proposed scan circuit, the invention is effective in achieving de-ghost functioning and avoiding conventional signal coupling issues on the display panel. In addition, redundant power waste consumption can be significantly reduced at the same time.