LED Display Scan Circuit With Scan-Line Pull-Up for De-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, leading to unnecessary LED illumination and power waste.
Innovation Solution
A novel scan circuit incorporating a low-dropout regulator circuit or a global operational amplifier is integrated to control scan line voltages, preventing ghosting by ensuring that unlit LEDs do not form current paths, thus eliminating ghosting and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional scan circuit is used to drive LED display panels with narrow pixel pitch, then the display resolution is improved, but ghosting occurs due to parasitic capacitance charging
Solution Approach 1:
The patent applies preliminary anti-action by proactively pulling up the voltage of non-current scan lines before they can be charged by parasitic capacitance through LED current. The operational amplifier continuously monitors and maintains the voltage of non-selected scan lines at a high level (close to VDD), preventing the voltage drop that would otherwise occur when adjacent scan lines are activated. This preemptive voltage maintenance blocks the formation of ghosting current paths before they can occur.
Solution Approach 2:
The patent introduces an operational amplifier as an intermediary component between the scan line driver and the scan lines themselves. This operational amplifier acts as a voltage buffer and regulator that isolates the scan lines from each other electrically, preventing parasitic capacitance coupling. By inserting this active voltage control element, the patent mediates the interaction between scan lines and eliminates the harmful capacitive coupling that causes ghosting.
2Productivity
If scan lines are sequentially activated to drive LEDs, then display performance is improved, but parasitic capacitance causes unintended LED illumination
Solution Approach 1:
The patent implements feedback by using the operational amplifier to continuously monitor the voltage level of non-current scan lines and automatically adjust their voltage to maintain it at the desired high level. The operational amplifier compares the actual voltage with the target voltage (VDD) and provides corrective action to eliminate any deviation. This closed-loop feedback ensures that even as scan lines are sequentially activated and parasitic capacitance changes, the voltage of non-selected lines remains stable and prevents unintended LED illumination.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the voltage parameter of non-current scan lines. Instead of allowing the voltage to float or drop due to parasitic capacitance effects, the system actively changes and maintains the voltage parameter at a specific high level. This parameter control transforms the passive scan line voltage behavior into an actively managed parameter, preventing the conditions that lead to ghosting while maintaining display performance.
3Object-affected harmful factors
If a low-dropout regulator circuit or global operational amplifier is added to eliminate ghosting, then ghosting is suppressed, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the operational amplifier to perform multiple functions simultaneously: it acts as a voltage buffer, a voltage regulator, and a parasitic capacitance compensation device all in one component. Rather than adding separate circuits for each function, the single operational amplifier handles voltage maintenance, isolation, and ghosting prevention, thereby reducing the overall circuit complexity compared to using multiple dedicated components for each function.
Data Source
AI summary
A scan circuit applicable to driving a plurality of light-emitting-diodes of a display panel is provided. Each of a plurality of switching components is electrically connected with a scan line of the display panel for determining if the light-emitting-diodes connected to the scan line are conductive. A plurality of power transistors are disposed corresponding to the scan lines, each connected between one scan line and a ground terminal. A low-dropout regulator circuit or global operational amplifier is alternatively connected to the plurality of switching components in common for selectively pulling up a voltage level 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 is significantly reduced at the same time.