Pre-discharge Circuit for LED Display Brightness Uniformity
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Solution Overview
Problem
Multiplexed LED displays experience brightness differences between rows due to variations in forward voltages across LEDs, leading to uneven display intensity.
Innovation Solution
A pre-discharge circuit is introduced, with a separate discharge circuit connected to each column output, which discharges the stored charge before the output driver circuit activates, reducing parasitic capacitance voltages and mitigating brightness disparities by sinking current from the LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiplexed LED display operates with sequential row activation, then power consumption is reduced and display refresh rate is improved, but brightness uniformity across rows deteriorates due to forward voltage variations
Solution Approach 1:
The pre-discharge circuit performs preliminary discharge of stored charge in column outputs before the next row of LEDs is activated. This preliminary action equalizes the starting voltage conditions for each row, ensuring that brightness uniformity is maintained across all rows during sequential multiplexed operation.
Solution Approach 2:
The pre-discharge circuit applies a counteracting discharge current to neutralize the accumulated forward voltage differences between rows before they can cause brightness non-uniformity. This preliminary anti-action prevents the brightness inconsistency from manifesting in the final display output.
2Illumination intensity
If pre-discharge circuit is added to equalize row brightness, then brightness uniformity is improved, but device complexity increases due to additional discharge circuits
Solution Approach 1:
The pre-discharge circuit shares the same column output lines and control infrastructure with the normal display operation. The discharge transistors are integrated into the existing driver chip architecture, allowing the circuit to perform both normal LED driving and pre-discharge functions using overlapping hardware resources.
Solution Approach 2:
The pre-discharge functionality is merged with the existing column driver circuits. The discharge transistors are combined with the column output drivers in a single integrated circuit, and the pre-discharge operation is combined with the normal multiplexed scanning sequence, thereby reducing overall system complexity.
3Reliability
If pre-discharge phase is implemented before each row activation, then forward voltage differences are reduced, but operation timing complexity increases
Solution Approach 1:
The pre-discharge operation is implemented as a periodic action that occurs at regular intervals corresponding to each row activation cycle. The discharge transistors are turned on for a fixed duration immediately before each row is scanned, creating a rhythmic discharge pattern that simplifies timing control compared to variable or adaptive discharge schemes.
Solution Approach 2:
The pre-discharge phase is performed as a preliminary action with a fixed, predetermined duration before each row activation. This standardized preliminary timing simplifies the control logic by establishing a constant time relationship between discharge and activation events, reducing the complexity of timing coordination.
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
The pre-discharge circuit effectively reduces the differences in forward voltages between adjacent rows, resulting in a more even and consistent display intensity across the LED display.
Implementation Method 1
discharge the stored charge before the output driver circuit activates, reducing parasitic capacitance voltages
Data Source
AI summary
A system includes an output driver circuit configured to operate a light emitting diode (LED) display having a plurality of columns of LED devices. The output driver circuit is configured to drive a given column output for the plurality of columns of LED devices in response to being activated based on data and an driver on signal supplied to the output driver circuit. A pre-discharge circuit includes a separate discharge circuit connected to each of the column outputs. The pre-discharge circuit is configured to discharge the given column output for a predetermined period of time before the output driver circuit is activated.