LED Backlight Calibration Using Multiplexed Comparator
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Solution Overview
Problem
Existing LED backlighting systems for liquid crystal displays require complex calibration processes using specialized equipment and structures, which can be cumbersome and inefficient for ensuring uniform illumination across the display.
Innovation Solution
A system comprising current sources, control voltage sources, a comparator, and a multiplexer that simplifies the calibration of LED strings by adjusting control voltages to achieve equal current amplitudes across all LEDs, eliminating the need for special calibration structures and equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If specialized calibration systems with automatic test equipment and fuse arrays are used, then calibration precision is improved, but device complexity increases
Solution Approach 1:
The system uses self-calibration where the LED strings themselves serve as the calibration reference. Each LED string's forward voltage is measured and used to adjust its current, eliminating the need for external calibration equipment. The controller automatically reads forward voltages from all LED strings and adjusts current sources to equalize brightness without requiring specialized test equipment or fuse arrays.
Solution Approach 2:
The invention extracts and eliminates the complex external calibration equipment (automatic test equipment, fuse arrays, special interfaces) from the system. Instead, it uses only the essential components already present in the LED backlighting system (controller, current sources, and LED strings), removing the need for separate calibration systems while maintaining calibration precision.
2Illumination intensity
If multiple current sources are used to drive different LED strings, then illumination coverage is improved, but current uniformity deteriorates
Solution Approach 1:
The system implements feedback calibration by measuring the forward voltage of each LED string and using this information to adjust the current source settings. The controller reads the forward voltage from each LED string, compares it to reference values, and automatically adjusts the current sources to equalize the current through each string, ensuring uniform illumination across all LED strings despite manufacturing variations.
Solution Approach 2:
The invention changes the operating parameters of each current source based on measured forward voltage values. By adjusting the current source control voltages or current levels individually for each LED string based on their specific forward voltage characteristics, the system achieves uniform current distribution across all strings, compensating for manufacturing tolerances and ensuring consistent brightness.
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 enables efficient and uniform backlighting by ensuring equal illumination across the display, reducing the complexity of calibration processes and allowing for dynamic brightness adjustments through methods like analog dimming and pulse-width modulation.
Implementation Method 1
The comparator compares a voltage at an input port of the comparator to a reference voltage
Implementation Method 2
strings of light-emitting diodes (LEDs)
Implementation Method 3
light-emitting diodes (LEDs) can also be configured to provide other backlight colors
Data Source
AI summary
Lighting system embodiments are provided to energize and calibrate strings of light-emitting diodes. These embodiments are particularly useful for calibration of strings of light-emitting diodes that are arranged to provide backlighting of liquid crystal displays. The systems are structured around the use of a single comparator that is multiplexed to facilitate calibration of a plurality of current sources. The systems can be adapted for use in displays in which different techniques (e.g., “analog dimming” and “pulse-width modulation”) are used to vary the brightness of the display. The systems remove the need for special structures (e.g., fuse arrays, special test equipment, and interfaces).