LED Backlight Voltage Calibration for HDR Display Uniformity
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Solution Overview
Problem
Current LED arrays in display devices, particularly in HDR displays, face challenges in maintaining consistent luminance and wide range of brightness intensities due to restrictive calibration methods, which are costly and limit the modulation range, especially at low operating points.
Innovation Solution
The solution involves using voltage variance to implement luminance calibration, allowing independent control of voltage and current to each LED, enabling full range control of LED intensity across operating points through modulation techniques like PWM, PCM, or polyphase, thereby ensuring uniform brightness and compensating for aging LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional LED binning calibration method is used, then LED luminance consistency is improved, but manufacturing cost increases and modulation range is limited
Solution Approach 1:
The patent changes the calibration parameter from luminance-based binning to voltage-based calibration. By calibrating each LED's forward voltage to a target value and using this calibrated voltage as the reference for PWM modulation, the system achieves luminance consistency without expensive binning. The calibrated voltage serves as a unique identifier and control reference for each LED, enabling cost-effective precision control.
Solution Approach 2:
The patent performs voltage calibration as a preliminary action during LED initialization or setup phase. Each LED's forward voltage is measured and stored in a lookup table before normal operation. This preliminary calibration data is then used during runtime to adjust PWM duty cycles, eliminating the need for continuous expensive luminance monitoring and enabling efficient luminance control throughout the LED's operational life.
2Manufacturing precision
If traditional calibration methods are used, then LED luminance consistency is improved, but modulation range especially at low operating points is reduced
Solution Approach 1:
The patent implements dynamic voltage adjustment based on temperature compensation. The calibrated forward voltage is not fixed but is dynamically adjusted using a temperature compensation formula that accounts for thermal effects on LED characteristics. This allows the system to maintain accurate luminance control across varying operating conditions while preserving the full modulation range, including low operating points that were previously unreachable.
Solution Approach 2:
The patent adds a voltage calibration dimension to the traditional PWM control approach. Instead of relying solely on PWM duty cycle adjustment, the system uses calibrated forward voltage as an additional control dimension. This creates a two-dimensional control space (voltage + PWM) that expands the effective modulation range and enables precise control at low operating points that would be difficult to achieve with PWM alone.
3Adaptability or versatility
If voltage variance calibration is applied, then full range PWM control is preserved, but system complexity increases
Solution Approach 1:
The patent implements self-service calibration where each LED's forward voltage is automatically measured, stored, and used for control without requiring external manual calibration equipment or complex calibration procedures. The system autonomously performs the calibration by applying test currents, measuring voltage drops, and storing the results in onboard memory. This self-calibrating approach reduces operational complexity while maintaining full PWM control range.
Solution Approach 2:
The patent replaces physical luminance measurement and adjustment mechanisms with electrical voltage measurement and digital storage. Instead of using optical sensors and mechanical adjustment components, the system uses electrical voltage characterization and stores calibration data in digital lookup tables. This substitution of electrical/digital methods for mechanical/optical methods simplifies the overall system architecture while preserving full PWM control capabilities.
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 approach allows for precise control of LED brightness, maintaining consistent luminance across the array, extending the modulation range, and ensuring each LED can reach minimum brightness, even at low drive values, thus enhancing the overall performance of HDR displays by preserving the full range of PWM control.
Implementation Method 1
The light source comprises, for example, an LED and the calibrated brightness control signal comprises, for example, a forward voltage of the LED
Implementation Method 2
The modulation technique is preferably PWM, but may be any of PWM, PCM, polyphase, others etc.
Implementation Method 3
uses voltage variance to implement luminance calibration to define one operating point, thereby preserving full range control of the LED intensity at all other operating points
Data Source
AI summary
Luminosity of individual LED light sources is measured and a forward voltage control of each LED is set so that each LED has a pre-determined (e.g., uniform) luminosity at a same modulation level. The LEDs are then driven via a modulation technique such as PWM, PCM, polyphase, etc. according to lighting requirements. The LEDs are, for example, a backlight of a dual modulation HDR LCD display system, and the lighting requirements are local dimming signals for the display.