Ramp Driver Circuit for Precise Micro LED Brightness Control
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Solution Overview
Problem
Micro LEDs face challenges in accurately controlling brightness due to shifts in current density, making it difficult to achieve intended brightness levels using pulse width modulation (PWM) pixel driving schemes.
Innovation Solution
A ramp driver is introduced, comprising a ramp generator and delayer, which generates and sequentially outputs a reference ramp signal using a resistor string to divide and output voltages, and includes stages with flip-flops and delay blocks to control the ramp signal, compensating for errors and adjusting brightness through a series of delay circuits and amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If pulse width modulation (PWM) pixel driving scheme is used to control micro LED brightness, then response speed and brightness control are improved, but brightness accuracy deteriorates due to current density shifts causing center wavelength changes
Solution Approach 1:
The patent changes the driving parameter from PWM (time-based duty cycle) to PAM (voltage-based amplitude modulation). By using a ramp driver to generate precise analog ramp signals that directly control the current amplitude rather than the time duration, the system achieves both fast response and accurate brightness control. The ramp signal voltage level directly determines the micro LED current and brightness, eliminating the wavelength shift issue inherent in PWM operation.
2Measurement precision
If ramp driver with resistor string is used to generate reference ramp signal, then brightness control precision is improved, but device complexity increases due to multiple stages and delay blocks
Solution Approach 1:
The patent segments the brightness control into multiple independent stages, each handling a specific portion of the ramp signal generation. The resistor string is divided into multiple segments (first through k-th resistors) that can be independently controlled by corresponding ramp switches. This segmentation allows the complex brightness control function to be distributed across simpler, modular stages, making the overall system more manageable while maintaining precision.
Solution Approach 2:
The patent introduces dynamic control elements including flip-flops and delay blocks that can be activated or deactivated based on the required brightness level. The ramp switches dynamically connect different portions of the resistor string to the output, and the delay blocks dynamically adjust the timing of ramp signal delivery to subpixels. This dynamic configuration allows the same hardware to adapt to different brightness requirements without increasing physical complexity.
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 ramp driver effectively controls brightness by generating accurate ramp signals, ensuring consistent and precise pixel illumination in micro LED displays, enhancing display performance.
Implementation Method 1
a ramp generator configured to generate a reference ramp signal, and including a resistor string including: a first end configured to receive a high ramp voltage; and a second end configured to receive a low ramp voltage
Data Source
AI summary
A ramp driver includes: a ramp generator to generate a reference ramp signal, and including a resistor string including: a first end to receive a high ramp voltage; and a second end to receive a low ramp voltage; and a ramp delayer to sequentially output the reference ramp signal. The ramp generator is to: divide the high ramp voltage into first through k-th voltages by utilizing the resistor string; and sequentially output the first through k-th voltages to generate the reference ramp signal, where k is a positive integer.