# High Precision Control System for Micro-LED Displays
## 1 Introduction  
Display technology permeates daily life, work, and study, and it is essential to modern society. The prevailing technologies in the display industry at the current stage are liquid crystal display (LCD), light-emitting diode (LED) display, organic light-emitting diode (OLED) display, laser display and electronic paper display. LED display includes ordinary LED display, mini-LED display and micro-LED displays. Micro-LED chip size is below 50 microns and densely integrated onto a glass substrate. And micro-LED displays has the advantage of higher brightness, higher luminous efficacy, a faster response time and better color reproducibility than other display technologies [1; 2; 3; 4]. These advantages enable it to have broader application value in display scenarios, such as television (TV), mobile phones, wearable devices and augmented reality (AR) [5; 6; 7; 8; 9]. Due to its ability to achieve seamless stitching, it will be extensively used in large-size display.  
A great deal of research has been carried out in recent years on micro-LED displays, including driving control, uniformity regulation and refresh rate improvement [10; 11; 12; 13; 14; 15]. [PERSON] et al. presented a digital method to realize 16 \(\times\) GGG \(\times\) 29 micro-LED displays with a 60 Hz refresh rate [13]. Based on a low-temperature polysilicon (LTPS) thin-film transistor (TFT), Samsung used mixed modulation for the first time to directly convert voltage into luminescence time and control different grey-scales [16]. However, the development of micro-LED displays faces some bottlenecks. These include the lack of a dedicated driver IC for micro-LED displays, uneven micro-LED displays due to non-uniform TFT and LED differences and an obvious flicker phenomenon in low grey-scale due to the traditional scanning mode. The traditional scanning mode can achieve high refresh rates in high grey-scale but low refresh rates in low grey-scale. Micro-LED driving can be divided into activedriving and passive driving. The passive driving method is simple and easy to implement, but it is not capable of supporting high-resolution displays. In contrast, active driving technology based on a thin-film transistor (TFT) is used to drive Micro-LEDs. However, micro-LED is a current-driven light-emitting device. The direct current modulation method can lead to color casting problems because of the threshold voltage drift and carrier mobility difference during the TFT preparation. And the brightness fluctuation of micro-LED is caused by differences in the brightness between the micro-LED and the IR drop of TFT. A refresh rate that is too low will produce an obvious flicking sensation, and there will be scanning patterns when the image is captured by photographic equipment.  
In this study, we propose a FPGA-based control system that produces pulse width modulation (PWM) data voltages and control signals to precisely regulate the brightness of 24 \(\times\) 46 glass-based micro-LED displays, achieving 10-bit grey-scale. The high grey-scale refresh rate is 2100 Hz, and the low grey-scale refresh rate is 300 Hz. Additionally, the panel's uniformity can be enhanced through brightness correction. The paper proposes a digital-analogue hybrid method that combines the traditional direct current modulation method with PWM driving to achieve constant current drive control.