# High Precision Control System for Micro-LED Displays
## 2 Control System Architecture
We can assume that \(PWM+\Delta SWEEP=VREF\); thus, the \(SWEEP\) signal change relationship equation can be expressed as follows:  
\[\Delta SWEEP=VREF-PWM \tag{1}\]  
Different video data have different PWM signals that require different lighting times; the lighting time can be summarized as follows:  
\[T=\frac{|V_{REF}-V_{PWM}|}{V_{SWEEP}}\times T_{SWEEP}=\frac{\Delta V_{SWEEP}}{V _{SWEEP}}\times T_{SWEEP} \tag{2}\]  
Therefore, the grey level of the display is affected by the slope of the SWEEP amplitude drop. The counter and comparator are used to generate a 12-bit decreasing series, and then a 12-bit DAC is used to output a 12-bit precision ramp signal. Then, the ramp signal is stepped up to the drive voltage range through an amplifier circuit, thus achieving a high-precision SWEEP signal output, as shown in Figure 6.  
The 8-bit RGB video data read from RAM are fed into correction model and converted into 10-bit data via gamma transformation. Then, the 10-bit data are fed into 10-bit DAC and ADC to obtain the grey-scale voltage, also known as PWM  
Figure 4: The producing method of CLK1/CLK2/IN/NM/EM. Figure 5: The proposed PWM pixel circuit. The PWM data voltage can be expressed as follows:  
\[V_{PWM_{i}}\approx\left(32\cdot V\cdot R_{1}\cdot i\right/1024\cdot R_{2}\right) \cdot\left(V_{1}-V_{0}\right)\cdot\frac{R_{4}}{R_{5}}\cdot\frac{R_{7}}{R_{6}} \tag{3}\]  
where the V is the voltage at terminal voltage, R1 the is equivalent input load resistance and R2 is the external resistor of the DAC. Through digital-to-analogue conversion and two-stage amplification, we obtain the PWM data required to achieve real-time display. Differences in brightness between the micro-LED and the IR drop of TFT may cause inconsistent brightness of the micro-LED. To improve the quality of micro-LED displays, the panel must undergo correction, including gamma correction and brightness correction. Since luminance correction leads to a loss of grey-scale on the display, we implement front-end video correction. As Figure 8 shows, the RGB data are read out from the RAM for inverse gamma transformation, and the processed image data are corrected by the multiplication module. The processed image data undergo correction through a multiplication module, using CoeffR, CoefG and CoefB as correction parameters for the RGB corresponding to their respective image data. For every LED display pixel, there are three correction parameters. And the 10-bit image data of each primary color are multiplied by the corrected parameter values after quantization. The resulting calculations are output to the DAC, and then we can identify the data voltage. To guarantee synchronization between the data read from the dual-port RAM and the display timing of the panel, we executed memory management, as shown in Figure 9. The dual-port RAM is used to accomplish both the writing and reading of video data. The  
Figure 3:0 Brightness correction. Figure 3:1 The producing method of SWEEP. Figure 3:2 The producing method of PWM. writing address was regulated to choose the particular section of dual-port RAM for writing data, while the reading address was controlled to select which section of the dual-port RAM used to read data. When RAM1 is written, the data in RAM2 are read; when RAM2 is written, the data in RAM1 is read. The data written are serial, while the data read are parallel, meaning that the data readout frequency is decreased through down-sampling to match the display timing of the micro-LED. The pixel number of the micro-LED is 24 \(\times\) 46, and the input data are serial, meaning that the width of the input port is set at 30. Considering that both RAMs continuously read and write, the depth of the input port is set at 294. The output data are parallel, and only one row of data is read at a time, meaning that the width of the output port is 960.